Update draft release notes to 1.7.10
[git/git.git] / Documentation / user-manual.txt
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0eb4f7cd 1Git User's Manual (for version 1.5.3 or newer)
71f4b183 2______________________________________________
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4
5Git is a fast distributed revision control system.
6
02783075 7This manual is designed to be readable by someone with basic UNIX
79c96c57 8command-line skills, but no previous knowledge of git.
d19fbc3c 9
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10<<repositories-and-branches>> and <<exploring-git-history>> explain how
11to fetch and study a project using git--read these chapters to learn how
12to build and test a particular version of a software project, search for
13regressions, and so on.
ef89f701 14
2624d9a5 15People needing to do actual development will also want to read
aa971cb9 16<<Developing-With-git>> and <<sharing-development>>.
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17
18Further chapters cover more specialized topics.
19
d19fbc3c 20Comprehensive reference documentation is available through the man
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21pages, or linkgit:git-help[1] command. For example, for the command
22"git clone <repo>", you can either use:
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23
24------------------------------------------------
25$ man git-clone
26------------------------------------------------
27
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28or:
29
30------------------------------------------------
31$ git help clone
32------------------------------------------------
33
34With the latter, you can use the manual viewer of your choice; see
35linkgit:git-help[1] for more information.
36
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37See also <<git-quick-start>> for a brief overview of git commands,
38without any explanation.
b181d57f 39
99f171bb 40Finally, see <<todo>> for ways that you can help make this manual more
2624d9a5 41complete.
b181d57f 42
b181d57f 43
e34caace 44[[repositories-and-branches]]
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45Repositories and Branches
46=========================
47
e34caace 48[[how-to-get-a-git-repository]]
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49How to get a git repository
50---------------------------
51
52It will be useful to have a git repository to experiment with as you
53read this manual.
54
5162e697 55The best way to get one is by using the linkgit:git-clone[1] command to
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56download a copy of an existing repository. If you don't already have a
57project in mind, here are some interesting examples:
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58
59------------------------------------------------
60 # git itself (approx. 10MB download):
61$ git clone git://git.kernel.org/pub/scm/git/git.git
c7719fbe 62 # the Linux kernel (approx. 150MB download):
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63$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
64------------------------------------------------
65
66The initial clone may be time-consuming for a large project, but you
67will only need to clone once.
68
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69The clone command creates a new directory named after the project ("git"
70or "linux-2.6" in the examples above). After you cd into this
d19fbc3c 71directory, you will see that it contains a copy of the project files,
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72called the <<def_working_tree,working tree>>, together with a special
73top-level directory named ".git", which contains all the information
74about the history of the project.
d19fbc3c 75
e34caace 76[[how-to-check-out]]
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77How to check out a different version of a project
78-------------------------------------------------
79
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80Git is best thought of as a tool for storing the history of a collection
81of files. It stores the history as a compressed collection of
82interrelated snapshots of the project's contents. In git each such
83version is called a <<def_commit,commit>>.
d19fbc3c 84
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85Those snapshots aren't necessarily all arranged in a single line from
86oldest to newest; instead, work may simultaneously proceed along
57283291 87parallel lines of development, called <<def_branch,branches>>, which may
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88merge and diverge.
89
90A single git repository can track development on multiple branches. It
91does this by keeping a list of <<def_head,heads>> which reference the
5162e697 92latest commit on each branch; the linkgit:git-branch[1] command shows
81b6c950 93you the list of branch heads:
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94
95------------------------------------------------
96$ git branch
97* master
98------------------------------------------------
99
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100A freshly cloned repository contains a single branch head, by default
101named "master", with the working directory initialized to the state of
102the project referred to by that branch head.
d19fbc3c 103
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104Most projects also use <<def_tag,tags>>. Tags, like heads, are
105references into the project's history, and can be listed using the
5162e697 106linkgit:git-tag[1] command:
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107
108------------------------------------------------
109$ git tag -l
110v2.6.11
111v2.6.11-tree
112v2.6.12
113v2.6.12-rc2
114v2.6.12-rc3
115v2.6.12-rc4
116v2.6.12-rc5
117v2.6.12-rc6
118v2.6.13
119...
120------------------------------------------------
121
fe4b3e59 122Tags are expected to always point at the same version of a project,
81b6c950 123while heads are expected to advance as development progresses.
fe4b3e59 124
81b6c950 125Create a new branch head pointing to one of these versions and check it
5162e697 126out using linkgit:git-checkout[1]:
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127
128------------------------------------------------
129$ git checkout -b new v2.6.13
130------------------------------------------------
131
132The working directory then reflects the contents that the project had
5162e697 133when it was tagged v2.6.13, and linkgit:git-branch[1] shows two
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134branches, with an asterisk marking the currently checked-out branch:
135
136------------------------------------------------
137$ git branch
138 master
139* new
140------------------------------------------------
141
142If you decide that you'd rather see version 2.6.17, you can modify
143the current branch to point at v2.6.17 instead, with
144
145------------------------------------------------
146$ git reset --hard v2.6.17
147------------------------------------------------
148
81b6c950 149Note that if the current branch head was your only reference to a
d19fbc3c 150particular point in history, then resetting that branch may leave you
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151with no way to find the history it used to point to; so use this command
152carefully.
d19fbc3c 153
e34caace 154[[understanding-commits]]
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155Understanding History: Commits
156------------------------------
157
158Every change in the history of a project is represented by a commit.
5162e697 159The linkgit:git-show[1] command shows the most recent commit on the
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160current branch:
161
162------------------------------------------------
163$ git show
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164commit 17cf781661e6d38f737f15f53ab552f1e95960d7
165Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)>
166Date: Tue Apr 19 14:11:06 2005 -0700
167
168 Remove duplicate getenv(DB_ENVIRONMENT) call
169
170 Noted by Tony Luck.
171
172diff --git a/init-db.c b/init-db.c
173index 65898fa..b002dc6 100644
174--- a/init-db.c
175+++ b/init-db.c
176@@ -7,7 +7,7 @@
d19fbc3c 177
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178 int main(int argc, char **argv)
179 {
180- char *sha1_dir = getenv(DB_ENVIRONMENT), *path;
181+ char *sha1_dir, *path;
182 int len, i;
183
184 if (mkdir(".git", 0755) < 0) {
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185------------------------------------------------
186
187As you can see, a commit shows who made the latest change, what they
188did, and why.
189
35121930 190Every commit has a 40-hexdigit id, sometimes called the "object name" or the
a6e5ef7d 191"SHA-1 id", shown on the first line of the "git show" output. You can usually
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192refer to a commit by a shorter name, such as a tag or a branch name, but this
193longer name can also be useful. Most importantly, it is a globally unique
194name for this commit: so if you tell somebody else the object name (for
195example in email), then you are guaranteed that name will refer to the same
196commit in their repository that it does in yours (assuming their repository
197has that commit at all). Since the object name is computed as a hash over the
198contents of the commit, you are guaranteed that the commit can never change
199without its name also changing.
200
036f8199 201In fact, in <<git-concepts>> we shall see that everything stored in git
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202history, including file data and directory contents, is stored in an object
203with a name that is a hash of its contents.
d19fbc3c 204
e34caace 205[[understanding-reachability]]
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206Understanding history: commits, parents, and reachability
207~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
208
209Every commit (except the very first commit in a project) also has a
210parent commit which shows what happened before this commit.
211Following the chain of parents will eventually take you back to the
212beginning of the project.
213
214However, the commits do not form a simple list; git allows lines of
215development to diverge and then reconverge, and the point where two
216lines of development reconverge is called a "merge". The commit
217representing a merge can therefore have more than one parent, with
218each parent representing the most recent commit on one of the lines
219of development leading to that point.
220
5162e697 221The best way to see how this works is using the linkgit:gitk[1]
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222command; running gitk now on a git repository and looking for merge
223commits will help understand how the git organizes history.
224
225In the following, we say that commit X is "reachable" from commit Y
226if commit X is an ancestor of commit Y. Equivalently, you could say
02783075 227that Y is a descendant of X, or that there is a chain of parents
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228leading from commit Y to commit X.
229
e34caace 230[[history-diagrams]]
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231Understanding history: History diagrams
232~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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233
234We will sometimes represent git history using diagrams like the one
235below. Commits are shown as "o", and the links between them with
236lines drawn with - / and \. Time goes left to right:
237
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238
239................................................
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240 o--o--o <-- Branch A
241 /
242 o--o--o <-- master
243 \
244 o--o--o <-- Branch B
1dc71a91 245................................................
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246
247If we need to talk about a particular commit, the character "o" may
248be replaced with another letter or number.
249
e34caace 250[[what-is-a-branch]]
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251Understanding history: What is a branch?
252~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
253
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254When we need to be precise, we will use the word "branch" to mean a line
255of development, and "branch head" (or just "head") to mean a reference
256to the most recent commit on a branch. In the example above, the branch
257head named "A" is a pointer to one particular commit, but we refer to
258the line of three commits leading up to that point as all being part of
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259"branch A".
260
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261However, when no confusion will result, we often just use the term
262"branch" both for branches and for branch heads.
d19fbc3c 263
e34caace 264[[manipulating-branches]]
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265Manipulating branches
266---------------------
267
268Creating, deleting, and modifying branches is quick and easy; here's
269a summary of the commands:
270
271git branch::
272 list all branches
273git branch <branch>::
274 create a new branch named <branch>, referencing the same
275 point in history as the current branch
276git branch <branch> <start-point>::
277 create a new branch named <branch>, referencing
278 <start-point>, which may be specified any way you like,
279 including using a branch name or a tag name
280git branch -d <branch>::
281 delete the branch <branch>; if the branch you are deleting
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282 points to a commit which is not reachable from the current
283 branch, this command will fail with a warning.
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284git branch -D <branch>::
285 even if the branch points to a commit not reachable
286 from the current branch, you may know that that commit
287 is still reachable from some other branch or tag. In that
288 case it is safe to use this command to force git to delete
289 the branch.
290git checkout <branch>::
291 make the current branch <branch>, updating the working
292 directory to reflect the version referenced by <branch>
293git checkout -b <new> <start-point>::
294 create a new branch <new> referencing <start-point>, and
295 check it out.
296
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297The special symbol "HEAD" can always be used to refer to the current
298branch. In fact, git uses a file named "HEAD" in the .git directory to
299remember which branch is current:
300
301------------------------------------------------
302$ cat .git/HEAD
303ref: refs/heads/master
304------------------------------------------------
305
25d9f3fa 306[[detached-head]]
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307Examining an old version without creating a new branch
308------------------------------------------------------
309
6127c086 310The `git checkout` command normally expects a branch head, but will also
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311accept an arbitrary commit; for example, you can check out the commit
312referenced by a tag:
313
314------------------------------------------------
315$ git checkout v2.6.17
316Note: moving to "v2.6.17" which isn't a local branch
317If you want to create a new branch from this checkout, you may do so
318(now or later) by using -b with the checkout command again. Example:
319 git checkout -b <new_branch_name>
320HEAD is now at 427abfa... Linux v2.6.17
321------------------------------------------------
322
a6e5ef7d 323The HEAD then refers to the SHA-1 of the commit instead of to a branch,
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324and git branch shows that you are no longer on a branch:
325
326------------------------------------------------
327$ cat .git/HEAD
328427abfa28afedffadfca9dd8b067eb6d36bac53f
953f3d6f 329$ git branch
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330* (no branch)
331 master
332------------------------------------------------
333
334In this case we say that the HEAD is "detached".
335
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336This is an easy way to check out a particular version without having to
337make up a name for the new branch. You can still create a new branch
338(or tag) for this version later if you decide to.
d19fbc3c 339
e34caace 340[[examining-remote-branches]]
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341Examining branches from a remote repository
342-------------------------------------------
343
344The "master" branch that was created at the time you cloned is a copy
345of the HEAD in the repository that you cloned from. That repository
346may also have had other branches, though, and your local repository
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347keeps branches which track each of those remote branches, called
348remote-tracking branches, which you
5162e697 349can view using the "-r" option to linkgit:git-branch[1]:
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350
351------------------------------------------------
352$ git branch -r
353 origin/HEAD
354 origin/html
355 origin/maint
356 origin/man
357 origin/master
358 origin/next
359 origin/pu
360 origin/todo
361------------------------------------------------
362
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363In this example, "origin" is called a remote repository, or "remote"
364for short. The branches of this repository are called "remote
365branches" from our point of view. The remote-tracking branches listed
366above were created based on the remote branches at clone time and will
367be updated by "git fetch" (hence "git pull") and "git push". See
368<<Updating-a-repository-With-git-fetch>> for details.
369
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370You might want to build on one of these remote-tracking branches
371on a branch of your own, just as you would for a tag:
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372
373------------------------------------------------
374$ git checkout -b my-todo-copy origin/todo
375------------------------------------------------
376
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377You can also check out "origin/todo" directly to examine it or
378write a one-off patch. See <<detached-head,detached head>>.
379
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380Note that the name "origin" is just the name that git uses by default
381to refer to the repository that you cloned from.
382
383[[how-git-stores-references]]
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384Naming branches, tags, and other references
385-------------------------------------------
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386
387Branches, remote-tracking branches, and tags are all references to
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388commits. All references are named with a slash-separated path name
389starting with "refs"; the names we've been using so far are actually
390shorthand:
d19fbc3c 391
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392 - The branch "test" is short for "refs/heads/test".
393 - The tag "v2.6.18" is short for "refs/tags/v2.6.18".
394 - "origin/master" is short for "refs/remotes/origin/master".
d19fbc3c 395
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396The full name is occasionally useful if, for example, there ever
397exists a tag and a branch with the same name.
d19fbc3c 398
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399(Newly created refs are actually stored in the .git/refs directory,
400under the path given by their name. However, for efficiency reasons
401they may also be packed together in a single file; see
5162e697 402linkgit:git-pack-refs[1]).
fc74ecc1 403
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404As another useful shortcut, the "HEAD" of a repository can be referred
405to just using the name of that repository. So, for example, "origin"
406is usually a shortcut for the HEAD branch in the repository "origin".
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407
408For the complete list of paths which git checks for references, and
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409the order it uses to decide which to choose when there are multiple
410references with the same shorthand name, see the "SPECIFYING
9d83e382 411REVISIONS" section of linkgit:gitrevisions[7].
d19fbc3c 412
aa971cb9 413[[Updating-a-repository-With-git-fetch]]
6127c086 414Updating a repository with git fetch
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415------------------------------------
416
417Eventually the developer cloned from will do additional work in her
418repository, creating new commits and advancing the branches to point
419at the new commits.
420
421The command "git fetch", with no arguments, will update all of the
422remote-tracking branches to the latest version found in her
423repository. It will not touch any of your own branches--not even the
424"master" branch that was created for you on clone.
425
e34caace 426[[fetching-branches]]
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427Fetching branches from other repositories
428-----------------------------------------
429
430You can also track branches from repositories other than the one you
5162e697 431cloned from, using linkgit:git-remote[1]:
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432
433-------------------------------------------------
434$ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git
04483524 435$ git fetch linux-nfs
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436* refs/remotes/linux-nfs/master: storing branch 'master' ...
437 commit: bf81b46
438-------------------------------------------------
439
440New remote-tracking branches will be stored under the shorthand name
6127c086 441that you gave "git remote add", in this case linux-nfs:
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442
443-------------------------------------------------
444$ git branch -r
445linux-nfs/master
446origin/master
447-------------------------------------------------
448
8b3f3f84 449If you run "git fetch <remote>" later, the remote-tracking branches for the
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450named <remote> will be updated.
451
452If you examine the file .git/config, you will see that git has added
453a new stanza:
454
455-------------------------------------------------
456$ cat .git/config
457...
458[remote "linux-nfs"]
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459 url = git://linux-nfs.org/pub/nfs-2.6.git
460 fetch = +refs/heads/*:refs/remotes/linux-nfs/*
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461...
462-------------------------------------------------
463
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464This is what causes git to track the remote's branches; you may modify
465or delete these configuration options by editing .git/config with a
466text editor. (See the "CONFIGURATION FILE" section of
5162e697 467linkgit:git-config[1] for details.)
d5cd5de4 468
e34caace 469[[exploring-git-history]]
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470Exploring git history
471=====================
472
473Git is best thought of as a tool for storing the history of a
474collection of files. It does this by storing compressed snapshots of
1130845b 475the contents of a file hierarchy, together with "commits" which show
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476the relationships between these snapshots.
477
478Git provides extremely flexible and fast tools for exploring the
479history of a project.
480
aacd404e 481We start with one specialized tool that is useful for finding the
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482commit that introduced a bug into a project.
483
e34caace 484[[using-bisect]]
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485How to use bisect to find a regression
486--------------------------------------
487
488Suppose version 2.6.18 of your project worked, but the version at
489"master" crashes. Sometimes the best way to find the cause of such a
490regression is to perform a brute-force search through the project's
491history to find the particular commit that caused the problem. The
5162e697 492linkgit:git-bisect[1] command can help you do this:
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493
494-------------------------------------------------
495$ git bisect start
496$ git bisect good v2.6.18
497$ git bisect bad master
498Bisecting: 3537 revisions left to test after this
499[65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]
500-------------------------------------------------
501
502If you run "git branch" at this point, you'll see that git has
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503temporarily moved you in "(no branch)". HEAD is now detached from any
504branch and points directly to a commit (with commit id 65934...) that
505is reachable from "master" but not from v2.6.18. Compile and test it,
506and see whether it crashes. Assume it does crash. Then:
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507
508-------------------------------------------------
509$ git bisect bad
510Bisecting: 1769 revisions left to test after this
511[7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings
512-------------------------------------------------
513
514checks out an older version. Continue like this, telling git at each
515stage whether the version it gives you is good or bad, and notice
516that the number of revisions left to test is cut approximately in
517half each time.
518
519After about 13 tests (in this case), it will output the commit id of
520the guilty commit. You can then examine the commit with
5162e697 521linkgit:git-show[1], find out who wrote it, and mail them your bug
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522report with the commit id. Finally, run
523
524-------------------------------------------------
525$ git bisect reset
526-------------------------------------------------
527
0e25790f 528to return you to the branch you were on before.
d19fbc3c 529
6127c086 530Note that the version which `git bisect` checks out for you at each
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531point is just a suggestion, and you're free to try a different
532version if you think it would be a good idea. For example,
533occasionally you may land on a commit that broke something unrelated;
534run
535
536-------------------------------------------------
04483524 537$ git bisect visualize
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538-------------------------------------------------
539
540which will run gitk and label the commit it chose with a marker that
843c81dc 541says "bisect". Choose a safe-looking commit nearby, note its commit
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542id, and check it out with:
543
544-------------------------------------------------
545$ git reset --hard fb47ddb2db...
546-------------------------------------------------
547
548then test, run "bisect good" or "bisect bad" as appropriate, and
549continue.
550
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551Instead of "git bisect visualize" and then "git reset --hard
552fb47ddb2db...", you might just want to tell git that you want to skip
553the current commit:
554
555-------------------------------------------------
556$ git bisect skip
557-------------------------------------------------
558
559In this case, though, git may not eventually be able to tell the first
a0178ae2 560bad one between some first skipped commits and a later bad commit.
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561
562There are also ways to automate the bisecting process if you have a
563test script that can tell a good from a bad commit. See
564linkgit:git-bisect[1] for more information about this and other "git
565bisect" features.
566
e34caace 567[[naming-commits]]
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568Naming commits
569--------------
570
571We have seen several ways of naming commits already:
572
d55ae921 573 - 40-hexdigit object name
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574 - branch name: refers to the commit at the head of the given
575 branch
576 - tag name: refers to the commit pointed to by the given tag
577 (we've seen branches and tags are special cases of
578 <<how-git-stores-references,references>>).
579 - HEAD: refers to the head of the current branch
580
eb6ae7f4 581There are many more; see the "SPECIFYING REVISIONS" section of the
9d83e382 582linkgit:gitrevisions[7] man page for the complete list of ways to
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583name revisions. Some examples:
584
585-------------------------------------------------
d55ae921 586$ git show fb47ddb2 # the first few characters of the object name
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587 # are usually enough to specify it uniquely
588$ git show HEAD^ # the parent of the HEAD commit
589$ git show HEAD^^ # the grandparent
590$ git show HEAD~4 # the great-great-grandparent
591-------------------------------------------------
592
593Recall that merge commits may have more than one parent; by default,
594^ and ~ follow the first parent listed in the commit, but you can
595also choose:
596
597-------------------------------------------------
598$ git show HEAD^1 # show the first parent of HEAD
599$ git show HEAD^2 # show the second parent of HEAD
600-------------------------------------------------
601
602In addition to HEAD, there are several other special names for
603commits:
604
605Merges (to be discussed later), as well as operations such as
6127c086 606`git reset`, which change the currently checked-out commit, generally
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607set ORIG_HEAD to the value HEAD had before the current operation.
608
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FC
609The `git fetch` operation always stores the head of the last fetched
610branch in FETCH_HEAD. For example, if you run `git fetch` without
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611specifying a local branch as the target of the operation
612
613-------------------------------------------------
614$ git fetch git://example.com/proj.git theirbranch
615-------------------------------------------------
616
617the fetched commits will still be available from FETCH_HEAD.
618
619When we discuss merges we'll also see the special name MERGE_HEAD,
620which refers to the other branch that we're merging in to the current
621branch.
622
5162e697 623The linkgit:git-rev-parse[1] command is a low-level command that is
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624occasionally useful for translating some name for a commit to the object
625name for that commit:
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626
627-------------------------------------------------
628$ git rev-parse origin
629e05db0fd4f31dde7005f075a84f96b360d05984b
630-------------------------------------------------
631
e34caace 632[[creating-tags]]
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633Creating tags
634-------------
635
636We can also create a tag to refer to a particular commit; after
637running
638
639-------------------------------------------------
04483524 640$ git tag stable-1 1b2e1d63ff
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641-------------------------------------------------
642
643You can use stable-1 to refer to the commit 1b2e1d63ff.
644
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645This creates a "lightweight" tag. If you would also like to include a
646comment with the tag, and possibly sign it cryptographically, then you
5162e697 647should create a tag object instead; see the linkgit:git-tag[1] man page
c64415e2 648for details.
d19fbc3c 649
e34caace 650[[browsing-revisions]]
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651Browsing revisions
652------------------
653
5162e697 654The linkgit:git-log[1] command can show lists of commits. On its
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655own, it shows all commits reachable from the parent commit; but you
656can also make more specific requests:
657
658-------------------------------------------------
659$ git log v2.5.. # commits since (not reachable from) v2.5
660$ git log test..master # commits reachable from master but not test
661$ git log master..test # ...reachable from test but not master
662$ git log master...test # ...reachable from either test or master,
663 # but not both
664$ git log --since="2 weeks ago" # commits from the last 2 weeks
665$ git log Makefile # commits which modify Makefile
666$ git log fs/ # ... which modify any file under fs/
667$ git log -S'foo()' # commits which add or remove any file data
668 # matching the string 'foo()'
669-------------------------------------------------
670
671And of course you can combine all of these; the following finds
672commits since v2.5 which touch the Makefile or any file under fs:
673
674-------------------------------------------------
675$ git log v2.5.. Makefile fs/
676-------------------------------------------------
677
678You can also ask git log to show patches:
679
680-------------------------------------------------
681$ git log -p
682-------------------------------------------------
683
5162e697 684See the "--pretty" option in the linkgit:git-log[1] man page for more
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685display options.
686
687Note that git log starts with the most recent commit and works
688backwards through the parents; however, since git history can contain
3dff5379 689multiple independent lines of development, the particular order that
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690commits are listed in may be somewhat arbitrary.
691
e34caace 692[[generating-diffs]]
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693Generating diffs
694----------------
695
696You can generate diffs between any two versions using
5162e697 697linkgit:git-diff[1]:
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698
699-------------------------------------------------
700$ git diff master..test
701-------------------------------------------------
702
5b98d9bc
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703That will produce the diff between the tips of the two branches. If
704you'd prefer to find the diff from their common ancestor to test, you
705can use three dots instead of two:
706
707-------------------------------------------------
708$ git diff master...test
709-------------------------------------------------
710
711Sometimes what you want instead is a set of patches; for this you can
5162e697 712use linkgit:git-format-patch[1]:
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713
714-------------------------------------------------
715$ git format-patch master..test
716-------------------------------------------------
717
718will generate a file with a patch for each commit reachable from test
5b98d9bc 719but not from master.
d19fbc3c 720
e34caace 721[[viewing-old-file-versions]]
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722Viewing old file versions
723-------------------------
724
725You can always view an old version of a file by just checking out the
726correct revision first. But sometimes it is more convenient to be
727able to view an old version of a single file without checking
728anything out; this command does that:
729
730-------------------------------------------------
731$ git show v2.5:fs/locks.c
732-------------------------------------------------
733
734Before the colon may be anything that names a commit, and after it
735may be any path to a file tracked by git.
736
e34caace 737[[history-examples]]
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738Examples
739--------
740
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741[[counting-commits-on-a-branch]]
742Counting the number of commits on a branch
743~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
744
745Suppose you want to know how many commits you've made on "mybranch"
746since it diverged from "origin":
747
748-------------------------------------------------
749$ git log --pretty=oneline origin..mybranch | wc -l
750-------------------------------------------------
751
752Alternatively, you may often see this sort of thing done with the
a6e5ef7d 753lower-level command linkgit:git-rev-list[1], which just lists the SHA-1's
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754of all the given commits:
755
756-------------------------------------------------
757$ git rev-list origin..mybranch | wc -l
758-------------------------------------------------
759
e34caace 760[[checking-for-equal-branches]]
aec053bb 761Check whether two branches point at the same history
2f99710c 762~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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763
764Suppose you want to check whether two branches point at the same point
765in history.
766
767-------------------------------------------------
768$ git diff origin..master
769-------------------------------------------------
770
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771will tell you whether the contents of the project are the same at the
772two branches; in theory, however, it's possible that the same project
773contents could have been arrived at by two different historical
d55ae921 774routes. You could compare the object names:
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775
776-------------------------------------------------
777$ git rev-list origin
778e05db0fd4f31dde7005f075a84f96b360d05984b
779$ git rev-list master
780e05db0fd4f31dde7005f075a84f96b360d05984b
781-------------------------------------------------
782
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783Or you could recall that the ... operator selects all commits
784contained reachable from either one reference or the other but not
785both: so
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786
787-------------------------------------------------
788$ git log origin...master
789-------------------------------------------------
790
791will return no commits when the two branches are equal.
792
e34caace 793[[finding-tagged-descendants]]
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794Find first tagged version including a given fix
795~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
aec053bb 796
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797Suppose you know that the commit e05db0fd fixed a certain problem.
798You'd like to find the earliest tagged release that contains that
799fix.
800
801Of course, there may be more than one answer--if the history branched
802after commit e05db0fd, then there could be multiple "earliest" tagged
803releases.
804
805You could just visually inspect the commits since e05db0fd:
806
807-------------------------------------------------
808$ gitk e05db0fd..
809-------------------------------------------------
810
5162e697 811Or you can use linkgit:git-name-rev[1], which will give the commit a
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812name based on any tag it finds pointing to one of the commit's
813descendants:
814
815-------------------------------------------------
04483524 816$ git name-rev --tags e05db0fd
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817e05db0fd tags/v1.5.0-rc1^0~23
818-------------------------------------------------
819
5162e697 820The linkgit:git-describe[1] command does the opposite, naming the
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821revision using a tag on which the given commit is based:
822
823-------------------------------------------------
824$ git describe e05db0fd
04483524 825v1.5.0-rc0-260-ge05db0f
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826-------------------------------------------------
827
828but that may sometimes help you guess which tags might come after the
829given commit.
830
831If you just want to verify whether a given tagged version contains a
5162e697 832given commit, you could use linkgit:git-merge-base[1]:
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833
834-------------------------------------------------
835$ git merge-base e05db0fd v1.5.0-rc1
836e05db0fd4f31dde7005f075a84f96b360d05984b
837-------------------------------------------------
838
839The merge-base command finds a common ancestor of the given commits,
840and always returns one or the other in the case where one is a
841descendant of the other; so the above output shows that e05db0fd
842actually is an ancestor of v1.5.0-rc1.
843
844Alternatively, note that
845
846-------------------------------------------------
4a7979ca 847$ git log v1.5.0-rc1..e05db0fd
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848-------------------------------------------------
849
4a7979ca 850will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
b181d57f 851because it outputs only commits that are not reachable from v1.5.0-rc1.
aec053bb 852
5162e697 853As yet another alternative, the linkgit:git-show-branch[1] command lists
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854the commits reachable from its arguments with a display on the left-hand
855side that indicates which arguments that commit is reachable from. So,
856you can run something like
857
858-------------------------------------------------
859$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2
860! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
861available
862 ! [v1.5.0-rc0] GIT v1.5.0 preview
863 ! [v1.5.0-rc1] GIT v1.5.0-rc1
864 ! [v1.5.0-rc2] GIT v1.5.0-rc2
865...
866-------------------------------------------------
867
868then search for a line that looks like
869
870-------------------------------------------------
871+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
872available
873-------------------------------------------------
874
875Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and
876from v1.5.0-rc2, but not from v1.5.0-rc0.
877
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878[[showing-commits-unique-to-a-branch]]
879Showing commits unique to a given branch
880~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4a7979ca 881
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882Suppose you would like to see all the commits reachable from the branch
883head named "master" but not from any other head in your repository.
d19fbc3c 884
629d9f78 885We can list all the heads in this repository with
5162e697 886linkgit:git-show-ref[1]:
d19fbc3c 887
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888-------------------------------------------------
889$ git show-ref --heads
890bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial
891db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint
892a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master
89324dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2
8941e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes
895-------------------------------------------------
d19fbc3c 896
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897We can get just the branch-head names, and remove "master", with
898the help of the standard utilities cut and grep:
899
900-------------------------------------------------
901$ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master'
902refs/heads/core-tutorial
903refs/heads/maint
904refs/heads/tutorial-2
905refs/heads/tutorial-fixes
906-------------------------------------------------
907
908And then we can ask to see all the commits reachable from master
909but not from these other heads:
910
911-------------------------------------------------
912$ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |
913 grep -v '^refs/heads/master' )
914-------------------------------------------------
915
916Obviously, endless variations are possible; for example, to see all
917commits reachable from some head but not from any tag in the repository:
918
919-------------------------------------------------
c78974f7 920$ gitk $( git show-ref --heads ) --not $( git show-ref --tags )
629d9f78
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921-------------------------------------------------
922
9d83e382 923(See linkgit:gitrevisions[7] for explanations of commit-selecting
629d9f78
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924syntax such as `--not`.)
925
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926[[making-a-release]]
927Creating a changelog and tarball for a software release
928~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
929
5162e697 930The linkgit:git-archive[1] command can create a tar or zip archive from
82c8bf28
BF
931any version of a project; for example:
932
933-------------------------------------------------
934$ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz
935-------------------------------------------------
936
937will use HEAD to produce a tar archive in which each filename is
ccd71866 938preceded by "project/".
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939
940If you're releasing a new version of a software project, you may want
941to simultaneously make a changelog to include in the release
942announcement.
943
944Linus Torvalds, for example, makes new kernel releases by tagging them,
945then running:
946
947-------------------------------------------------
948$ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7
949-------------------------------------------------
950
951where release-script is a shell script that looks like:
952
953-------------------------------------------------
954#!/bin/sh
955stable="$1"
956last="$2"
957new="$3"
958echo "# git tag v$new"
959echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"
960echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"
961echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"
962echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"
963echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"
964-------------------------------------------------
965
966and then he just cut-and-pastes the output commands after verifying that
967they look OK.
4a7979ca 968
e1ba4c32 969[[Finding-commits-With-given-Content]]
187b0d80 970Finding commits referencing a file with given content
d5821de2 971~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
187b0d80
BF
972
973Somebody hands you a copy of a file, and asks which commits modified a
974file such that it contained the given content either before or after the
975commit. You can find out with this:
976
977-------------------------------------------------
477ff5b7 978$ git log --raw --abbrev=40 --pretty=oneline |
187b0d80
BF
979 grep -B 1 `git hash-object filename`
980-------------------------------------------------
981
982Figuring out why this works is left as an exercise to the (advanced)
5162e697
DM
983student. The linkgit:git-log[1], linkgit:git-diff-tree[1], and
984linkgit:git-hash-object[1] man pages may prove helpful.
187b0d80 985
aa971cb9 986[[Developing-With-git]]
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987Developing with git
988===================
989
e34caace 990[[telling-git-your-name]]
d19fbc3c
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991Telling git your name
992---------------------
993
994Before creating any commits, you should introduce yourself to git. The
58c19d1f
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995easiest way to do so is to make sure the following lines appear in a
996file named .gitconfig in your home directory:
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997
998------------------------------------------------
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999[user]
1000 name = Your Name Comes Here
1001 email = you@yourdomain.example.com
d19fbc3c
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1002------------------------------------------------
1003
5162e697 1004(See the "CONFIGURATION FILE" section of linkgit:git-config[1] for
fc90c536
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1005details on the configuration file.)
1006
d19fbc3c 1007
e34caace 1008[[creating-a-new-repository]]
d19fbc3c
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1009Creating a new repository
1010-------------------------
1011
1012Creating a new repository from scratch is very easy:
1013
1014-------------------------------------------------
1015$ mkdir project
1016$ cd project
f1d2b477 1017$ git init
d19fbc3c
BF
1018-------------------------------------------------
1019
1020If you have some initial content (say, a tarball):
1021
1022-------------------------------------------------
0ddd93b2 1023$ tar xzvf project.tar.gz
d19fbc3c 1024$ cd project
f1d2b477 1025$ git init
d19fbc3c
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1026$ git add . # include everything below ./ in the first commit:
1027$ git commit
1028-------------------------------------------------
1029
1030[[how-to-make-a-commit]]
ae25c67a 1031How to make a commit
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1032--------------------
1033
1034Creating a new commit takes three steps:
1035
1036 1. Making some changes to the working directory using your
1037 favorite editor.
1038 2. Telling git about your changes.
1039 3. Creating the commit using the content you told git about
1040 in step 2.
1041
1042In practice, you can interleave and repeat steps 1 and 2 as many
1043times as you want: in order to keep track of what you want committed
1044at step 3, git maintains a snapshot of the tree's contents in a
1045special staging area called "the index."
1046
01997b4a
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1047At the beginning, the content of the index will be identical to
1048that of the HEAD. The command "git diff --cached", which shows
1049the difference between the HEAD and the index, should therefore
1050produce no output at that point.
eb6ae7f4 1051
d19fbc3c
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1052Modifying the index is easy:
1053
1054To update the index with the new contents of a modified file, use
1055
1056-------------------------------------------------
1057$ git add path/to/file
1058-------------------------------------------------
1059
1060To add the contents of a new file to the index, use
1061
1062-------------------------------------------------
1063$ git add path/to/file
1064-------------------------------------------------
1065
eb6ae7f4 1066To remove a file from the index and from the working tree,
d19fbc3c
BF
1067
1068-------------------------------------------------
1069$ git rm path/to/file
1070-------------------------------------------------
1071
1072After each step you can verify that
1073
1074-------------------------------------------------
1075$ git diff --cached
1076-------------------------------------------------
1077
1078always shows the difference between the HEAD and the index file--this
1079is what you'd commit if you created the commit now--and that
1080
1081-------------------------------------------------
1082$ git diff
1083-------------------------------------------------
1084
1085shows the difference between the working tree and the index file.
1086
6127c086 1087Note that "git add" always adds just the current contents of a file
d19fbc3c 1088to the index; further changes to the same file will be ignored unless
6127c086 1089you run `git add` on the file again.
d19fbc3c
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1090
1091When you're ready, just run
1092
1093-------------------------------------------------
1094$ git commit
1095-------------------------------------------------
1096
1097and git will prompt you for a commit message and then create the new
3dff5379 1098commit. Check to make sure it looks like what you expected with
d19fbc3c
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1099
1100-------------------------------------------------
1101$ git show
1102-------------------------------------------------
1103
1104As a special shortcut,
a6080a0a 1105
d19fbc3c
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1106-------------------------------------------------
1107$ git commit -a
1108-------------------------------------------------
1109
1110will update the index with any files that you've modified or removed
1111and create a commit, all in one step.
1112
1113A number of commands are useful for keeping track of what you're
1114about to commit:
1115
1116-------------------------------------------------
1117$ git diff --cached # difference between HEAD and the index; what
1130845b 1118 # would be committed if you ran "commit" now.
d19fbc3c
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1119$ git diff # difference between the index file and your
1120 # working directory; changes that would not
1121 # be included if you ran "commit" now.
c64415e2
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1122$ git diff HEAD # difference between HEAD and working tree; what
1123 # would be committed if you ran "commit -a" now.
d19fbc3c
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1124$ git status # a brief per-file summary of the above.
1125-------------------------------------------------
1126
5162e697 1127You can also use linkgit:git-gui[1] to create commits, view changes in
407c0c87
BF
1128the index and the working tree files, and individually select diff hunks
1129for inclusion in the index (by right-clicking on the diff hunk and
1130choosing "Stage Hunk For Commit").
1131
e34caace 1132[[creating-good-commit-messages]]
ae25c67a 1133Creating good commit messages
d19fbc3c
BF
1134-----------------------------
1135
1136Though not required, it's a good idea to begin the commit message
1137with a single short (less than 50 character) line summarizing the
1138change, followed by a blank line and then a more thorough
1139description. Tools that turn commits into email, for example, use
1140the first line on the Subject line and the rest of the commit in the
1141body.
1142
2dc53617
JH
1143[[ignoring-files]]
1144Ignoring files
1145--------------
1146
1147A project will often generate files that you do 'not' want to track with git.
1148This typically includes files generated by a build process or temporary
1149backup files made by your editor. Of course, 'not' tracking files with git
6127c086 1150is just a matter of 'not' calling `git add` on them. But it quickly becomes
2dc53617 1151annoying to have these untracked files lying around; e.g. they make
dcb11263
CJ
1152`git add .` practically useless, and they keep showing up in the output of
1153`git status`.
2dc53617 1154
464a8a7a
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1155You can tell git to ignore certain files by creating a file called .gitignore
1156in the top level of your working directory, with contents such as:
2dc53617
JH
1157
1158-------------------------------------------------
1159# Lines starting with '#' are considered comments.
464a8a7a 1160# Ignore any file named foo.txt.
2dc53617
JH
1161foo.txt
1162# Ignore (generated) html files,
1163*.html
1164# except foo.html which is maintained by hand.
1165!foo.html
1166# Ignore objects and archives.
1167*.[oa]
1168-------------------------------------------------
1169
5162e697 1170See linkgit:gitignore[5] for a detailed explanation of the syntax. You can
464a8a7a
BF
1171also place .gitignore files in other directories in your working tree, and they
1172will apply to those directories and their subdirectories. The `.gitignore`
1173files can be added to your repository like any other files (just run `git add
1174.gitignore` and `git commit`, as usual), which is convenient when the exclude
1175patterns (such as patterns matching build output files) would also make sense
1176for other users who clone your repository.
1177
1178If you wish the exclude patterns to affect only certain repositories
1179(instead of every repository for a given project), you may instead put
1180them in a file in your repository named .git/info/exclude, or in any file
1181specified by the `core.excludesfile` configuration variable. Some git
1182commands can also take exclude patterns directly on the command line.
5162e697 1183See linkgit:gitignore[5] for the details.
2dc53617 1184
e34caace 1185[[how-to-merge]]
ae25c67a 1186How to merge
d19fbc3c
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1187------------
1188
1189You can rejoin two diverging branches of development using
5162e697 1190linkgit:git-merge[1]:
d19fbc3c
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1191
1192-------------------------------------------------
1193$ git merge branchname
1194-------------------------------------------------
1195
1196merges the development in the branch "branchname" into the current
e63ec003
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1197branch.
1198
1199A merge is made by combining the changes made in "branchname" and the
1200changes made up to the latest commit in your current branch since
1201their histories forked. The work tree is overwritten by the result of
1202the merge when this combining is done cleanly, or overwritten by a
1203half-merged results when this combining results in conflicts.
1204Therefore, if you have uncommitted changes touching the same files as
1205the ones impacted by the merge, Git will refuse to proceed. Most of
1206the time, you will want to commit your changes before you can merge,
1207and if you don't, then linkgit:git-stash[1] can take these changes
1208away while you're doing the merge, and reapply them afterwards.
1209
6a5d0b0a 1210If the changes are independent enough, Git will automatically complete
e63ec003
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1211the merge and commit the result (or reuse an existing commit in case
1212of <<fast-forwards,fast-forward>>, see below). On the other hand,
1213if there are conflicts--for example, if the same file is
d19fbc3c
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1214modified in two different ways in the remote branch and the local
1215branch--then you are warned; the output may look something like this:
1216
1217-------------------------------------------------
fabbd8f6
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1218$ git merge next
1219 100% (4/4) done
1220Auto-merged file.txt
d19fbc3c
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1221CONFLICT (content): Merge conflict in file.txt
1222Automatic merge failed; fix conflicts and then commit the result.
1223-------------------------------------------------
1224
1225Conflict markers are left in the problematic files, and after
1226you resolve the conflicts manually, you can update the index
1227with the contents and run git commit, as you normally would when
1228creating a new file.
1229
1230If you examine the resulting commit using gitk, you will see that it
1231has two parents, one pointing to the top of the current branch, and
1232one to the top of the other branch.
1233
d19fbc3c
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1234[[resolving-a-merge]]
1235Resolving a merge
1236-----------------
1237
1238When a merge isn't resolved automatically, git leaves the index and
1239the working tree in a special state that gives you all the
1240information you need to help resolve the merge.
1241
1242Files with conflicts are marked specially in the index, so until you
5162e697 1243resolve the problem and update the index, linkgit:git-commit[1] will
ef561ac7 1244fail:
d19fbc3c
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1245
1246-------------------------------------------------
1247$ git commit
1248file.txt: needs merge
1249-------------------------------------------------
1250
5162e697 1251Also, linkgit:git-status[1] will list those files as "unmerged", and the
ef561ac7
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1252files with conflicts will have conflict markers added, like this:
1253
1254-------------------------------------------------
1255<<<<<<< HEAD:file.txt
1256Hello world
1257=======
1258Goodbye
1259>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1260-------------------------------------------------
1261
1262All you need to do is edit the files to resolve the conflicts, and then
1263
1264-------------------------------------------------
1265$ git add file.txt
1266$ git commit
1267-------------------------------------------------
1268
1269Note that the commit message will already be filled in for you with
1270some information about the merge. Normally you can just use this
1271default message unchanged, but you may add additional commentary of
1272your own if desired.
1273
1274The above is all you need to know to resolve a simple merge. But git
1275also provides more information to help resolve conflicts:
1276
e34caace 1277[[conflict-resolution]]
ef561ac7
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1278Getting conflict-resolution help during a merge
1279~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
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1280
1281All of the changes that git was able to merge automatically are
5162e697 1282already added to the index file, so linkgit:git-diff[1] shows only
ef561ac7 1283the conflicts. It uses an unusual syntax:
d19fbc3c
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1284
1285-------------------------------------------------
1286$ git diff
1287diff --cc file.txt
1288index 802992c,2b60207..0000000
1289--- a/file.txt
1290+++ b/file.txt
1291@@@ -1,1 -1,1 +1,5 @@@
1292++<<<<<<< HEAD:file.txt
1293 +Hello world
1294++=======
1295+ Goodbye
1296++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1297-------------------------------------------------
1298
1130845b 1299Recall that the commit which will be committed after we resolve this
d19fbc3c
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1300conflict will have two parents instead of the usual one: one parent
1301will be HEAD, the tip of the current branch; the other will be the
1302tip of the other branch, which is stored temporarily in MERGE_HEAD.
1303
ef561ac7
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1304During the merge, the index holds three versions of each file. Each of
1305these three "file stages" represents a different version of the file:
1306
1307-------------------------------------------------
1308$ git show :1:file.txt # the file in a common ancestor of both branches
4209752d
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1309$ git show :2:file.txt # the version from HEAD.
1310$ git show :3:file.txt # the version from MERGE_HEAD.
ef561ac7
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1311-------------------------------------------------
1312
4209752d
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1313When you ask linkgit:git-diff[1] to show the conflicts, it runs a
1314three-way diff between the conflicted merge results in the work tree with
1315stages 2 and 3 to show only hunks whose contents come from both sides,
1316mixed (in other words, when a hunk's merge results come only from stage 2,
1317that part is not conflicting and is not shown. Same for stage 3).
ef561ac7
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1318
1319The diff above shows the differences between the working-tree version of
1320file.txt and the stage 2 and stage 3 versions. So instead of preceding
1321each line by a single "+" or "-", it now uses two columns: the first
1322column is used for differences between the first parent and the working
1323directory copy, and the second for differences between the second parent
1324and the working directory copy. (See the "COMBINED DIFF FORMAT" section
5162e697 1325of linkgit:git-diff-files[1] for a details of the format.)
ef561ac7
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1326
1327After resolving the conflict in the obvious way (but before updating the
1328index), the diff will look like:
d19fbc3c
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1329
1330-------------------------------------------------
1331$ git diff
1332diff --cc file.txt
1333index 802992c,2b60207..0000000
1334--- a/file.txt
1335+++ b/file.txt
1336@@@ -1,1 -1,1 +1,1 @@@
1337- Hello world
1338 -Goodbye
1339++Goodbye world
1340-------------------------------------------------
1341
1342This shows that our resolved version deleted "Hello world" from the
1343first parent, deleted "Goodbye" from the second parent, and added
1344"Goodbye world", which was previously absent from both.
1345
ef561ac7
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1346Some special diff options allow diffing the working directory against
1347any of these stages:
1348
1349-------------------------------------------------
1350$ git diff -1 file.txt # diff against stage 1
1351$ git diff --base file.txt # same as the above
1352$ git diff -2 file.txt # diff against stage 2
1353$ git diff --ours file.txt # same as the above
1354$ git diff -3 file.txt # diff against stage 3
1355$ git diff --theirs file.txt # same as the above.
1356-------------------------------------------------
1357
0cafe944 1358The linkgit:git-log[1] and linkgit:gitk[1] commands also provide special help
ef561ac7 1359for merges:
d19fbc3c
BF
1360
1361-------------------------------------------------
1362$ git log --merge
ef561ac7 1363$ gitk --merge
d19fbc3c
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1364-------------------------------------------------
1365
ef561ac7
BF
1366These will display all commits which exist only on HEAD or on
1367MERGE_HEAD, and which touch an unmerged file.
d19fbc3c 1368
5162e697 1369You may also use linkgit:git-mergetool[1], which lets you merge the
c7719fbe 1370unmerged files using external tools such as Emacs or kdiff3.
c64415e2 1371
ef561ac7 1372Each time you resolve the conflicts in a file and update the index:
d19fbc3c
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1373
1374-------------------------------------------------
1375$ git add file.txt
d19fbc3c
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1376-------------------------------------------------
1377
ef561ac7 1378the different stages of that file will be "collapsed", after which
6127c086 1379`git diff` will (by default) no longer show diffs for that file.
d19fbc3c
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1380
1381[[undoing-a-merge]]
ae25c67a 1382Undoing a merge
d19fbc3c
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1383---------------
1384
1385If you get stuck and decide to just give up and throw the whole mess
1386away, you can always return to the pre-merge state with
1387
1388-------------------------------------------------
1389$ git reset --hard HEAD
1390-------------------------------------------------
1391
1130845b 1392Or, if you've already committed the merge that you want to throw away,
d19fbc3c
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1393
1394-------------------------------------------------
1c73bb0e 1395$ git reset --hard ORIG_HEAD
d19fbc3c
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1396-------------------------------------------------
1397
1398However, this last command can be dangerous in some cases--never
1399throw away a commit you have already committed if that commit may
1400itself have been merged into another branch, as doing so may confuse
1401further merges.
1402
e34caace 1403[[fast-forwards]]
d19fbc3c
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1404Fast-forward merges
1405-------------------
1406
1407There is one special case not mentioned above, which is treated
1408differently. Normally, a merge results in a merge commit, with two
1409parents, one pointing at each of the two lines of development that
1410were merged.
1411
59723040
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1412However, if the current branch is a descendant of the other--so every
1413commit present in the one is already contained in the other--then git
a75d7b54 1414just performs a "fast-forward"; the head of the current branch is moved
59723040
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1415forward to point at the head of the merged-in branch, without any new
1416commits being created.
d19fbc3c 1417
e34caace 1418[[fixing-mistakes]]
b684f830
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1419Fixing mistakes
1420---------------
1421
1422If you've messed up the working tree, but haven't yet committed your
1423mistake, you can return the entire working tree to the last committed
1424state with
1425
1426-------------------------------------------------
1427$ git reset --hard HEAD
1428-------------------------------------------------
1429
1430If you make a commit that you later wish you hadn't, there are two
1431fundamentally different ways to fix the problem:
1432
1433 1. You can create a new commit that undoes whatever was done
93cbbd71 1434 by the old commit. This is the correct thing if your
b684f830
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1435 mistake has already been made public.
1436
1437 2. You can go back and modify the old commit. You should
1438 never do this if you have already made the history public;
1439 git does not normally expect the "history" of a project to
1440 change, and cannot correctly perform repeated merges from
1441 a branch that has had its history changed.
1442
e34caace 1443[[reverting-a-commit]]
b684f830
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1444Fixing a mistake with a new commit
1445~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1446
1447Creating a new commit that reverts an earlier change is very easy;
5162e697 1448just pass the linkgit:git-revert[1] command a reference to the bad
b684f830
BF
1449commit; for example, to revert the most recent commit:
1450
1451-------------------------------------------------
1452$ git revert HEAD
1453-------------------------------------------------
1454
1455This will create a new commit which undoes the change in HEAD. You
1456will be given a chance to edit the commit message for the new commit.
1457
1458You can also revert an earlier change, for example, the next-to-last:
1459
1460-------------------------------------------------
1461$ git revert HEAD^
1462-------------------------------------------------
1463
1464In this case git will attempt to undo the old change while leaving
1465intact any changes made since then. If more recent changes overlap
1466with the changes to be reverted, then you will be asked to fix
1467conflicts manually, just as in the case of <<resolving-a-merge,
1468resolving a merge>>.
1469
7cb192ea
BF
1470[[fixing-a-mistake-by-rewriting-history]]
1471Fixing a mistake by rewriting history
b684f830
BF
1472~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1473
1474If the problematic commit is the most recent commit, and you have not
1475yet made that commit public, then you may just
6127c086 1476<<undoing-a-merge,destroy it using `git reset`>>.
b684f830
BF
1477
1478Alternatively, you
1479can edit the working directory and update the index to fix your
1480mistake, just as if you were going to <<how-to-make-a-commit,create a
1481new commit>>, then run
1482
1483-------------------------------------------------
1484$ git commit --amend
1485-------------------------------------------------
1486
1487which will replace the old commit by a new commit incorporating your
1488changes, giving you a chance to edit the old commit message first.
1489
1490Again, you should never do this to a commit that may already have
5162e697 1491been merged into another branch; use linkgit:git-revert[1] instead in
b684f830
BF
1492that case.
1493
7cb192ea 1494It is also possible to replace commits further back in the history, but
b684f830
BF
1495this is an advanced topic to be left for
1496<<cleaning-up-history,another chapter>>.
1497
e34caace 1498[[checkout-of-path]]
b684f830
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1499Checking out an old version of a file
1500~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1501
1502In the process of undoing a previous bad change, you may find it
1503useful to check out an older version of a particular file using
6127c086 1504linkgit:git-checkout[1]. We've used `git checkout` before to switch
b684f830
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1505branches, but it has quite different behavior if it is given a path
1506name: the command
1507
1508-------------------------------------------------
1509$ git checkout HEAD^ path/to/file
1510-------------------------------------------------
1511
1512replaces path/to/file by the contents it had in the commit HEAD^, and
1513also updates the index to match. It does not change branches.
1514
1515If you just want to look at an old version of the file, without
1516modifying the working directory, you can do that with
5162e697 1517linkgit:git-show[1]:
b684f830
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1518
1519-------------------------------------------------
ed4eb0d8 1520$ git show HEAD^:path/to/file
b684f830
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1521-------------------------------------------------
1522
1523which will display the given version of the file.
1524
7a7cc594
JH
1525[[interrupted-work]]
1526Temporarily setting aside work in progress
1527~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1528
1529While you are in the middle of working on something complicated, you
1530find an unrelated but obvious and trivial bug. You would like to fix it
5162e697 1531before continuing. You can use linkgit:git-stash[1] to save the current
7a7cc594
JH
1532state of your work, and after fixing the bug (or, optionally after doing
1533so on a different branch and then coming back), unstash the
1534work-in-progress changes.
1535
1536------------------------------------------------
7a85f6ae 1537$ git stash save "work in progress for foo feature"
7a7cc594
JH
1538------------------------------------------------
1539
1540This command will save your changes away to the `stash`, and
1541reset your working tree and the index to match the tip of your
1542current branch. Then you can make your fix as usual.
1543
1544------------------------------------------------
1545... edit and test ...
1546$ git commit -a -m "blorpl: typofix"
1547------------------------------------------------
1548
1549After that, you can go back to what you were working on with
7b8988e1 1550`git stash pop`:
7a7cc594
JH
1551
1552------------------------------------------------
7b8988e1 1553$ git stash pop
7a7cc594
JH
1554------------------------------------------------
1555
1556
e34caace 1557[[ensuring-good-performance]]
d19fbc3c
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1558Ensuring good performance
1559-------------------------
1560
1561On large repositories, git depends on compression to keep the history
06ada152 1562information from taking up too much space on disk or in memory.
d19fbc3c
BF
1563
1564This compression is not performed automatically. Therefore you
5162e697 1565should occasionally run linkgit:git-gc[1]:
d19fbc3c
BF
1566
1567-------------------------------------------------
1568$ git gc
1569-------------------------------------------------
1570
17217090 1571to recompress the archive. This can be very time-consuming, so
6127c086 1572you may prefer to run `git gc` when you are not doing other work.
d19fbc3c 1573
e34caace
BF
1574
1575[[ensuring-reliability]]
11e016a3
BF
1576Ensuring reliability
1577--------------------
1578
e34caace 1579[[checking-for-corruption]]
11e016a3
BF
1580Checking the repository for corruption
1581~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1582
5162e697 1583The linkgit:git-fsck[1] command runs a number of self-consistency checks
1191ee18 1584on the repository, and reports on any problems. This may take some
21dcb3b7
BF
1585time. The most common warning by far is about "dangling" objects:
1586
1587-------------------------------------------------
04e50e94 1588$ git fsck
21dcb3b7
BF
1589dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1590dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1591dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1592dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1593dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1594dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1595dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1596dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1597...
1598-------------------------------------------------
1599
59723040 1600Dangling objects are not a problem. At worst they may take up a little
54782859 1601extra disk space. They can sometimes provide a last-resort method for
208641cf 1602recovering lost work--see <<dangling-objects>> for details.
1cdade2c 1603
e34caace 1604[[recovering-lost-changes]]
11e016a3
BF
1605Recovering lost changes
1606~~~~~~~~~~~~~~~~~~~~~~~
1607
e34caace 1608[[reflogs]]
559e4d7a
BF
1609Reflogs
1610^^^^^^^
1611
5162e697 1612Say you modify a branch with `linkgit:git-reset[1] --hard`, and then
559e4d7a
BF
1613realize that the branch was the only reference you had to that point in
1614history.
1615
1616Fortunately, git also keeps a log, called a "reflog", of all the
1617previous values of each branch. So in this case you can still find the
a6080a0a 1618old history using, for example,
559e4d7a
BF
1619
1620-------------------------------------------------
1621$ git log master@{1}
1622-------------------------------------------------
1623
e502c2c3
SO
1624This lists the commits reachable from the previous version of the
1625"master" branch head. This syntax can be used with any git command
1626that accepts a commit, not just with git log. Some other examples:
559e4d7a
BF
1627
1628-------------------------------------------------
1629$ git show master@{2} # See where the branch pointed 2,
1630$ git show master@{3} # 3, ... changes ago.
1631$ gitk master@{yesterday} # See where it pointed yesterday,
1632$ gitk master@{"1 week ago"} # ... or last week
953f3d6f
BF
1633$ git log --walk-reflogs master # show reflog entries for master
1634-------------------------------------------------
1635
1636A separate reflog is kept for the HEAD, so
1637
1638-------------------------------------------------
1639$ git show HEAD@{"1 week ago"}
559e4d7a
BF
1640-------------------------------------------------
1641
953f3d6f
BF
1642will show what HEAD pointed to one week ago, not what the current branch
1643pointed to one week ago. This allows you to see the history of what
1644you've checked out.
1645
559e4d7a 1646The reflogs are kept by default for 30 days, after which they may be
5162e697 1647pruned. See linkgit:git-reflog[1] and linkgit:git-gc[1] to learn
559e4d7a 1648how to control this pruning, and see the "SPECIFYING REVISIONS"
9d83e382 1649section of linkgit:gitrevisions[7] for details.
559e4d7a
BF
1650
1651Note that the reflog history is very different from normal git history.
1652While normal history is shared by every repository that works on the
1653same project, the reflog history is not shared: it tells you only about
1654how the branches in your local repository have changed over time.
1655
59723040 1656[[dangling-object-recovery]]
559e4d7a
BF
1657Examining dangling objects
1658^^^^^^^^^^^^^^^^^^^^^^^^^^
1659
59723040
BF
1660In some situations the reflog may not be able to save you. For example,
1661suppose you delete a branch, then realize you need the history it
1662contained. The reflog is also deleted; however, if you have not yet
1663pruned the repository, then you may still be able to find the lost
6127c086 1664commits in the dangling objects that `git fsck` reports. See
59723040 1665<<dangling-objects>> for the details.
559e4d7a
BF
1666
1667-------------------------------------------------
1668$ git fsck
1669dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1670dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1671dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1672...
1673-------------------------------------------------
1674
aacd404e 1675You can examine
559e4d7a
BF
1676one of those dangling commits with, for example,
1677
1678------------------------------------------------
1679$ gitk 7281251ddd --not --all
1680------------------------------------------------
1681
1682which does what it sounds like: it says that you want to see the commit
1683history that is described by the dangling commit(s), but not the
1684history that is described by all your existing branches and tags. Thus
1685you get exactly the history reachable from that commit that is lost.
1686(And notice that it might not be just one commit: we only report the
1687"tip of the line" as being dangling, but there might be a whole deep
79c96c57 1688and complex commit history that was dropped.)
559e4d7a
BF
1689
1690If you decide you want the history back, you can always create a new
1691reference pointing to it, for example, a new branch:
1692
1693------------------------------------------------
a6080a0a 1694$ git branch recovered-branch 7281251ddd
559e4d7a
BF
1695------------------------------------------------
1696
59723040
BF
1697Other types of dangling objects (blobs and trees) are also possible, and
1698dangling objects can arise in other situations.
1699
11e016a3 1700
e34caace 1701[[sharing-development]]
d19fbc3c 1702Sharing development with others
b684f830 1703===============================
d19fbc3c 1704
aa971cb9 1705[[getting-updates-With-git-pull]]
6127c086 1706Getting updates with git pull
b684f830 1707-----------------------------
d19fbc3c 1708
e63ec003 1709After you clone a repository and commit a few changes of your own, you
d19fbc3c
BF
1710may wish to check the original repository for updates and merge them
1711into your own work.
1712
aa971cb9 1713We have already seen <<Updating-a-repository-With-git-fetch,how to
0e615b25 1714keep remote-tracking branches up to date>> with linkgit:git-fetch[1],
d19fbc3c
BF
1715and how to merge two branches. So you can merge in changes from the
1716original repository's master branch with:
1717
1718-------------------------------------------------
1719$ git fetch
1720$ git merge origin/master
1721-------------------------------------------------
1722
5162e697 1723However, the linkgit:git-pull[1] command provides a way to do this in
d19fbc3c
BF
1724one step:
1725
1726-------------------------------------------------
1727$ git pull origin master
1728-------------------------------------------------
1729
66a062a1
MM
1730In fact, if you have "master" checked out, then this branch has been
1731configured by "git clone" to get changes from the HEAD branch of the
1732origin repository. So often you can
0eb4f7cd 1733accomplish the above with just a simple
d19fbc3c
BF
1734
1735-------------------------------------------------
1736$ git pull
1737-------------------------------------------------
1738
66a062a1
MM
1739This command will fetch changes from the remote branches to your
1740remote-tracking branches `origin/*`, and merge the default branch into
1741the current branch.
1742
29b9a66f
MM
1743More generally, a branch that is created from a remote-tracking branch
1744will pull
0eb4f7cd
BF
1745by default from that branch. See the descriptions of the
1746branch.<name>.remote and branch.<name>.merge options in
5162e697
DM
1747linkgit:git-config[1], and the discussion of the `--track` option in
1748linkgit:git-checkout[1], to learn how to control these defaults.
d19fbc3c
BF
1749
1750In addition to saving you keystrokes, "git pull" also helps you by
1751producing a default commit message documenting the branch and
1752repository that you pulled from.
1753
1754(But note that no such commit will be created in the case of a
a75d7b54 1755<<fast-forwards,fast-forward>>; instead, your branch will just be
79c96c57 1756updated to point to the latest commit from the upstream branch.)
d19fbc3c 1757
6127c086 1758The `git pull` command can also be given "." as the "remote" repository,
1191ee18 1759in which case it just merges in a branch from the current repository; so
4c63ff45
BF
1760the commands
1761
1762-------------------------------------------------
1763$ git pull . branch
1764$ git merge branch
1765-------------------------------------------------
1766
1767are roughly equivalent. The former is actually very commonly used.
1768
e34caace 1769[[submitting-patches]]
d19fbc3c 1770Submitting patches to a project
b684f830 1771-------------------------------
d19fbc3c
BF
1772
1773If you just have a few changes, the simplest way to submit them may
1774just be to send them as patches in email:
1775
5162e697 1776First, use linkgit:git-format-patch[1]; for example:
d19fbc3c
BF
1777
1778-------------------------------------------------
eb6ae7f4 1779$ git format-patch origin
d19fbc3c
BF
1780-------------------------------------------------
1781
1782will produce a numbered series of files in the current directory, one
1783for each patch in the current branch but not in origin/HEAD.
1784
1785You can then import these into your mail client and send them by
1786hand. However, if you have a lot to send at once, you may prefer to
5162e697 1787use the linkgit:git-send-email[1] script to automate the process.
d19fbc3c
BF
1788Consult the mailing list for your project first to determine how they
1789prefer such patches be handled.
1790
e34caace 1791[[importing-patches]]
d19fbc3c 1792Importing patches to a project
b684f830 1793------------------------------
d19fbc3c 1794
5162e697 1795Git also provides a tool called linkgit:git-am[1] (am stands for
d19fbc3c
BF
1796"apply mailbox"), for importing such an emailed series of patches.
1797Just save all of the patch-containing messages, in order, into a
1798single mailbox file, say "patches.mbox", then run
1799
1800-------------------------------------------------
eb6ae7f4 1801$ git am -3 patches.mbox
d19fbc3c
BF
1802-------------------------------------------------
1803
1804Git will apply each patch in order; if any conflicts are found, it
1805will stop, and you can fix the conflicts as described in
01997b4a
BF
1806"<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells
1807git to perform a merge; if you would prefer it just to abort and
1808leave your tree and index untouched, you may omit that option.)
1809
1810Once the index is updated with the results of the conflict
1811resolution, instead of creating a new commit, just run
d19fbc3c
BF
1812
1813-------------------------------------------------
1814$ git am --resolved
1815-------------------------------------------------
1816
1817and git will create the commit for you and continue applying the
1818remaining patches from the mailbox.
1819
1820The final result will be a series of commits, one for each patch in
1821the original mailbox, with authorship and commit log message each
1822taken from the message containing each patch.
1823
eda69449
BF
1824[[public-repositories]]
1825Public git repositories
1826-----------------------
d19fbc3c 1827
6e30fb0c
DK
1828Another way to submit changes to a project is to tell the maintainer
1829of that project to pull the changes from your repository using
aa971cb9 1830linkgit:git-pull[1]. In the section "<<getting-updates-With-git-pull,
6127c086 1831Getting updates with `git pull`>>" we described this as a way to get
6e30fb0c
DK
1832updates from the "main" repository, but it works just as well in the
1833other direction.
d19fbc3c 1834
eda69449
BF
1835If you and the maintainer both have accounts on the same machine, then
1836you can just pull changes from each other's repositories directly;
11d51533 1837commands that accept repository URLs as arguments will also accept a
eda69449 1838local directory name:
d19fbc3c
BF
1839
1840-------------------------------------------------
1841$ git clone /path/to/repository
1842$ git pull /path/to/other/repository
1843-------------------------------------------------
1844
c9016158 1845or an ssh URL:
11d51533
BF
1846
1847-------------------------------------------------
1848$ git clone ssh://yourhost/~you/repository
1849-------------------------------------------------
1850
1851For projects with few developers, or for synchronizing a few private
1852repositories, this may be all you need.
1853
eda69449
BF
1854However, the more common way to do this is to maintain a separate public
1855repository (usually on a different host) for others to pull changes
1856from. This is usually more convenient, and allows you to cleanly
1857separate private work in progress from publicly visible work.
d19fbc3c
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1858
1859You will continue to do your day-to-day work in your personal
1860repository, but periodically "push" changes from your personal
1861repository into your public repository, allowing other developers to
1862pull from that repository. So the flow of changes, in a situation
1863where there is one other developer with a public repository, looks
1864like this:
1865
1866 you push
1867 your personal repo ------------------> your public repo
a6080a0a 1868 ^ |
d19fbc3c
BF
1869 | |
1870 | you pull | they pull
1871 | |
1872 | |
1873 | they push V
1874 their public repo <------------------- their repo
1875
11d51533
BF
1876We explain how to do this in the following sections.
1877
eda69449
BF
1878[[setting-up-a-public-repository]]
1879Setting up a public repository
1880~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1881
1882Assume your personal repository is in the directory ~/proj. We
6127c086 1883first create a new clone of the repository and tell `git daemon` that it
eda69449 1884is meant to be public:
d19fbc3c
BF
1885
1886-------------------------------------------------
52c80037 1887$ git clone --bare ~/proj proj.git
eda69449 1888$ touch proj.git/git-daemon-export-ok
d19fbc3c
BF
1889-------------------------------------------------
1890
52c80037 1891The resulting directory proj.git contains a "bare" git repository--it is
eda69449
BF
1892just the contents of the ".git" directory, without any files checked out
1893around it.
d19fbc3c 1894
c64415e2 1895Next, copy proj.git to the server where you plan to host the
d19fbc3c
BF
1896public repository. You can use scp, rsync, or whatever is most
1897convenient.
1898
eda69449
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1899[[exporting-via-git]]
1900Exporting a git repository via the git protocol
1901~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1902
1903This is the preferred method.
1904
1905If someone else administers the server, they should tell you what
c9016158 1906directory to put the repository in, and what git:// URL it will appear
eda69449 1907at. You can then skip to the section
d19fbc3c
BF
1908"<<pushing-changes-to-a-public-repository,Pushing changes to a public
1909repository>>", below.
1910
5162e697 1911Otherwise, all you need to do is start linkgit:git-daemon[1]; it will
eda69449
BF
1912listen on port 9418. By default, it will allow access to any directory
1913that looks like a git directory and contains the magic file
6127c086 1914git-daemon-export-ok. Passing some directory paths as `git daemon`
eda69449
BF
1915arguments will further restrict the exports to those paths.
1916
6127c086 1917You can also run `git daemon` as an inetd service; see the
5162e697 1918linkgit:git-daemon[1] man page for details. (See especially the
eda69449 1919examples section.)
d19fbc3c
BF
1920
1921[[exporting-via-http]]
1922Exporting a git repository via http
eda69449 1923~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
1924
1925The git protocol gives better performance and reliability, but on a
1926host with a web server set up, http exports may be simpler to set up.
1927
1928All you need to do is place the newly created bare git repository in
1929a directory that is exported by the web server, and make some
1930adjustments to give web clients some extra information they need:
1931
1932-------------------------------------------------
1933$ mv proj.git /home/you/public_html/proj.git
1934$ cd proj.git
c64415e2 1935$ git --bare update-server-info
7dce9918 1936$ mv hooks/post-update.sample hooks/post-update
d19fbc3c
BF
1937-------------------------------------------------
1938
1939(For an explanation of the last two lines, see
6998e4db 1940linkgit:git-update-server-info[1] and linkgit:githooks[5].)
d19fbc3c 1941
c9016158
RW
1942Advertise the URL of proj.git. Anybody else should then be able to
1943clone or pull from that URL, for example with a command line like:
d19fbc3c
BF
1944
1945-------------------------------------------------
1946$ git clone http://yourserver.com/~you/proj.git
1947-------------------------------------------------
1948
1949(See also
1950link:howto/setup-git-server-over-http.txt[setup-git-server-over-http]
1951for a slightly more sophisticated setup using WebDAV which also
1952allows pushing over http.)
1953
d19fbc3c
BF
1954[[pushing-changes-to-a-public-repository]]
1955Pushing changes to a public repository
eda69449 1956~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 1957
eda69449 1958Note that the two techniques outlined above (exporting via
d19fbc3c
BF
1959<<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other
1960maintainers to fetch your latest changes, but they do not allow write
1961access, which you will need to update the public repository with the
1962latest changes created in your private repository.
1963
5162e697 1964The simplest way to do this is using linkgit:git-push[1] and ssh; to
d19fbc3c
BF
1965update the remote branch named "master" with the latest state of your
1966branch named "master", run
1967
1968-------------------------------------------------
1969$ git push ssh://yourserver.com/~you/proj.git master:master
1970-------------------------------------------------
1971
1972or just
1973
1974-------------------------------------------------
1975$ git push ssh://yourserver.com/~you/proj.git master
1976-------------------------------------------------
1977
6127c086 1978As with `git fetch`, `git push` will complain if this does not result in a
a75d7b54 1979<<fast-forwards,fast-forward>>; see the following section for details on
81eb417a 1980handling this case.
d19fbc3c 1981
11d51533
BF
1982Note that the target of a "push" is normally a
1983<<def_bare_repository,bare>> repository. You can also push to a
1984repository that has a checked-out working tree, but the working tree
1985will not be updated by the push. This may lead to unexpected results if
1986the branch you push to is the currently checked-out branch!
1987
6127c086 1988As with `git fetch`, you may also set up configuration options to
d19fbc3c
BF
1989save typing; so, for example, after
1990
1991-------------------------------------------------
c64415e2 1992$ cat >>.git/config <<EOF
d19fbc3c
BF
1993[remote "public-repo"]
1994 url = ssh://yourserver.com/~you/proj.git
1995EOF
1996-------------------------------------------------
1997
1998you should be able to perform the above push with just
1999
2000-------------------------------------------------
2001$ git push public-repo master
2002-------------------------------------------------
2003
2004See the explanations of the remote.<name>.url, branch.<name>.remote,
5162e697 2005and remote.<name>.push options in linkgit:git-config[1] for
d19fbc3c
BF
2006details.
2007
81eb417a
BF
2008[[forcing-push]]
2009What to do when a push fails
2010~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2011
a75d7b54 2012If a push would not result in a <<fast-forwards,fast-forward>> of the
81eb417a
BF
2013remote branch, then it will fail with an error like:
2014
2015-------------------------------------------------
2016error: remote 'refs/heads/master' is not an ancestor of
2017 local 'refs/heads/master'.
2018 Maybe you are not up-to-date and need to pull first?
2019error: failed to push to 'ssh://yourserver.com/~you/proj.git'
2020-------------------------------------------------
2021
2022This can happen, for example, if you:
2023
6127c086
FC
2024 - use `git reset --hard` to remove already-published commits, or
2025 - use `git commit --amend` to replace already-published commits
7cb192ea 2026 (as in <<fixing-a-mistake-by-rewriting-history>>), or
6127c086 2027 - use `git rebase` to rebase any already-published commits (as
81eb417a
BF
2028 in <<using-git-rebase>>).
2029
6127c086 2030You may force `git push` to perform the update anyway by preceding the
81eb417a
BF
2031branch name with a plus sign:
2032
2033-------------------------------------------------
2034$ git push ssh://yourserver.com/~you/proj.git +master
2035-------------------------------------------------
2036
2037Normally whenever a branch head in a public repository is modified, it
9e5d87d4 2038is modified to point to a descendant of the commit that it pointed to
81eb417a 2039before. By forcing a push in this situation, you break that convention.
aa971cb9 2040(See <<problems-With-rewriting-history>>.)
81eb417a
BF
2041
2042Nevertheless, this is a common practice for people that need a simple
2043way to publish a work-in-progress patch series, and it is an acceptable
2044compromise as long as you warn other developers that this is how you
2045intend to manage the branch.
2046
2047It's also possible for a push to fail in this way when other people have
2048the right to push to the same repository. In that case, the correct
843c81dc
EH
2049solution is to retry the push after first updating your work: either by a
2050pull, or by a fetch followed by a rebase; see the
81eb417a 2051<<setting-up-a-shared-repository,next section>> and
6998e4db 2052linkgit:gitcvs-migration[7] for more.
81eb417a 2053
e34caace 2054[[setting-up-a-shared-repository]]
d19fbc3c 2055Setting up a shared repository
eda69449 2056~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
2057
2058Another way to collaborate is by using a model similar to that
2059commonly used in CVS, where several developers with special rights
2060all push to and pull from a single shared repository. See
6998e4db 2061linkgit:gitcvs-migration[7] for instructions on how to
d19fbc3c
BF
2062set this up.
2063
8fae2225
BF
2064However, while there is nothing wrong with git's support for shared
2065repositories, this mode of operation is not generally recommended,
2066simply because the mode of collaboration that git supports--by
2067exchanging patches and pulling from public repositories--has so many
2068advantages over the central shared repository:
2069
2070 - Git's ability to quickly import and merge patches allows a
2071 single maintainer to process incoming changes even at very
6127c086 2072 high rates. And when that becomes too much, `git pull` provides
8fae2225
BF
2073 an easy way for that maintainer to delegate this job to other
2074 maintainers while still allowing optional review of incoming
2075 changes.
2076 - Since every developer's repository has the same complete copy
2077 of the project history, no repository is special, and it is
2078 trivial for another developer to take over maintenance of a
2079 project, either by mutual agreement, or because a maintainer
2080 becomes unresponsive or difficult to work with.
2081 - The lack of a central group of "committers" means there is
2082 less need for formal decisions about who is "in" and who is
2083 "out".
2084
e34caace 2085[[setting-up-gitweb]]
eda69449
BF
2086Allowing web browsing of a repository
2087~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 2088
a8cd1402
BF
2089The gitweb cgi script provides users an easy way to browse your
2090project's files and history without having to install git; see the file
04483524 2091gitweb/INSTALL in the git source tree for instructions on setting it up.
d19fbc3c 2092
e34caace 2093[[sharing-development-examples]]
b684f830
BF
2094Examples
2095--------
d19fbc3c 2096
9e2163ea
BF
2097[[maintaining-topic-branches]]
2098Maintaining topic branches for a Linux subsystem maintainer
2099~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2100
2101This describes how Tony Luck uses git in his role as maintainer of the
2102IA64 architecture for the Linux kernel.
2103
2104He uses two public branches:
2105
2106 - A "test" tree into which patches are initially placed so that they
2107 can get some exposure when integrated with other ongoing development.
2108 This tree is available to Andrew for pulling into -mm whenever he
2109 wants.
2110
2111 - A "release" tree into which tested patches are moved for final sanity
2112 checking, and as a vehicle to send them upstream to Linus (by sending
2113 him a "please pull" request.)
2114
2115He also uses a set of temporary branches ("topic branches"), each
2116containing a logical grouping of patches.
2117
2118To set this up, first create your work tree by cloning Linus's public
2119tree:
2120
2121-------------------------------------------------
2122$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work
2123$ cd work
2124-------------------------------------------------
2125
29b9a66f 2126Linus's tree will be stored in the remote-tracking branch named origin/master,
5162e697
DM
2127and can be updated using linkgit:git-fetch[1]; you can track other
2128public trees using linkgit:git-remote[1] to set up a "remote" and
2129linkgit:git-fetch[1] to keep them up-to-date; see
6e30fb0c 2130<<repositories-and-branches>>.
9e2163ea
BF
2131
2132Now create the branches in which you are going to work; these start out
2133at the current tip of origin/master branch, and should be set up (using
5162e697 2134the --track option to linkgit:git-branch[1]) to merge changes in from
9e2163ea
BF
2135Linus by default.
2136
2137-------------------------------------------------
2138$ git branch --track test origin/master
2139$ git branch --track release origin/master
2140-------------------------------------------------
2141
5162e697 2142These can be easily kept up to date using linkgit:git-pull[1].
9e2163ea
BF
2143
2144-------------------------------------------------
2145$ git checkout test && git pull
2146$ git checkout release && git pull
2147-------------------------------------------------
2148
2149Important note! If you have any local changes in these branches, then
2150this merge will create a commit object in the history (with no local
a75d7b54 2151changes git will simply do a "fast-forward" merge). Many people dislike
9e2163ea
BF
2152the "noise" that this creates in the Linux history, so you should avoid
2153doing this capriciously in the "release" branch, as these noisy commits
2154will become part of the permanent history when you ask Linus to pull
2155from the release branch.
2156
5162e697 2157A few configuration variables (see linkgit:git-config[1]) can
9e2163ea
BF
2158make it easy to push both branches to your public tree. (See
2159<<setting-up-a-public-repository>>.)
2160
2161-------------------------------------------------
2162$ cat >> .git/config <<EOF
2163[remote "mytree"]
2164 url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
2165 push = release
2166 push = test
2167EOF
2168-------------------------------------------------
2169
2170Then you can push both the test and release trees using
5162e697 2171linkgit:git-push[1]:
9e2163ea
BF
2172
2173-------------------------------------------------
2174$ git push mytree
2175-------------------------------------------------
2176
2177or push just one of the test and release branches using:
2178
2179-------------------------------------------------
2180$ git push mytree test
2181-------------------------------------------------
2182
2183or
2184
2185-------------------------------------------------
2186$ git push mytree release
2187-------------------------------------------------
2188
2189Now to apply some patches from the community. Think of a short
2190snappy name for a branch to hold this patch (or related group of
352953a5
TL
2191patches), and create a new branch from a recent stable tag of
2192Linus's branch. Picking a stable base for your branch will:
21931) help you: by avoiding inclusion of unrelated and perhaps lightly
2194tested changes
21952) help future bug hunters that use "git bisect" to find problems
9e2163ea
BF
2196
2197-------------------------------------------------
352953a5 2198$ git checkout -b speed-up-spinlocks v2.6.35
9e2163ea
BF
2199-------------------------------------------------
2200
2201Now you apply the patch(es), run some tests, and commit the change(s). If
2202the patch is a multi-part series, then you should apply each as a separate
2203commit to this branch.
2204
2205-------------------------------------------------
2206$ ... patch ... test ... commit [ ... patch ... test ... commit ]*
2207-------------------------------------------------
2208
2209When you are happy with the state of this change, you can pull it into the
2210"test" branch in preparation to make it public:
2211
2212-------------------------------------------------
2213$ git checkout test && git pull . speed-up-spinlocks
2214-------------------------------------------------
2215
2216It is unlikely that you would have any conflicts here ... but you might if you
2217spent a while on this step and had also pulled new versions from upstream.
2218
2219Some time later when enough time has passed and testing done, you can pull the
2220same branch into the "release" tree ready to go upstream. This is where you
2221see the value of keeping each patch (or patch series) in its own branch. It
2222means that the patches can be moved into the "release" tree in any order.
2223
2224-------------------------------------------------
2225$ git checkout release && git pull . speed-up-spinlocks
2226-------------------------------------------------
2227
2228After a while, you will have a number of branches, and despite the
2229well chosen names you picked for each of them, you may forget what
2230they are for, or what status they are in. To get a reminder of what
2231changes are in a specific branch, use:
2232
2233-------------------------------------------------
467c0197 2234$ git log linux..branchname | git shortlog
9e2163ea
BF
2235-------------------------------------------------
2236
06ada152 2237To see whether it has already been merged into the test or release branches,
9e2163ea
BF
2238use:
2239
2240-------------------------------------------------
2241$ git log test..branchname
2242-------------------------------------------------
2243
2244or
2245
2246-------------------------------------------------
2247$ git log release..branchname
2248-------------------------------------------------
2249
06ada152 2250(If this branch has not yet been merged, you will see some log entries.
9e2163ea
BF
2251If it has been merged, then there will be no output.)
2252
2253Once a patch completes the great cycle (moving from test to release,
2254then pulled by Linus, and finally coming back into your local
06ada152 2255"origin/master" branch), the branch for this change is no longer needed.
9e2163ea
BF
2256You detect this when the output from:
2257
2258-------------------------------------------------
2259$ git log origin..branchname
2260-------------------------------------------------
2261
2262is empty. At this point the branch can be deleted:
2263
2264-------------------------------------------------
2265$ git branch -d branchname
2266-------------------------------------------------
2267
2268Some changes are so trivial that it is not necessary to create a separate
2269branch and then merge into each of the test and release branches. For
2270these changes, just apply directly to the "release" branch, and then
2271merge that into the "test" branch.
2272
2273To create diffstat and shortlog summaries of changes to include in a "please
2274pull" request to Linus you can use:
2275
2276-------------------------------------------------
2277$ git diff --stat origin..release
2278-------------------------------------------------
2279
2280and
2281
2282-------------------------------------------------
2283$ git log -p origin..release | git shortlog
2284-------------------------------------------------
2285
2286Here are some of the scripts that simplify all this even further.
2287
2288-------------------------------------------------
2289==== update script ====
2290# Update a branch in my GIT tree. If the branch to be updated
2291# is origin, then pull from kernel.org. Otherwise merge
2292# origin/master branch into test|release branch
2293
2294case "$1" in
2295test|release)
2296 git checkout $1 && git pull . origin
2297 ;;
2298origin)
fc74ecc1 2299 before=$(git rev-parse refs/remotes/origin/master)
9e2163ea 2300 git fetch origin
fc74ecc1 2301 after=$(git rev-parse refs/remotes/origin/master)
9e2163ea
BF
2302 if [ $before != $after ]
2303 then
2304 git log $before..$after | git shortlog
2305 fi
2306 ;;
2307*)
2308 echo "Usage: $0 origin|test|release" 1>&2
2309 exit 1
2310 ;;
2311esac
2312-------------------------------------------------
2313
2314-------------------------------------------------
2315==== merge script ====
2316# Merge a branch into either the test or release branch
2317
2318pname=$0
2319
2320usage()
2321{
2322 echo "Usage: $pname branch test|release" 1>&2
2323 exit 1
2324}
2325
fc74ecc1 2326git show-ref -q --verify -- refs/heads/"$1" || {
9e2163ea
BF
2327 echo "Can't see branch <$1>" 1>&2
2328 usage
fc74ecc1 2329}
9e2163ea
BF
2330
2331case "$2" in
2332test|release)
2333 if [ $(git log $2..$1 | wc -c) -eq 0 ]
2334 then
2335 echo $1 already merged into $2 1>&2
2336 exit 1
2337 fi
2338 git checkout $2 && git pull . $1
2339 ;;
2340*)
2341 usage
2342 ;;
2343esac
2344-------------------------------------------------
2345
2346-------------------------------------------------
2347==== status script ====
2348# report on status of my ia64 GIT tree
2349
2350gb=$(tput setab 2)
2351rb=$(tput setab 1)
2352restore=$(tput setab 9)
2353
2354if [ `git rev-list test..release | wc -c` -gt 0 ]
2355then
2356 echo $rb Warning: commits in release that are not in test $restore
2357 git log test..release
2358fi
2359
fc74ecc1 2360for branch in `git show-ref --heads | sed 's|^.*/||'`
9e2163ea
BF
2361do
2362 if [ $branch = test -o $branch = release ]
2363 then
2364 continue
2365 fi
2366
2367 echo -n $gb ======= $branch ====== $restore " "
2368 status=
2369 for ref in test release origin/master
2370 do
2371 if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]
2372 then
2373 status=$status${ref:0:1}
2374 fi
2375 done
2376 case $status in
2377 trl)
2378 echo $rb Need to pull into test $restore
2379 ;;
2380 rl)
2381 echo "In test"
2382 ;;
2383 l)
2384 echo "Waiting for linus"
2385 ;;
2386 "")
2387 echo $rb All done $restore
2388 ;;
2389 *)
2390 echo $rb "<$status>" $restore
2391 ;;
2392 esac
2393 git log origin/master..$branch | git shortlog
2394done
2395-------------------------------------------------
d19fbc3c 2396
d19fbc3c 2397
d19fbc3c 2398[[cleaning-up-history]]
4c63ff45
BF
2399Rewriting history and maintaining patch series
2400==============================================
2401
2402Normally commits are only added to a project, never taken away or
2403replaced. Git is designed with this assumption, and violating it will
2404cause git's merge machinery (for example) to do the wrong thing.
2405
2406However, there is a situation in which it can be useful to violate this
2407assumption.
2408
e34caace 2409[[patch-series]]
4c63ff45
BF
2410Creating the perfect patch series
2411---------------------------------
2412
2413Suppose you are a contributor to a large project, and you want to add a
2414complicated feature, and to present it to the other developers in a way
2415that makes it easy for them to read your changes, verify that they are
2416correct, and understand why you made each change.
2417
b181d57f 2418If you present all of your changes as a single patch (or commit), they
79c96c57 2419may find that it is too much to digest all at once.
4c63ff45
BF
2420
2421If you present them with the entire history of your work, complete with
2422mistakes, corrections, and dead ends, they may be overwhelmed.
2423
2424So the ideal is usually to produce a series of patches such that:
2425
2426 1. Each patch can be applied in order.
2427
2428 2. Each patch includes a single logical change, together with a
2429 message explaining the change.
2430
2431 3. No patch introduces a regression: after applying any initial
2432 part of the series, the resulting project still compiles and
2433 works, and has no bugs that it didn't have before.
2434
2435 4. The complete series produces the same end result as your own
2436 (probably much messier!) development process did.
2437
b181d57f
BF
2438We will introduce some tools that can help you do this, explain how to
2439use them, and then explain some of the problems that can arise because
2440you are rewriting history.
4c63ff45 2441
e34caace 2442[[using-git-rebase]]
6127c086 2443Keeping a patch series up to date using git rebase
4c63ff45
BF
2444--------------------------------------------------
2445
79c96c57
MC
2446Suppose that you create a branch "mywork" on a remote-tracking branch
2447"origin", and create some commits on top of it:
4c63ff45
BF
2448
2449-------------------------------------------------
2450$ git checkout -b mywork origin
2451$ vi file.txt
2452$ git commit
2453$ vi otherfile.txt
2454$ git commit
2455...
2456-------------------------------------------------
2457
2458You have performed no merges into mywork, so it is just a simple linear
2459sequence of patches on top of "origin":
2460
1dc71a91 2461................................................
fa8347b8 2462 o--o--O <-- origin
4c63ff45 2463 \
fa8347b8 2464 a--b--c <-- mywork
1dc71a91 2465................................................
4c63ff45
BF
2466
2467Some more interesting work has been done in the upstream project, and
2468"origin" has advanced:
2469
1dc71a91 2470................................................
4c63ff45
BF
2471 o--o--O--o--o--o <-- origin
2472 \
2473 a--b--c <-- mywork
1dc71a91 2474................................................
4c63ff45
BF
2475
2476At this point, you could use "pull" to merge your changes back in;
2477the result would create a new merge commit, like this:
2478
1dc71a91 2479................................................
4c63ff45
BF
2480 o--o--O--o--o--o <-- origin
2481 \ \
2482 a--b--c--m <-- mywork
1dc71a91 2483................................................
a6080a0a 2484
4c63ff45
BF
2485However, if you prefer to keep the history in mywork a simple series of
2486commits without any merges, you may instead choose to use
5162e697 2487linkgit:git-rebase[1]:
4c63ff45
BF
2488
2489-------------------------------------------------
2490$ git checkout mywork
2491$ git rebase origin
2492-------------------------------------------------
2493
b181d57f 2494This will remove each of your commits from mywork, temporarily saving
51ef1daa 2495them as patches (in a directory named ".git/rebase-apply"), update mywork to
b181d57f
BF
2496point at the latest version of origin, then apply each of the saved
2497patches to the new mywork. The result will look like:
4c63ff45
BF
2498
2499
1dc71a91 2500................................................
4c63ff45
BF
2501 o--o--O--o--o--o <-- origin
2502 \
2503 a'--b'--c' <-- mywork
1dc71a91 2504................................................
4c63ff45 2505
b181d57f 2506In the process, it may discover conflicts. In that case it will stop
6127c086 2507and allow you to fix the conflicts; after fixing conflicts, use `git add`
7a7d4ef6 2508to update the index with those contents, and then, instead of
6127c086 2509running `git commit`, just run
4c63ff45
BF
2510
2511-------------------------------------------------
2512$ git rebase --continue
2513-------------------------------------------------
2514
2515and git will continue applying the rest of the patches.
2516
b6cbca38 2517At any point you may use the `--abort` option to abort this process and
4c63ff45
BF
2518return mywork to the state it had before you started the rebase:
2519
2520-------------------------------------------------
2521$ git rebase --abort
2522-------------------------------------------------
2523
7cb192ea
BF
2524[[rewriting-one-commit]]
2525Rewriting a single commit
365aa199
BF
2526-------------------------
2527
7cb192ea 2528We saw in <<fixing-a-mistake-by-rewriting-history>> that you can replace the
365aa199
BF
2529most recent commit using
2530
2531-------------------------------------------------
2532$ git commit --amend
2533-------------------------------------------------
2534
2535which will replace the old commit by a new commit incorporating your
2536changes, giving you a chance to edit the old commit message first.
2537
5162e697 2538You can also use a combination of this and linkgit:git-rebase[1] to
7cb192ea
BF
2539replace a commit further back in your history and recreate the
2540intervening changes on top of it. First, tag the problematic commit
2541with
365aa199
BF
2542
2543-------------------------------------------------
2544$ git tag bad mywork~5
2545-------------------------------------------------
2546
6127c086 2547(Either gitk or `git log` may be useful for finding the commit.)
365aa199 2548
25d9f3fa
BF
2549Then check out that commit, edit it, and rebase the rest of the series
2550on top of it (note that we could check out the commit on a temporary
2551branch, but instead we're using a <<detached-head,detached head>>):
365aa199
BF
2552
2553-------------------------------------------------
25d9f3fa 2554$ git checkout bad
365aa199
BF
2555$ # make changes here and update the index
2556$ git commit --amend
25d9f3fa 2557$ git rebase --onto HEAD bad mywork
365aa199
BF
2558-------------------------------------------------
2559
25d9f3fa
BF
2560When you're done, you'll be left with mywork checked out, with the top
2561patches on mywork reapplied on top of your modified commit. You can
365aa199
BF
2562then clean up with
2563
2564-------------------------------------------------
365aa199
BF
2565$ git tag -d bad
2566-------------------------------------------------
2567
2568Note that the immutable nature of git history means that you haven't really
2569"modified" existing commits; instead, you have replaced the old commits with
2570new commits having new object names.
2571
e34caace 2572[[reordering-patch-series]]
4c63ff45
BF
2573Reordering or selecting from a patch series
2574-------------------------------------------
2575
5162e697 2576Given one existing commit, the linkgit:git-cherry-pick[1] command
b181d57f
BF
2577allows you to apply the change introduced by that commit and create a
2578new commit that records it. So, for example, if "mywork" points to a
2579series of patches on top of "origin", you might do something like:
2580
2581-------------------------------------------------
2582$ git checkout -b mywork-new origin
2583$ gitk origin..mywork &
2584-------------------------------------------------
2585
06ada152 2586and browse through the list of patches in the mywork branch using gitk,
b181d57f 2587applying them (possibly in a different order) to mywork-new using
6127c086 2588cherry-pick, and possibly modifying them as you go using `git commit --amend`.
5162e697 2589The linkgit:git-gui[1] command may also help as it allows you to
6e30fb0c
DK
2590individually select diff hunks for inclusion in the index (by
2591right-clicking on the diff hunk and choosing "Stage Hunk for Commit").
b181d57f 2592
6127c086 2593Another technique is to use `git format-patch` to create a series of
b181d57f 2594patches, then reset the state to before the patches:
4c63ff45 2595
b181d57f
BF
2596-------------------------------------------------
2597$ git format-patch origin
2598$ git reset --hard origin
2599-------------------------------------------------
4c63ff45 2600
b181d57f 2601Then modify, reorder, or eliminate patches as preferred before applying
5162e697 2602them again with linkgit:git-am[1].
4c63ff45 2603
e34caace 2604[[patch-series-tools]]
4c63ff45
BF
2605Other tools
2606-----------
2607
73a1d050 2608There are numerous other tools, such as StGit, which exist for the
79c96c57 2609purpose of maintaining a patch series. These are outside of the scope of
b181d57f 2610this manual.
4c63ff45 2611
aa971cb9 2612[[problems-With-rewriting-history]]
4c63ff45
BF
2613Problems with rewriting history
2614-------------------------------
2615
b181d57f
BF
2616The primary problem with rewriting the history of a branch has to do
2617with merging. Suppose somebody fetches your branch and merges it into
2618their branch, with a result something like this:
2619
1dc71a91 2620................................................
b181d57f
BF
2621 o--o--O--o--o--o <-- origin
2622 \ \
2623 t--t--t--m <-- their branch:
1dc71a91 2624................................................
b181d57f
BF
2625
2626Then suppose you modify the last three commits:
2627
1dc71a91 2628................................................
b181d57f
BF
2629 o--o--o <-- new head of origin
2630 /
2631 o--o--O--o--o--o <-- old head of origin
1dc71a91 2632................................................
b181d57f
BF
2633
2634If we examined all this history together in one repository, it will
2635look like:
2636
1dc71a91 2637................................................
b181d57f
BF
2638 o--o--o <-- new head of origin
2639 /
2640 o--o--O--o--o--o <-- old head of origin
2641 \ \
2642 t--t--t--m <-- their branch:
1dc71a91 2643................................................
b181d57f
BF
2644
2645Git has no way of knowing that the new head is an updated version of
2646the old head; it treats this situation exactly the same as it would if
2647two developers had independently done the work on the old and new heads
2648in parallel. At this point, if someone attempts to merge the new head
2649in to their branch, git will attempt to merge together the two (old and
2650new) lines of development, instead of trying to replace the old by the
2651new. The results are likely to be unexpected.
2652
2653You may still choose to publish branches whose history is rewritten,
2654and it may be useful for others to be able to fetch those branches in
2655order to examine or test them, but they should not attempt to pull such
2656branches into their own work.
2657
2658For true distributed development that supports proper merging,
2659published branches should never be rewritten.
2660
3fb00282
SP
2661[[bisect-merges]]
2662Why bisecting merge commits can be harder than bisecting linear history
2663-----------------------------------------------------------------------
2664
5162e697 2665The linkgit:git-bisect[1] command correctly handles history that
3fb00282
SP
2666includes merge commits. However, when the commit that it finds is a
2667merge commit, the user may need to work harder than usual to figure out
2668why that commit introduced a problem.
2669
2670Imagine this history:
2671
2672................................................
2673 ---Z---o---X---...---o---A---C---D
2674 \ /
2675 o---o---Y---...---o---B
2676................................................
2677
2678Suppose that on the upper line of development, the meaning of one
2679of the functions that exists at Z is changed at commit X. The
2680commits from Z leading to A change both the function's
2681implementation and all calling sites that exist at Z, as well
2682as new calling sites they add, to be consistent. There is no
2683bug at A.
2684
2685Suppose that in the meantime on the lower line of development somebody
2686adds a new calling site for that function at commit Y. The
2687commits from Z leading to B all assume the old semantics of that
2688function and the callers and the callee are consistent with each
2689other. There is no bug at B, either.
2690
2691Suppose further that the two development lines merge cleanly at C,
2692so no conflict resolution is required.
2693
2694Nevertheless, the code at C is broken, because the callers added
2695on the lower line of development have not been converted to the new
2696semantics introduced on the upper line of development. So if all
2697you know is that D is bad, that Z is good, and that
5162e697 2698linkgit:git-bisect[1] identifies C as the culprit, how will you
3fb00282
SP
2699figure out that the problem is due to this change in semantics?
2700
6127c086 2701When the result of a `git bisect` is a non-merge commit, you should
3fb00282
SP
2702normally be able to discover the problem by examining just that commit.
2703Developers can make this easy by breaking their changes into small
2704self-contained commits. That won't help in the case above, however,
2705because the problem isn't obvious from examination of any single
2706commit; instead, a global view of the development is required. To
2707make matters worse, the change in semantics in the problematic
2708function may be just one small part of the changes in the upper
2709line of development.
2710
2711On the other hand, if instead of merging at C you had rebased the
2712history between Z to B on top of A, you would have gotten this
2713linear history:
2714
2715................................................................
2716 ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D*
2717................................................................
2718
2719Bisecting between Z and D* would hit a single culprit commit Y*,
2720and understanding why Y* was broken would probably be easier.
2721
2722Partly for this reason, many experienced git users, even when
2723working on an otherwise merge-heavy project, keep the history
2724linear by rebasing against the latest upstream version before
2725publishing.
2726
e34caace 2727[[advanced-branch-management]]
b181d57f
BF
2728Advanced branch management
2729==========================
4c63ff45 2730
e34caace 2731[[fetching-individual-branches]]
b181d57f
BF
2732Fetching individual branches
2733----------------------------
2734
5162e697 2735Instead of using linkgit:git-remote[1], you can also choose just
b181d57f
BF
2736to update one branch at a time, and to store it locally under an
2737arbitrary name:
2738
2739-------------------------------------------------
2740$ git fetch origin todo:my-todo-work
2741-------------------------------------------------
2742
2743The first argument, "origin", just tells git to fetch from the
2744repository you originally cloned from. The second argument tells git
2745to fetch the branch named "todo" from the remote repository, and to
2746store it locally under the name refs/heads/my-todo-work.
2747
2748You can also fetch branches from other repositories; so
2749
2750-------------------------------------------------
2751$ git fetch git://example.com/proj.git master:example-master
2752-------------------------------------------------
2753
2754will create a new branch named "example-master" and store in it the
2755branch named "master" from the repository at the given URL. If you
2756already have a branch named example-master, it will attempt to
59723040
BF
2757<<fast-forwards,fast-forward>> to the commit given by example.com's
2758master branch. In more detail:
b181d57f 2759
59723040
BF
2760[[fetch-fast-forwards]]
2761git fetch and fast-forwards
2762---------------------------
b181d57f 2763
6127c086 2764In the previous example, when updating an existing branch, "git fetch"
7a7d4ef6 2765checks to make sure that the most recent commit on the remote
b181d57f
BF
2766branch is a descendant of the most recent commit on your copy of the
2767branch before updating your copy of the branch to point at the new
a75d7b54 2768commit. Git calls this process a <<fast-forwards,fast-forward>>.
b181d57f 2769
a75d7b54 2770A fast-forward looks something like this:
b181d57f 2771
1dc71a91 2772................................................
b181d57f
BF
2773 o--o--o--o <-- old head of the branch
2774 \
2775 o--o--o <-- new head of the branch
1dc71a91 2776................................................
b181d57f
BF
2777
2778
2779In some cases it is possible that the new head will *not* actually be
2780a descendant of the old head. For example, the developer may have
2781realized she made a serious mistake, and decided to backtrack,
2782resulting in a situation like:
2783
1dc71a91 2784................................................
b181d57f
BF
2785 o--o--o--o--a--b <-- old head of the branch
2786 \
2787 o--o--o <-- new head of the branch
1dc71a91 2788................................................
b181d57f 2789
6127c086 2790In this case, "git fetch" will fail, and print out a warning.
b181d57f
BF
2791
2792In that case, you can still force git to update to the new head, as
2793described in the following section. However, note that in the
2794situation above this may mean losing the commits labeled "a" and "b",
2795unless you've already created a reference of your own pointing to
2796them.
2797
e34caace 2798[[forcing-fetch]]
6127c086 2799Forcing git fetch to do non-fast-forward updates
b181d57f
BF
2800------------------------------------------------
2801
2802If git fetch fails because the new head of a branch is not a
2803descendant of the old head, you may force the update with:
2804
2805-------------------------------------------------
2806$ git fetch git://example.com/proj.git +master:refs/remotes/example/master
2807-------------------------------------------------
2808
c64415e2
BF
2809Note the addition of the "+" sign. Alternatively, you can use the "-f"
2810flag to force updates of all the fetched branches, as in:
2811
2812-------------------------------------------------
2813$ git fetch -f origin
2814-------------------------------------------------
2815
2816Be aware that commits that the old version of example/master pointed at
2817may be lost, as we saw in the previous section.
b181d57f 2818
e34caace 2819[[remote-branch-configuration]]
29b9a66f
MM
2820Configuring remote-tracking branches
2821------------------------------------
b181d57f
BF
2822
2823We saw above that "origin" is just a shortcut to refer to the
79c96c57 2824repository that you originally cloned from. This information is
b181d57f 2825stored in git configuration variables, which you can see using
5162e697 2826linkgit:git-config[1]:
b181d57f
BF
2827
2828-------------------------------------------------
9d13bda3 2829$ git config -l
b181d57f
BF
2830core.repositoryformatversion=0
2831core.filemode=true
2832core.logallrefupdates=true
2833remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2834remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2835branch.master.remote=origin
2836branch.master.merge=refs/heads/master
2837-------------------------------------------------
2838
2839If there are other repositories that you also use frequently, you can
2840create similar configuration options to save typing; for example,
2841after
2842
2843-------------------------------------------------
9d13bda3 2844$ git config remote.example.url git://example.com/proj.git
b181d57f
BF
2845-------------------------------------------------
2846
2847then the following two commands will do the same thing:
2848
2849-------------------------------------------------
2850$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2851$ git fetch example master:refs/remotes/example/master
2852-------------------------------------------------
2853
2854Even better, if you add one more option:
2855
2856-------------------------------------------------
9d13bda3 2857$ git config remote.example.fetch master:refs/remotes/example/master
b181d57f
BF
2858-------------------------------------------------
2859
2860then the following commands will all do the same thing:
2861
2862-------------------------------------------------
52c80037
BF
2863$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2864$ git fetch example master:refs/remotes/example/master
b181d57f
BF
2865$ git fetch example
2866-------------------------------------------------
2867
2868You can also add a "+" to force the update each time:
2869
2870-------------------------------------------------
9d13bda3 2871$ git config remote.example.fetch +master:ref/remotes/example/master
b181d57f
BF
2872-------------------------------------------------
2873
2874Don't do this unless you're sure you won't mind "git fetch" possibly
4f80b27d 2875throwing away commits on 'example/master'.
b181d57f
BF
2876
2877Also note that all of the above configuration can be performed by
2878directly editing the file .git/config instead of using
5162e697 2879linkgit:git-config[1].
b181d57f 2880
5162e697 2881See linkgit:git-config[1] for more details on the configuration
b181d57f 2882options mentioned above.
d19fbc3c 2883
d19fbc3c 2884
036f8199
BF
2885[[git-concepts]]
2886Git concepts
2887============
d19fbc3c 2888
036f8199
BF
2889Git is built on a small number of simple but powerful ideas. While it
2890is possible to get things done without understanding them, you will find
2891git much more intuitive if you do.
2892
2893We start with the most important, the <<def_object_database,object
2894database>> and the <<def_index,index>>.
b181d57f 2895
e34caace 2896[[the-object-database]]
b181d57f
BF
2897The Object Database
2898-------------------
2899
1bbf1c79
BF
2900
2901We already saw in <<understanding-commits>> that all commits are stored
2902under a 40-digit "object name". In fact, all the information needed to
2903represent the history of a project is stored in objects with such names.
a6e5ef7d
FC
2904In each case the name is calculated by taking the SHA-1 hash of the
2905contents of the object. The SHA-1 hash is a cryptographic hash function.
1bbf1c79
BF
2906What that means to us is that it is impossible to find two different
2907objects with the same name. This has a number of advantages; among
2908others:
2909
2910- Git can quickly determine whether two objects are identical or not,
2911 just by comparing names.
06ada152 2912- Since object names are computed the same way in every repository, the
1bbf1c79
BF
2913 same content stored in two repositories will always be stored under
2914 the same name.
2915- Git can detect errors when it reads an object, by checking that the
a6e5ef7d 2916 object's name is still the SHA-1 hash of its contents.
1bbf1c79
BF
2917
2918(See <<object-details>> for the details of the object formatting and
a6e5ef7d 2919SHA-1 calculation.)
1bbf1c79
BF
2920
2921There are four different types of objects: "blob", "tree", "commit", and
2922"tag".
2923
2924- A <<def_blob_object,"blob" object>> is used to store file data.
843c81dc 2925- A <<def_tree_object,"tree" object>> ties one or more
1bbf1c79
BF
2926 "blob" objects into a directory structure. In addition, a tree object
2927 can refer to other tree objects, thus creating a directory hierarchy.
2928- A <<def_commit_object,"commit" object>> ties such directory hierarchies
2ef8ac1b 2929 together into a <<def_DAG,directed acyclic graph>> of revisions--each
1bbf1c79
BF
2930 commit contains the object name of exactly one tree designating the
2931 directory hierarchy at the time of the commit. In addition, a commit
2932 refers to "parent" commit objects that describe the history of how we
2933 arrived at that directory hierarchy.
2934- A <<def_tag_object,"tag" object>> symbolically identifies and can be
2935 used to sign other objects. It contains the object name and type of
2936 another object, a symbolic name (of course!) and, optionally, a
2937 signature.
b181d57f 2938
b181d57f
BF
2939The object types in some more detail:
2940
513d419c
BF
2941[[commit-object]]
2942Commit Object
2943~~~~~~~~~~~~~
b181d57f 2944
1bbf1c79
BF
2945The "commit" object links a physical state of a tree with a description
2946of how we got there and why. Use the --pretty=raw option to
5162e697 2947linkgit:git-show[1] or linkgit:git-log[1] to examine your favorite
1bbf1c79
BF
2948commit:
2949
2950------------------------------------------------
2951$ git show -s --pretty=raw 2be7fcb476
2952commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4
2953tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf
2954parent 257a84d9d02e90447b149af58b271c19405edb6a
2955author Dave Watson <dwatson@mimvista.com> 1187576872 -0400
2956committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700
2957
2958 Fix misspelling of 'suppress' in docs
2959
2960 Signed-off-by: Junio C Hamano <gitster@pobox.com>
2961------------------------------------------------
2962
2963As you can see, a commit is defined by:
2964
a6e5ef7d 2965- a tree: The SHA-1 name of a tree object (as defined below), representing
1bbf1c79 2966 the contents of a directory at a certain point in time.
a6e5ef7d 2967- parent(s): The SHA-1 name of some number of commits which represent the
9e5d87d4 2968 immediately previous step(s) in the history of the project. The
1bbf1c79
BF
2969 example above has one parent; merge commits may have more than
2970 one. A commit with no parents is called a "root" commit, and
2971 represents the initial revision of a project. Each project must have
2972 at least one root. A project can also have multiple roots, though
2973 that isn't common (or necessarily a good idea).
2974- an author: The name of the person responsible for this change, together
2975 with its date.
2976- a committer: The name of the person who actually created the commit,
2977 with the date it was done. This may be different from the author, for
2978 example, if the author was someone who wrote a patch and emailed it
2979 to the person who used it to create the commit.
2980- a comment describing this commit.
2981
2982Note that a commit does not itself contain any information about what
2983actually changed; all changes are calculated by comparing the contents
2984of the tree referred to by this commit with the trees associated with
2985its parents. In particular, git does not attempt to record file renames
2986explicitly, though it can identify cases where the existence of the same
2987file data at changing paths suggests a rename. (See, for example, the
5162e697 2988-M option to linkgit:git-diff[1]).
1bbf1c79 2989
5162e697 2990A commit is usually created by linkgit:git-commit[1], which creates a
1bbf1c79
BF
2991commit whose parent is normally the current HEAD, and whose tree is
2992taken from the content currently stored in the index.
b181d57f 2993
e34caace 2994[[tree-object]]
b181d57f 2995Tree Object
971aa71f 2996~~~~~~~~~~~
b181d57f 2997
5162e697
DM
2998The ever-versatile linkgit:git-show[1] command can also be used to
2999examine tree objects, but linkgit:git-ls-tree[1] will give you more
1bbf1c79
BF
3000details:
3001
3002------------------------------------------------
3003$ git ls-tree fb3a8bdd0ce
3004100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore
3005100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap
3006100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING
3007040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation
3008100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN
3009100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL
3010100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile
3011100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README
3012...
3013------------------------------------------------
3014
3015As you can see, a tree object contains a list of entries, each with a
a6e5ef7d 3016mode, object type, SHA-1 name, and name, sorted by name. It represents
1bbf1c79
BF
3017the contents of a single directory tree.
3018
3019The object type may be a blob, representing the contents of a file, or
3020another tree, representing the contents of a subdirectory. Since trees
a6e5ef7d
FC
3021and blobs, like all other objects, are named by the SHA-1 hash of their
3022contents, two trees have the same SHA-1 name if and only if their
1bbf1c79
BF
3023contents (including, recursively, the contents of all subdirectories)
3024are identical. This allows git to quickly determine the differences
3025between two related tree objects, since it can ignore any entries with
3026identical object names.
3027
3028(Note: in the presence of submodules, trees may also have commits as
6dd14366 3029entries. See <<submodules>> for documentation.)
1bbf1c79
BF
3030
3031Note that the files all have mode 644 or 755: git actually only pays
3032attention to the executable bit.
b181d57f 3033
513d419c
BF
3034[[blob-object]]
3035Blob Object
3036~~~~~~~~~~~
b181d57f 3037
5162e697 3038You can use linkgit:git-show[1] to examine the contents of a blob; take,
1bbf1c79 3039for example, the blob in the entry for "COPYING" from the tree above:
b181d57f 3040
1bbf1c79
BF
3041------------------------------------------------
3042$ git show 6ff87c4664
3043
3044 Note that the only valid version of the GPL as far as this project
3045 is concerned is _this_ particular version of the license (ie v2, not
3046 v2.2 or v3.x or whatever), unless explicitly otherwise stated.
3047...
3048------------------------------------------------
b181d57f 3049
1bbf1c79
BF
3050A "blob" object is nothing but a binary blob of data. It doesn't refer
3051to anything else or have attributes of any kind.
3052
3053Since the blob is entirely defined by its data, if two files in a
3054directory tree (or in multiple different versions of the repository)
3055have the same contents, they will share the same blob object. The object
3056is totally independent of its location in the directory tree, and
3057renaming a file does not change the object that file is associated with.
3058
3059Note that any tree or blob object can be examined using
5162e697 3060linkgit:git-show[1] with the <revision>:<path> syntax. This can
1bbf1c79
BF
3061sometimes be useful for browsing the contents of a tree that is not
3062currently checked out.
b181d57f 3063
e34caace 3064[[trust]]
b181d57f 3065Trust
971aa71f 3066~~~~~
b181d57f 3067
a6e5ef7d 3068If you receive the SHA-1 name of a blob from one source, and its contents
1bbf1c79 3069from another (possibly untrusted) source, you can still trust that those
a6e5ef7d
FC
3070contents are correct as long as the SHA-1 name agrees. This is because
3071the SHA-1 is designed so that it is infeasible to find different contents
1bbf1c79 3072that produce the same hash.
b181d57f 3073
a6e5ef7d 3074Similarly, you need only trust the SHA-1 name of a top-level tree object
1bbf1c79 3075to trust the contents of the entire directory that it refers to, and if
a6e5ef7d 3076you receive the SHA-1 name of a commit from a trusted source, then you
1bbf1c79
BF
3077can easily verify the entire history of commits reachable through
3078parents of that commit, and all of those contents of the trees referred
3079to by those commits.
b181d57f
BF
3080
3081So to introduce some real trust in the system, the only thing you need
3082to do is to digitally sign just 'one' special note, which includes the
3083name of a top-level commit. Your digital signature shows others
3084that you trust that commit, and the immutability of the history of
3085commits tells others that they can trust the whole history.
3086
3087In other words, you can easily validate a whole archive by just
a6e5ef7d 3088sending out a single email that tells the people the name (SHA-1 hash)
b181d57f
BF
3089of the top commit, and digitally sign that email using something
3090like GPG/PGP.
3091
3092To assist in this, git also provides the tag object...
3093
e34caace 3094[[tag-object]]
b181d57f 3095Tag Object
971aa71f 3096~~~~~~~~~~
b181d57f 3097
1bbf1c79
BF
3098A tag object contains an object, object type, tag name, the name of the
3099person ("tagger") who created the tag, and a message, which may contain
843c81dc 3100a signature, as can be seen using linkgit:git-cat-file[1]:
b181d57f 3101
1bbf1c79
BF
3102------------------------------------------------
3103$ git cat-file tag v1.5.0
3104object 437b1b20df4b356c9342dac8d38849f24ef44f27
3105type commit
3106tag v1.5.0
3107tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000
3108
3109GIT 1.5.0
3110-----BEGIN PGP SIGNATURE-----
3111Version: GnuPG v1.4.6 (GNU/Linux)
3112
3113iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui
3114nLE/L9aUXdWeTFPron96DLA=
3115=2E+0
3116-----END PGP SIGNATURE-----
3117------------------------------------------------
b181d57f 3118
5162e697
DM
3119See the linkgit:git-tag[1] command to learn how to create and verify tag
3120objects. (Note that linkgit:git-tag[1] can also be used to create
1bbf1c79 3121"lightweight tags", which are not tag objects at all, but just simple
fc74ecc1 3122references whose names begin with "refs/tags/").
b181d57f 3123
09eff7b0
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3124[[pack-files]]
3125How git stores objects efficiently: pack files
3126~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3127
9644ffdd 3128Newly created objects are initially created in a file named after the
a6e5ef7d 3129object's SHA-1 hash (stored in .git/objects).
09eff7b0
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3130
3131Unfortunately this system becomes inefficient once a project has a
3132lot of objects. Try this on an old project:
3133
3134------------------------------------------------
3135$ git count-objects
31366930 objects, 47620 kilobytes
3137------------------------------------------------
3138
3139The first number is the number of objects which are kept in
3140individual files. The second is the amount of space taken up by
3141those "loose" objects.
3142
3143You can save space and make git faster by moving these loose objects in
3144to a "pack file", which stores a group of objects in an efficient
3145compressed format; the details of how pack files are formatted can be
3146found in link:technical/pack-format.txt[technical/pack-format.txt].
3147
3148To put the loose objects into a pack, just run git repack:
3149
3150------------------------------------------------
3151$ git repack
3152Generating pack...
3153Done counting 6020 objects.
3154Deltifying 6020 objects.
3155 100% (6020/6020) done
3156Writing 6020 objects.
3157 100% (6020/6020) done
3158Total 6020, written 6020 (delta 4070), reused 0 (delta 0)
3159Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.
3160------------------------------------------------
3161
3162You can then run
3163
3164------------------------------------------------
3165$ git prune
3166------------------------------------------------
3167
3168to remove any of the "loose" objects that are now contained in the
3169pack. This will also remove any unreferenced objects (which may be
6127c086 3170created when, for example, you use "git reset" to remove a commit).
09eff7b0
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3171You can verify that the loose objects are gone by looking at the
3172.git/objects directory or by running
3173
3174------------------------------------------------
3175$ git count-objects
31760 objects, 0 kilobytes
3177------------------------------------------------
3178
3179Although the object files are gone, any commands that refer to those
3180objects will work exactly as they did before.
3181
5162e697 3182The linkgit:git-gc[1] command performs packing, pruning, and more for
09eff7b0
BF
3183you, so is normally the only high-level command you need.
3184
3185[[dangling-objects]]
3186Dangling objects
3187~~~~~~~~~~~~~~~~
3188
5162e697 3189The linkgit:git-fsck[1] command will sometimes complain about dangling
09eff7b0
BF
3190objects. They are not a problem.
3191
3192The most common cause of dangling objects is that you've rebased a
3193branch, or you have pulled from somebody else who rebased a branch--see
3194<<cleaning-up-history>>. In that case, the old head of the original
3195branch still exists, as does everything it pointed to. The branch
3196pointer itself just doesn't, since you replaced it with another one.
3197
3198There are also other situations that cause dangling objects. For
6127c086 3199example, a "dangling blob" may arise because you did a "git add" of a
09eff7b0
BF
3200file, but then, before you actually committed it and made it part of the
3201bigger picture, you changed something else in that file and committed
2ef8ac1b 3202that *updated* thing--the old state that you added originally ends up
09eff7b0
BF
3203not being pointed to by any commit or tree, so it's now a dangling blob
3204object.
3205
3206Similarly, when the "recursive" merge strategy runs, and finds that
3207there are criss-cross merges and thus more than one merge base (which is
3208fairly unusual, but it does happen), it will generate one temporary
3209midway tree (or possibly even more, if you had lots of criss-crossing
3210merges and more than two merge bases) as a temporary internal merge
3211base, and again, those are real objects, but the end result will not end
3212up pointing to them, so they end up "dangling" in your repository.
3213
3214Generally, dangling objects aren't anything to worry about. They can
3215even be very useful: if you screw something up, the dangling objects can
3216be how you recover your old tree (say, you did a rebase, and realized
2ef8ac1b 3217that you really didn't want to--you can look at what dangling objects
09eff7b0
BF
3218you have, and decide to reset your head to some old dangling state).
3219
3220For commits, you can just use:
3221
3222------------------------------------------------
3223$ gitk <dangling-commit-sha-goes-here> --not --all
3224------------------------------------------------
3225
3226This asks for all the history reachable from the given commit but not
3227from any branch, tag, or other reference. If you decide it's something
3228you want, you can always create a new reference to it, e.g.,
3229
3230------------------------------------------------
3231$ git branch recovered-branch <dangling-commit-sha-goes-here>
3232------------------------------------------------
3233
3234For blobs and trees, you can't do the same, but you can still examine
3235them. You can just do
3236
3237------------------------------------------------
3238$ git show <dangling-blob/tree-sha-goes-here>
3239------------------------------------------------
3240
3241to show what the contents of the blob were (or, for a tree, basically
3242what the "ls" for that directory was), and that may give you some idea
3243of what the operation was that left that dangling object.
3244
3245Usually, dangling blobs and trees aren't very interesting. They're
3246almost always the result of either being a half-way mergebase (the blob
3247will often even have the conflict markers from a merge in it, if you
3248have had conflicting merges that you fixed up by hand), or simply
6127c086 3249because you interrupted a "git fetch" with ^C or something like that,
09eff7b0
BF
3250leaving _some_ of the new objects in the object database, but just
3251dangling and useless.
3252
3253Anyway, once you are sure that you're not interested in any dangling
3254state, you can just prune all unreachable objects:
3255
3256------------------------------------------------
3257$ git prune
3258------------------------------------------------
3259
3260and they'll be gone. But you should only run "git prune" on a quiescent
2ef8ac1b 3261repository--it's kind of like doing a filesystem fsck recovery: you
09eff7b0
BF
3262don't want to do that while the filesystem is mounted.
3263
6127c086
FC
3264(The same is true of "git fsck" itself, btw, but since
3265`git fsck` never actually *changes* the repository, it just reports
3266on what it found, `git fsck` itself is never 'dangerous' to run.
09eff7b0
BF
3267Running it while somebody is actually changing the repository can cause
3268confusing and scary messages, but it won't actually do anything bad. In
3269contrast, running "git prune" while somebody is actively changing the
3270repository is a *BAD* idea).
b181d57f 3271
1cdade2c
BF
3272[[recovering-from-repository-corruption]]
3273Recovering from repository corruption
3274~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3275
3276By design, git treats data trusted to it with caution. However, even in
3277the absence of bugs in git itself, it is still possible that hardware or
3278operating system errors could corrupt data.
3279
3280The first defense against such problems is backups. You can back up a
3281git directory using clone, or just using cp, tar, or any other backup
3282mechanism.
3283
3284As a last resort, you can search for the corrupted objects and attempt
3285to replace them by hand. Back up your repository before attempting this
3286in case you corrupt things even more in the process.
3287
3288We'll assume that the problem is a single missing or corrupted blob,
9e5d87d4 3289which is sometimes a solvable problem. (Recovering missing trees and
1cdade2c
BF
3290especially commits is *much* harder).
3291
3292Before starting, verify that there is corruption, and figure out where
5162e697 3293it is with linkgit:git-fsck[1]; this may be time-consuming.
1cdade2c
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3294