user-manual: Update for receive.denyCurrentBranch=refuse
[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______________________________________________
d19fbc3c 3
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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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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
d55ae921
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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
b181d57f
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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
629d9f78
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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
BF
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
d19fbc3c
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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
BF
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
52ffe995
JW
1139description. The text up to the first blank line in a commit
1140message is treated as the commit title, and that title is used
1141throughout git. For example, linkgit:git-format-patch[1] turns a
1142commit into email, and it uses the title on the Subject line and the
1143rest of the commit in the body.
1144
d19fbc3c 1145
2dc53617
JH
1146[[ignoring-files]]
1147Ignoring files
1148--------------
1149
1150A project will often generate files that you do 'not' want to track with git.
1151This typically includes files generated by a build process or temporary
1152backup files made by your editor. Of course, 'not' tracking files with git
6127c086 1153is just a matter of 'not' calling `git add` on them. But it quickly becomes
2dc53617 1154annoying to have these untracked files lying around; e.g. they make
dcb11263
CJ
1155`git add .` practically useless, and they keep showing up in the output of
1156`git status`.
2dc53617 1157
464a8a7a
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1158You can tell git to ignore certain files by creating a file called .gitignore
1159in the top level of your working directory, with contents such as:
2dc53617
JH
1160
1161-------------------------------------------------
1162# Lines starting with '#' are considered comments.
464a8a7a 1163# Ignore any file named foo.txt.
2dc53617
JH
1164foo.txt
1165# Ignore (generated) html files,
1166*.html
1167# except foo.html which is maintained by hand.
1168!foo.html
1169# Ignore objects and archives.
1170*.[oa]
1171-------------------------------------------------
1172
5162e697 1173See linkgit:gitignore[5] for a detailed explanation of the syntax. You can
464a8a7a
BF
1174also place .gitignore files in other directories in your working tree, and they
1175will apply to those directories and their subdirectories. The `.gitignore`
1176files can be added to your repository like any other files (just run `git add
1177.gitignore` and `git commit`, as usual), which is convenient when the exclude
1178patterns (such as patterns matching build output files) would also make sense
1179for other users who clone your repository.
1180
1181If you wish the exclude patterns to affect only certain repositories
1182(instead of every repository for a given project), you may instead put
1183them in a file in your repository named .git/info/exclude, or in any file
1184specified by the `core.excludesfile` configuration variable. Some git
1185commands can also take exclude patterns directly on the command line.
5162e697 1186See linkgit:gitignore[5] for the details.
2dc53617 1187
e34caace 1188[[how-to-merge]]
ae25c67a 1189How to merge
d19fbc3c
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1190------------
1191
1192You can rejoin two diverging branches of development using
5162e697 1193linkgit:git-merge[1]:
d19fbc3c
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1194
1195-------------------------------------------------
1196$ git merge branchname
1197-------------------------------------------------
1198
1199merges the development in the branch "branchname" into the current
e63ec003
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1200branch.
1201
1202A merge is made by combining the changes made in "branchname" and the
1203changes made up to the latest commit in your current branch since
1204their histories forked. The work tree is overwritten by the result of
1205the merge when this combining is done cleanly, or overwritten by a
1206half-merged results when this combining results in conflicts.
1207Therefore, if you have uncommitted changes touching the same files as
1208the ones impacted by the merge, Git will refuse to proceed. Most of
1209the time, you will want to commit your changes before you can merge,
1210and if you don't, then linkgit:git-stash[1] can take these changes
1211away while you're doing the merge, and reapply them afterwards.
1212
6a5d0b0a 1213If the changes are independent enough, Git will automatically complete
e63ec003
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1214the merge and commit the result (or reuse an existing commit in case
1215of <<fast-forwards,fast-forward>>, see below). On the other hand,
1216if there are conflicts--for example, if the same file is
d19fbc3c
BF
1217modified in two different ways in the remote branch and the local
1218branch--then you are warned; the output may look something like this:
1219
1220-------------------------------------------------
fabbd8f6
BF
1221$ git merge next
1222 100% (4/4) done
1223Auto-merged file.txt
d19fbc3c
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1224CONFLICT (content): Merge conflict in file.txt
1225Automatic merge failed; fix conflicts and then commit the result.
1226-------------------------------------------------
1227
1228Conflict markers are left in the problematic files, and after
1229you resolve the conflicts manually, you can update the index
1230with the contents and run git commit, as you normally would when
1231creating a new file.
1232
1233If you examine the resulting commit using gitk, you will see that it
1234has two parents, one pointing to the top of the current branch, and
1235one to the top of the other branch.
1236
d19fbc3c
BF
1237[[resolving-a-merge]]
1238Resolving a merge
1239-----------------
1240
1241When a merge isn't resolved automatically, git leaves the index and
1242the working tree in a special state that gives you all the
1243information you need to help resolve the merge.
1244
1245Files with conflicts are marked specially in the index, so until you
5162e697 1246resolve the problem and update the index, linkgit:git-commit[1] will
ef561ac7 1247fail:
d19fbc3c
BF
1248
1249-------------------------------------------------
1250$ git commit
1251file.txt: needs merge
1252-------------------------------------------------
1253
5162e697 1254Also, linkgit:git-status[1] will list those files as "unmerged", and the
ef561ac7
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1255files with conflicts will have conflict markers added, like this:
1256
1257-------------------------------------------------
1258<<<<<<< HEAD:file.txt
1259Hello world
1260=======
1261Goodbye
1262>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1263-------------------------------------------------
1264
1265All you need to do is edit the files to resolve the conflicts, and then
1266
1267-------------------------------------------------
1268$ git add file.txt
1269$ git commit
1270-------------------------------------------------
1271
1272Note that the commit message will already be filled in for you with
1273some information about the merge. Normally you can just use this
1274default message unchanged, but you may add additional commentary of
1275your own if desired.
1276
1277The above is all you need to know to resolve a simple merge. But git
1278also provides more information to help resolve conflicts:
1279
e34caace 1280[[conflict-resolution]]
ef561ac7
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1281Getting conflict-resolution help during a merge
1282~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
1283
1284All of the changes that git was able to merge automatically are
5162e697 1285already added to the index file, so linkgit:git-diff[1] shows only
ef561ac7 1286the conflicts. It uses an unusual syntax:
d19fbc3c
BF
1287
1288-------------------------------------------------
1289$ git diff
1290diff --cc file.txt
1291index 802992c,2b60207..0000000
1292--- a/file.txt
1293+++ b/file.txt
1294@@@ -1,1 -1,1 +1,5 @@@
1295++<<<<<<< HEAD:file.txt
1296 +Hello world
1297++=======
1298+ Goodbye
1299++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1300-------------------------------------------------
1301
1130845b 1302Recall that the commit which will be committed after we resolve this
d19fbc3c
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1303conflict will have two parents instead of the usual one: one parent
1304will be HEAD, the tip of the current branch; the other will be the
1305tip of the other branch, which is stored temporarily in MERGE_HEAD.
1306
ef561ac7
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1307During the merge, the index holds three versions of each file. Each of
1308these three "file stages" represents a different version of the file:
1309
1310-------------------------------------------------
1311$ git show :1:file.txt # the file in a common ancestor of both branches
4209752d
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1312$ git show :2:file.txt # the version from HEAD.
1313$ git show :3:file.txt # the version from MERGE_HEAD.
ef561ac7
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1314-------------------------------------------------
1315
4209752d
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1316When you ask linkgit:git-diff[1] to show the conflicts, it runs a
1317three-way diff between the conflicted merge results in the work tree with
1318stages 2 and 3 to show only hunks whose contents come from both sides,
1319mixed (in other words, when a hunk's merge results come only from stage 2,
1320that part is not conflicting and is not shown. Same for stage 3).
ef561ac7
BF
1321
1322The diff above shows the differences between the working-tree version of
1323file.txt and the stage 2 and stage 3 versions. So instead of preceding
1324each line by a single "+" or "-", it now uses two columns: the first
1325column is used for differences between the first parent and the working
1326directory copy, and the second for differences between the second parent
1327and the working directory copy. (See the "COMBINED DIFF FORMAT" section
5162e697 1328of linkgit:git-diff-files[1] for a details of the format.)
ef561ac7
BF
1329
1330After resolving the conflict in the obvious way (but before updating the
1331index), the diff will look like:
d19fbc3c
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1332
1333-------------------------------------------------
1334$ git diff
1335diff --cc file.txt
1336index 802992c,2b60207..0000000
1337--- a/file.txt
1338+++ b/file.txt
1339@@@ -1,1 -1,1 +1,1 @@@
1340- Hello world
1341 -Goodbye
1342++Goodbye world
1343-------------------------------------------------
1344
1345This shows that our resolved version deleted "Hello world" from the
1346first parent, deleted "Goodbye" from the second parent, and added
1347"Goodbye world", which was previously absent from both.
1348
ef561ac7
BF
1349Some special diff options allow diffing the working directory against
1350any of these stages:
1351
1352-------------------------------------------------
1353$ git diff -1 file.txt # diff against stage 1
1354$ git diff --base file.txt # same as the above
1355$ git diff -2 file.txt # diff against stage 2
1356$ git diff --ours file.txt # same as the above
1357$ git diff -3 file.txt # diff against stage 3
1358$ git diff --theirs file.txt # same as the above.
1359-------------------------------------------------
1360
0cafe944 1361The linkgit:git-log[1] and linkgit:gitk[1] commands also provide special help
ef561ac7 1362for merges:
d19fbc3c
BF
1363
1364-------------------------------------------------
1365$ git log --merge
ef561ac7 1366$ gitk --merge
d19fbc3c
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1367-------------------------------------------------
1368
ef561ac7
BF
1369These will display all commits which exist only on HEAD or on
1370MERGE_HEAD, and which touch an unmerged file.
d19fbc3c 1371
5162e697 1372You may also use linkgit:git-mergetool[1], which lets you merge the
c7719fbe 1373unmerged files using external tools such as Emacs or kdiff3.
c64415e2 1374
ef561ac7 1375Each time you resolve the conflicts in a file and update the index:
d19fbc3c
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1376
1377-------------------------------------------------
1378$ git add file.txt
d19fbc3c
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1379-------------------------------------------------
1380
ef561ac7 1381the different stages of that file will be "collapsed", after which
6127c086 1382`git diff` will (by default) no longer show diffs for that file.
d19fbc3c
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1383
1384[[undoing-a-merge]]
ae25c67a 1385Undoing a merge
d19fbc3c
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1386---------------
1387
1388If you get stuck and decide to just give up and throw the whole mess
1389away, you can always return to the pre-merge state with
1390
1391-------------------------------------------------
1392$ git reset --hard HEAD
1393-------------------------------------------------
1394
1130845b 1395Or, if you've already committed the merge that you want to throw away,
d19fbc3c
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1396
1397-------------------------------------------------
1c73bb0e 1398$ git reset --hard ORIG_HEAD
d19fbc3c
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1399-------------------------------------------------
1400
1401However, this last command can be dangerous in some cases--never
1402throw away a commit you have already committed if that commit may
1403itself have been merged into another branch, as doing so may confuse
1404further merges.
1405
e34caace 1406[[fast-forwards]]
d19fbc3c
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1407Fast-forward merges
1408-------------------
1409
1410There is one special case not mentioned above, which is treated
1411differently. Normally, a merge results in a merge commit, with two
1412parents, one pointing at each of the two lines of development that
1413were merged.
1414
59723040
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1415However, if the current branch is a descendant of the other--so every
1416commit present in the one is already contained in the other--then git
a75d7b54 1417just performs a "fast-forward"; the head of the current branch is moved
59723040
BF
1418forward to point at the head of the merged-in branch, without any new
1419commits being created.
d19fbc3c 1420
e34caace 1421[[fixing-mistakes]]
b684f830
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1422Fixing mistakes
1423---------------
1424
1425If you've messed up the working tree, but haven't yet committed your
1426mistake, you can return the entire working tree to the last committed
1427state with
1428
1429-------------------------------------------------
1430$ git reset --hard HEAD
1431-------------------------------------------------
1432
1433If you make a commit that you later wish you hadn't, there are two
1434fundamentally different ways to fix the problem:
1435
1436 1. You can create a new commit that undoes whatever was done
93cbbd71 1437 by the old commit. This is the correct thing if your
b684f830
BF
1438 mistake has already been made public.
1439
1440 2. You can go back and modify the old commit. You should
1441 never do this if you have already made the history public;
1442 git does not normally expect the "history" of a project to
1443 change, and cannot correctly perform repeated merges from
1444 a branch that has had its history changed.
1445
e34caace 1446[[reverting-a-commit]]
b684f830
BF
1447Fixing a mistake with a new commit
1448~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1449
1450Creating a new commit that reverts an earlier change is very easy;
5162e697 1451just pass the linkgit:git-revert[1] command a reference to the bad
b684f830
BF
1452commit; for example, to revert the most recent commit:
1453
1454-------------------------------------------------
1455$ git revert HEAD
1456-------------------------------------------------
1457
1458This will create a new commit which undoes the change in HEAD. You
1459will be given a chance to edit the commit message for the new commit.
1460
1461You can also revert an earlier change, for example, the next-to-last:
1462
1463-------------------------------------------------
1464$ git revert HEAD^
1465-------------------------------------------------
1466
1467In this case git will attempt to undo the old change while leaving
1468intact any changes made since then. If more recent changes overlap
1469with the changes to be reverted, then you will be asked to fix
1470conflicts manually, just as in the case of <<resolving-a-merge,
1471resolving a merge>>.
1472
7cb192ea
BF
1473[[fixing-a-mistake-by-rewriting-history]]
1474Fixing a mistake by rewriting history
b684f830
BF
1475~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1476
1477If the problematic commit is the most recent commit, and you have not
1478yet made that commit public, then you may just
6127c086 1479<<undoing-a-merge,destroy it using `git reset`>>.
b684f830
BF
1480
1481Alternatively, you
1482can edit the working directory and update the index to fix your
1483mistake, just as if you were going to <<how-to-make-a-commit,create a
1484new commit>>, then run
1485
1486-------------------------------------------------
1487$ git commit --amend
1488-------------------------------------------------
1489
1490which will replace the old commit by a new commit incorporating your
1491changes, giving you a chance to edit the old commit message first.
1492
1493Again, you should never do this to a commit that may already have
5162e697 1494been merged into another branch; use linkgit:git-revert[1] instead in
b684f830
BF
1495that case.
1496
7cb192ea 1497It is also possible to replace commits further back in the history, but
b684f830
BF
1498this is an advanced topic to be left for
1499<<cleaning-up-history,another chapter>>.
1500
e34caace 1501[[checkout-of-path]]
b684f830
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1502Checking out an old version of a file
1503~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1504
1505In the process of undoing a previous bad change, you may find it
1506useful to check out an older version of a particular file using
6127c086 1507linkgit:git-checkout[1]. We've used `git checkout` before to switch
b684f830
BF
1508branches, but it has quite different behavior if it is given a path
1509name: the command
1510
1511-------------------------------------------------
1512$ git checkout HEAD^ path/to/file
1513-------------------------------------------------
1514
1515replaces path/to/file by the contents it had in the commit HEAD^, and
1516also updates the index to match. It does not change branches.
1517
1518If you just want to look at an old version of the file, without
1519modifying the working directory, you can do that with
5162e697 1520linkgit:git-show[1]:
b684f830
BF
1521
1522-------------------------------------------------
ed4eb0d8 1523$ git show HEAD^:path/to/file
b684f830
BF
1524-------------------------------------------------
1525
1526which will display the given version of the file.
1527
7a7cc594
JH
1528[[interrupted-work]]
1529Temporarily setting aside work in progress
1530~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1531
1532While you are in the middle of working on something complicated, you
1533find an unrelated but obvious and trivial bug. You would like to fix it
5162e697 1534before continuing. You can use linkgit:git-stash[1] to save the current
7a7cc594
JH
1535state of your work, and after fixing the bug (or, optionally after doing
1536so on a different branch and then coming back), unstash the
1537work-in-progress changes.
1538
1539------------------------------------------------
7a85f6ae 1540$ git stash save "work in progress for foo feature"
7a7cc594
JH
1541------------------------------------------------
1542
1543This command will save your changes away to the `stash`, and
1544reset your working tree and the index to match the tip of your
1545current branch. Then you can make your fix as usual.
1546
1547------------------------------------------------
1548... edit and test ...
1549$ git commit -a -m "blorpl: typofix"
1550------------------------------------------------
1551
1552After that, you can go back to what you were working on with
7b8988e1 1553`git stash pop`:
7a7cc594
JH
1554
1555------------------------------------------------
7b8988e1 1556$ git stash pop
7a7cc594
JH
1557------------------------------------------------
1558
1559
e34caace 1560[[ensuring-good-performance]]
d19fbc3c
BF
1561Ensuring good performance
1562-------------------------
1563
1564On large repositories, git depends on compression to keep the history
06ada152 1565information from taking up too much space on disk or in memory.
d19fbc3c
BF
1566
1567This compression is not performed automatically. Therefore you
5162e697 1568should occasionally run linkgit:git-gc[1]:
d19fbc3c
BF
1569
1570-------------------------------------------------
1571$ git gc
1572-------------------------------------------------
1573
17217090 1574to recompress the archive. This can be very time-consuming, so
6127c086 1575you may prefer to run `git gc` when you are not doing other work.
d19fbc3c 1576
e34caace
BF
1577
1578[[ensuring-reliability]]
11e016a3
BF
1579Ensuring reliability
1580--------------------
1581
e34caace 1582[[checking-for-corruption]]
11e016a3
BF
1583Checking the repository for corruption
1584~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1585
5162e697 1586The linkgit:git-fsck[1] command runs a number of self-consistency checks
1191ee18 1587on the repository, and reports on any problems. This may take some
c6a13b2c 1588time.
21dcb3b7
BF
1589
1590-------------------------------------------------
04e50e94 1591$ git fsck
21dcb3b7
BF
1592dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1593dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1594dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1595dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1596dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1597dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1598dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1599dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1600...
1601-------------------------------------------------
1602
c6a13b2c
JH
1603You will see informational messages on dangling objects. They are objects
1604that still exist in the repository but are no longer referenced by any of
1605your branches, and can (and will) be removed after a while with "gc".
b4ab1980 1606You can run `git fsck --no-dangling` to suppress these messages, and still
c6a13b2c 1607view real errors.
1cdade2c 1608
e34caace 1609[[recovering-lost-changes]]
11e016a3
BF
1610Recovering lost changes
1611~~~~~~~~~~~~~~~~~~~~~~~
1612
e34caace 1613[[reflogs]]
559e4d7a
BF
1614Reflogs
1615^^^^^^^
1616
6cf378f0 1617Say you modify a branch with +linkgit:git-reset[1] \--hard+, and then
559e4d7a
BF
1618realize that the branch was the only reference you had to that point in
1619history.
1620
1621Fortunately, git also keeps a log, called a "reflog", of all the
1622previous values of each branch. So in this case you can still find the
a6080a0a 1623old history using, for example,
559e4d7a
BF
1624
1625-------------------------------------------------
1626$ git log master@{1}
1627-------------------------------------------------
1628
e502c2c3
SO
1629This lists the commits reachable from the previous version of the
1630"master" branch head. This syntax can be used with any git command
1631that accepts a commit, not just with git log. Some other examples:
559e4d7a
BF
1632
1633-------------------------------------------------
1634$ git show master@{2} # See where the branch pointed 2,
1635$ git show master@{3} # 3, ... changes ago.
1636$ gitk master@{yesterday} # See where it pointed yesterday,
1637$ gitk master@{"1 week ago"} # ... or last week
953f3d6f
BF
1638$ git log --walk-reflogs master # show reflog entries for master
1639-------------------------------------------------
1640
1641A separate reflog is kept for the HEAD, so
1642
1643-------------------------------------------------
1644$ git show HEAD@{"1 week ago"}
559e4d7a
BF
1645-------------------------------------------------
1646
953f3d6f
BF
1647will show what HEAD pointed to one week ago, not what the current branch
1648pointed to one week ago. This allows you to see the history of what
1649you've checked out.
1650
559e4d7a 1651The reflogs are kept by default for 30 days, after which they may be
5162e697 1652pruned. See linkgit:git-reflog[1] and linkgit:git-gc[1] to learn
559e4d7a 1653how to control this pruning, and see the "SPECIFYING REVISIONS"
9d83e382 1654section of linkgit:gitrevisions[7] for details.
559e4d7a
BF
1655
1656Note that the reflog history is very different from normal git history.
1657While normal history is shared by every repository that works on the
1658same project, the reflog history is not shared: it tells you only about
1659how the branches in your local repository have changed over time.
1660
59723040 1661[[dangling-object-recovery]]
559e4d7a
BF
1662Examining dangling objects
1663^^^^^^^^^^^^^^^^^^^^^^^^^^
1664
59723040
BF
1665In some situations the reflog may not be able to save you. For example,
1666suppose you delete a branch, then realize you need the history it
1667contained. The reflog is also deleted; however, if you have not yet
1668pruned the repository, then you may still be able to find the lost
6127c086 1669commits in the dangling objects that `git fsck` reports. See
59723040 1670<<dangling-objects>> for the details.
559e4d7a
BF
1671
1672-------------------------------------------------
1673$ git fsck
1674dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1675dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1676dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1677...
1678-------------------------------------------------
1679
aacd404e 1680You can examine
559e4d7a
BF
1681one of those dangling commits with, for example,
1682
1683------------------------------------------------
1684$ gitk 7281251ddd --not --all
1685------------------------------------------------
1686
1687which does what it sounds like: it says that you want to see the commit
1688history that is described by the dangling commit(s), but not the
1689history that is described by all your existing branches and tags. Thus
1690you get exactly the history reachable from that commit that is lost.
1691(And notice that it might not be just one commit: we only report the
1692"tip of the line" as being dangling, but there might be a whole deep
79c96c57 1693and complex commit history that was dropped.)
559e4d7a
BF
1694
1695If you decide you want the history back, you can always create a new
1696reference pointing to it, for example, a new branch:
1697
1698------------------------------------------------
a6080a0a 1699$ git branch recovered-branch 7281251ddd
559e4d7a
BF
1700------------------------------------------------
1701
59723040
BF
1702Other types of dangling objects (blobs and trees) are also possible, and
1703dangling objects can arise in other situations.
1704
11e016a3 1705
e34caace 1706[[sharing-development]]
d19fbc3c 1707Sharing development with others
b684f830 1708===============================
d19fbc3c 1709
aa971cb9 1710[[getting-updates-With-git-pull]]
6127c086 1711Getting updates with git pull
b684f830 1712-----------------------------
d19fbc3c 1713
e63ec003 1714After you clone a repository and commit a few changes of your own, you
d19fbc3c
BF
1715may wish to check the original repository for updates and merge them
1716into your own work.
1717
aa971cb9 1718We have already seen <<Updating-a-repository-With-git-fetch,how to
0e615b25 1719keep remote-tracking branches up to date>> with linkgit:git-fetch[1],
d19fbc3c
BF
1720and how to merge two branches. So you can merge in changes from the
1721original repository's master branch with:
1722
1723-------------------------------------------------
1724$ git fetch
1725$ git merge origin/master
1726-------------------------------------------------
1727
5162e697 1728However, the linkgit:git-pull[1] command provides a way to do this in
d19fbc3c
BF
1729one step:
1730
1731-------------------------------------------------
1732$ git pull origin master
1733-------------------------------------------------
1734
66a062a1
MM
1735In fact, if you have "master" checked out, then this branch has been
1736configured by "git clone" to get changes from the HEAD branch of the
1737origin repository. So often you can
0eb4f7cd 1738accomplish the above with just a simple
d19fbc3c
BF
1739
1740-------------------------------------------------
1741$ git pull
1742-------------------------------------------------
1743
66a062a1
MM
1744This command will fetch changes from the remote branches to your
1745remote-tracking branches `origin/*`, and merge the default branch into
1746the current branch.
1747
29b9a66f
MM
1748More generally, a branch that is created from a remote-tracking branch
1749will pull
0eb4f7cd
BF
1750by default from that branch. See the descriptions of the
1751branch.<name>.remote and branch.<name>.merge options in
5162e697
DM
1752linkgit:git-config[1], and the discussion of the `--track` option in
1753linkgit:git-checkout[1], to learn how to control these defaults.
d19fbc3c
BF
1754
1755In addition to saving you keystrokes, "git pull" also helps you by
1756producing a default commit message documenting the branch and
1757repository that you pulled from.
1758
1759(But note that no such commit will be created in the case of a
a75d7b54 1760<<fast-forwards,fast-forward>>; instead, your branch will just be
79c96c57 1761updated to point to the latest commit from the upstream branch.)
d19fbc3c 1762
6127c086 1763The `git pull` command can also be given "." as the "remote" repository,
1191ee18 1764in which case it just merges in a branch from the current repository; so
4c63ff45
BF
1765the commands
1766
1767-------------------------------------------------
1768$ git pull . branch
1769$ git merge branch
1770-------------------------------------------------
1771
1772are roughly equivalent. The former is actually very commonly used.
1773
e34caace 1774[[submitting-patches]]
d19fbc3c 1775Submitting patches to a project
b684f830 1776-------------------------------
d19fbc3c
BF
1777
1778If you just have a few changes, the simplest way to submit them may
1779just be to send them as patches in email:
1780
5162e697 1781First, use linkgit:git-format-patch[1]; for example:
d19fbc3c
BF
1782
1783-------------------------------------------------
eb6ae7f4 1784$ git format-patch origin
d19fbc3c
BF
1785-------------------------------------------------
1786
1787will produce a numbered series of files in the current directory, one
1788for each patch in the current branch but not in origin/HEAD.
1789
1790You can then import these into your mail client and send them by
1791hand. However, if you have a lot to send at once, you may prefer to
5162e697 1792use the linkgit:git-send-email[1] script to automate the process.
d19fbc3c
BF
1793Consult the mailing list for your project first to determine how they
1794prefer such patches be handled.
1795
e34caace 1796[[importing-patches]]
d19fbc3c 1797Importing patches to a project
b684f830 1798------------------------------
d19fbc3c 1799
5162e697 1800Git also provides a tool called linkgit:git-am[1] (am stands for
d19fbc3c
BF
1801"apply mailbox"), for importing such an emailed series of patches.
1802Just save all of the patch-containing messages, in order, into a
1803single mailbox file, say "patches.mbox", then run
1804
1805-------------------------------------------------
eb6ae7f4 1806$ git am -3 patches.mbox
d19fbc3c
BF
1807-------------------------------------------------
1808
1809Git will apply each patch in order; if any conflicts are found, it
1810will stop, and you can fix the conflicts as described in
01997b4a
BF
1811"<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells
1812git to perform a merge; if you would prefer it just to abort and
1813leave your tree and index untouched, you may omit that option.)
1814
1815Once the index is updated with the results of the conflict
1816resolution, instead of creating a new commit, just run
d19fbc3c
BF
1817
1818-------------------------------------------------
1819$ git am --resolved
1820-------------------------------------------------
1821
1822and git will create the commit for you and continue applying the
1823remaining patches from the mailbox.
1824
1825The final result will be a series of commits, one for each patch in
1826the original mailbox, with authorship and commit log message each
1827taken from the message containing each patch.
1828
eda69449
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1829[[public-repositories]]
1830Public git repositories
1831-----------------------
d19fbc3c 1832
6e30fb0c
DK
1833Another way to submit changes to a project is to tell the maintainer
1834of that project to pull the changes from your repository using
aa971cb9 1835linkgit:git-pull[1]. In the section "<<getting-updates-With-git-pull,
6127c086 1836Getting updates with `git pull`>>" we described this as a way to get
6e30fb0c
DK
1837updates from the "main" repository, but it works just as well in the
1838other direction.
d19fbc3c 1839
eda69449
BF
1840If you and the maintainer both have accounts on the same machine, then
1841you can just pull changes from each other's repositories directly;
11d51533 1842commands that accept repository URLs as arguments will also accept a
eda69449 1843local directory name:
d19fbc3c
BF
1844
1845-------------------------------------------------
1846$ git clone /path/to/repository
1847$ git pull /path/to/other/repository
1848-------------------------------------------------
1849
c9016158 1850or an ssh URL:
11d51533
BF
1851
1852-------------------------------------------------
1853$ git clone ssh://yourhost/~you/repository
1854-------------------------------------------------
1855
1856For projects with few developers, or for synchronizing a few private
1857repositories, this may be all you need.
1858
eda69449
BF
1859However, the more common way to do this is to maintain a separate public
1860repository (usually on a different host) for others to pull changes
1861from. This is usually more convenient, and allows you to cleanly
1862separate private work in progress from publicly visible work.
d19fbc3c
BF
1863
1864You will continue to do your day-to-day work in your personal
1865repository, but periodically "push" changes from your personal
1866repository into your public repository, allowing other developers to
1867pull from that repository. So the flow of changes, in a situation
1868where there is one other developer with a public repository, looks
1869like this:
1870
1871 you push
1872 your personal repo ------------------> your public repo
a6080a0a 1873 ^ |
d19fbc3c
BF
1874 | |
1875 | you pull | they pull
1876 | |
1877 | |
1878 | they push V
1879 their public repo <------------------- their repo
1880
11d51533
BF
1881We explain how to do this in the following sections.
1882
eda69449
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1883[[setting-up-a-public-repository]]
1884Setting up a public repository
1885~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1886
1887Assume your personal repository is in the directory ~/proj. We
6127c086 1888first create a new clone of the repository and tell `git daemon` that it
eda69449 1889is meant to be public:
d19fbc3c
BF
1890
1891-------------------------------------------------
52c80037 1892$ git clone --bare ~/proj proj.git
eda69449 1893$ touch proj.git/git-daemon-export-ok
d19fbc3c
BF
1894-------------------------------------------------
1895
52c80037 1896The resulting directory proj.git contains a "bare" git repository--it is
eda69449
BF
1897just the contents of the ".git" directory, without any files checked out
1898around it.
d19fbc3c 1899
c64415e2 1900Next, copy proj.git to the server where you plan to host the
d19fbc3c
BF
1901public repository. You can use scp, rsync, or whatever is most
1902convenient.
1903
eda69449
BF
1904[[exporting-via-git]]
1905Exporting a git repository via the git protocol
1906~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1907
1908This is the preferred method.
1909
1910If someone else administers the server, they should tell you what
c9016158 1911directory to put the repository in, and what git:// URL it will appear
eda69449 1912at. You can then skip to the section
d19fbc3c
BF
1913"<<pushing-changes-to-a-public-repository,Pushing changes to a public
1914repository>>", below.
1915
5162e697 1916Otherwise, all you need to do is start linkgit:git-daemon[1]; it will
eda69449
BF
1917listen on port 9418. By default, it will allow access to any directory
1918that looks like a git directory and contains the magic file
6127c086 1919git-daemon-export-ok. Passing some directory paths as `git daemon`
eda69449
BF
1920arguments will further restrict the exports to those paths.
1921
6127c086 1922You can also run `git daemon` as an inetd service; see the
5162e697 1923linkgit:git-daemon[1] man page for details. (See especially the
eda69449 1924examples section.)
d19fbc3c
BF
1925
1926[[exporting-via-http]]
1927Exporting a git repository via http
eda69449 1928~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
1929
1930The git protocol gives better performance and reliability, but on a
1931host with a web server set up, http exports may be simpler to set up.
1932
1933All you need to do is place the newly created bare git repository in
1934a directory that is exported by the web server, and make some
1935adjustments to give web clients some extra information they need:
1936
1937-------------------------------------------------
1938$ mv proj.git /home/you/public_html/proj.git
1939$ cd proj.git
c64415e2 1940$ git --bare update-server-info
7dce9918 1941$ mv hooks/post-update.sample hooks/post-update
d19fbc3c
BF
1942-------------------------------------------------
1943
1944(For an explanation of the last two lines, see
6998e4db 1945linkgit:git-update-server-info[1] and linkgit:githooks[5].)
d19fbc3c 1946
c9016158
RW
1947Advertise the URL of proj.git. Anybody else should then be able to
1948clone or pull from that URL, for example with a command line like:
d19fbc3c
BF
1949
1950-------------------------------------------------
1951$ git clone http://yourserver.com/~you/proj.git
1952-------------------------------------------------
1953
1954(See also
1955link:howto/setup-git-server-over-http.txt[setup-git-server-over-http]
1956for a slightly more sophisticated setup using WebDAV which also
1957allows pushing over http.)
1958
d19fbc3c
BF
1959[[pushing-changes-to-a-public-repository]]
1960Pushing changes to a public repository
eda69449 1961~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 1962
eda69449 1963Note that the two techniques outlined above (exporting via
d19fbc3c
BF
1964<<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other
1965maintainers to fetch your latest changes, but they do not allow write
1966access, which you will need to update the public repository with the
1967latest changes created in your private repository.
1968
5162e697 1969The simplest way to do this is using linkgit:git-push[1] and ssh; to
d19fbc3c
BF
1970update the remote branch named "master" with the latest state of your
1971branch named "master", run
1972
1973-------------------------------------------------
1974$ git push ssh://yourserver.com/~you/proj.git master:master
1975-------------------------------------------------
1976
1977or just
1978
1979-------------------------------------------------
1980$ git push ssh://yourserver.com/~you/proj.git master
1981-------------------------------------------------
1982
6127c086 1983As with `git fetch`, `git push` will complain if this does not result in a
a75d7b54 1984<<fast-forwards,fast-forward>>; see the following section for details on
81eb417a 1985handling this case.
d19fbc3c 1986
11d51533
BF
1987Note that the target of a "push" is normally a
1988<<def_bare_repository,bare>> repository. You can also push to a
d9be2485
TK
1989repository that has a checked-out working tree, but a push to update the
1990currently checked-out branch is denied by default to prevent confusion.
1991See the description ofthe receive.denyCurrentBranch option
1992in linkgit:git-config[1] for details.
11d51533 1993
6127c086 1994As with `git fetch`, you may also set up configuration options to
d19fbc3c
BF
1995save typing; so, for example, after
1996
1997-------------------------------------------------
c64415e2 1998$ cat >>.git/config <<EOF
d19fbc3c
BF
1999[remote "public-repo"]
2000 url = ssh://yourserver.com/~you/proj.git
2001EOF
2002-------------------------------------------------
2003
2004you should be able to perform the above push with just
2005
2006-------------------------------------------------
2007$ git push public-repo master
2008-------------------------------------------------
2009
2010See the explanations of the remote.<name>.url, branch.<name>.remote,
5162e697 2011and remote.<name>.push options in linkgit:git-config[1] for
d19fbc3c
BF
2012details.
2013
81eb417a
BF
2014[[forcing-push]]
2015What to do when a push fails
2016~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2017
a75d7b54 2018If a push would not result in a <<fast-forwards,fast-forward>> of the
81eb417a
BF
2019remote branch, then it will fail with an error like:
2020
2021-------------------------------------------------
2022error: remote 'refs/heads/master' is not an ancestor of
2023 local 'refs/heads/master'.
2024 Maybe you are not up-to-date and need to pull first?
2025error: failed to push to 'ssh://yourserver.com/~you/proj.git'
2026-------------------------------------------------
2027
2028This can happen, for example, if you:
2029
6127c086
FC
2030 - use `git reset --hard` to remove already-published commits, or
2031 - use `git commit --amend` to replace already-published commits
7cb192ea 2032 (as in <<fixing-a-mistake-by-rewriting-history>>), or
6127c086 2033 - use `git rebase` to rebase any already-published commits (as
81eb417a
BF
2034 in <<using-git-rebase>>).
2035
6127c086 2036You may force `git push` to perform the update anyway by preceding the
81eb417a
BF
2037branch name with a plus sign:
2038
2039-------------------------------------------------
2040$ git push ssh://yourserver.com/~you/proj.git +master
2041-------------------------------------------------
2042
2043Normally whenever a branch head in a public repository is modified, it
9e5d87d4 2044is modified to point to a descendant of the commit that it pointed to
81eb417a 2045before. By forcing a push in this situation, you break that convention.
aa971cb9 2046(See <<problems-With-rewriting-history>>.)
81eb417a
BF
2047
2048Nevertheless, this is a common practice for people that need a simple
2049way to publish a work-in-progress patch series, and it is an acceptable
2050compromise as long as you warn other developers that this is how you
2051intend to manage the branch.
2052
2053It's also possible for a push to fail in this way when other people have
2054the right to push to the same repository. In that case, the correct
843c81dc
EH
2055solution is to retry the push after first updating your work: either by a
2056pull, or by a fetch followed by a rebase; see the
81eb417a 2057<<setting-up-a-shared-repository,next section>> and
6998e4db 2058linkgit:gitcvs-migration[7] for more.
81eb417a 2059
e34caace 2060[[setting-up-a-shared-repository]]
d19fbc3c 2061Setting up a shared repository
eda69449 2062~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
2063
2064Another way to collaborate is by using a model similar to that
2065commonly used in CVS, where several developers with special rights
2066all push to and pull from a single shared repository. See
6998e4db 2067linkgit:gitcvs-migration[7] for instructions on how to
d19fbc3c
BF
2068set this up.
2069
8fae2225
BF
2070However, while there is nothing wrong with git's support for shared
2071repositories, this mode of operation is not generally recommended,
2072simply because the mode of collaboration that git supports--by
2073exchanging patches and pulling from public repositories--has so many
2074advantages over the central shared repository:
2075
2076 - Git's ability to quickly import and merge patches allows a
2077 single maintainer to process incoming changes even at very
6127c086 2078 high rates. And when that becomes too much, `git pull` provides
8fae2225
BF
2079 an easy way for that maintainer to delegate this job to other
2080 maintainers while still allowing optional review of incoming
2081 changes.
2082 - Since every developer's repository has the same complete copy
2083 of the project history, no repository is special, and it is
2084 trivial for another developer to take over maintenance of a
2085 project, either by mutual agreement, or because a maintainer
2086 becomes unresponsive or difficult to work with.
2087 - The lack of a central group of "committers" means there is
2088 less need for formal decisions about who is "in" and who is
2089 "out".
2090
e34caace 2091[[setting-up-gitweb]]
eda69449
BF
2092Allowing web browsing of a repository
2093~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 2094
a8cd1402
BF
2095The gitweb cgi script provides users an easy way to browse your
2096project's files and history without having to install git; see the file
04483524 2097gitweb/INSTALL in the git source tree for instructions on setting it up.
d19fbc3c 2098
e34caace 2099[[sharing-development-examples]]
b684f830
BF
2100Examples
2101--------
d19fbc3c 2102
9e2163ea
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2103[[maintaining-topic-branches]]
2104Maintaining topic branches for a Linux subsystem maintainer
2105~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2106
2107This describes how Tony Luck uses git in his role as maintainer of the
2108IA64 architecture for the Linux kernel.
2109
2110He uses two public branches:
2111
2112 - A "test" tree into which patches are initially placed so that they
2113 can get some exposure when integrated with other ongoing development.
2114 This tree is available to Andrew for pulling into -mm whenever he
2115 wants.
2116
2117 - A "release" tree into which tested patches are moved for final sanity
2118 checking, and as a vehicle to send them upstream to Linus (by sending
2119 him a "please pull" request.)
2120
2121He also uses a set of temporary branches ("topic branches"), each
2122containing a logical grouping of patches.
2123
2124To set this up, first create your work tree by cloning Linus's public
2125tree:
2126
2127-------------------------------------------------
2128$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work
2129$ cd work
2130-------------------------------------------------
2131
29b9a66f 2132Linus's tree will be stored in the remote-tracking branch named origin/master,
5162e697
DM
2133and can be updated using linkgit:git-fetch[1]; you can track other
2134public trees using linkgit:git-remote[1] to set up a "remote" and
2135linkgit:git-fetch[1] to keep them up-to-date; see
6e30fb0c 2136<<repositories-and-branches>>.
9e2163ea
BF
2137
2138Now create the branches in which you are going to work; these start out
2139at the current tip of origin/master branch, and should be set up (using
5162e697 2140the --track option to linkgit:git-branch[1]) to merge changes in from
9e2163ea
BF
2141Linus by default.
2142
2143-------------------------------------------------
2144$ git branch --track test origin/master
2145$ git branch --track release origin/master
2146-------------------------------------------------
2147
5162e697 2148These can be easily kept up to date using linkgit:git-pull[1].
9e2163ea
BF
2149
2150-------------------------------------------------
2151$ git checkout test && git pull
2152$ git checkout release && git pull
2153-------------------------------------------------
2154
2155Important note! If you have any local changes in these branches, then
2156this merge will create a commit object in the history (with no local
a75d7b54 2157changes git will simply do a "fast-forward" merge). Many people dislike
9e2163ea
BF
2158the "noise" that this creates in the Linux history, so you should avoid
2159doing this capriciously in the "release" branch, as these noisy commits
2160will become part of the permanent history when you ask Linus to pull
2161from the release branch.
2162
5162e697 2163A few configuration variables (see linkgit:git-config[1]) can
9e2163ea
BF
2164make it easy to push both branches to your public tree. (See
2165<<setting-up-a-public-repository>>.)
2166
2167-------------------------------------------------
2168$ cat >> .git/config <<EOF
2169[remote "mytree"]
2170 url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
2171 push = release
2172 push = test
2173EOF
2174-------------------------------------------------
2175
2176Then you can push both the test and release trees using
5162e697 2177linkgit:git-push[1]:
9e2163ea
BF
2178
2179-------------------------------------------------
2180$ git push mytree
2181-------------------------------------------------
2182
2183or push just one of the test and release branches using:
2184
2185-------------------------------------------------
2186$ git push mytree test
2187-------------------------------------------------
2188
2189or
2190
2191-------------------------------------------------
2192$ git push mytree release
2193-------------------------------------------------
2194
2195Now to apply some patches from the community. Think of a short
2196snappy name for a branch to hold this patch (or related group of
352953a5
TL
2197patches), and create a new branch from a recent stable tag of
2198Linus's branch. Picking a stable base for your branch will:
21991) help you: by avoiding inclusion of unrelated and perhaps lightly
2200tested changes
22012) help future bug hunters that use "git bisect" to find problems
9e2163ea
BF
2202
2203-------------------------------------------------
352953a5 2204$ git checkout -b speed-up-spinlocks v2.6.35
9e2163ea
BF
2205-------------------------------------------------
2206
2207Now you apply the patch(es), run some tests, and commit the change(s). If
2208the patch is a multi-part series, then you should apply each as a separate
2209commit to this branch.
2210
2211-------------------------------------------------
2212$ ... patch ... test ... commit [ ... patch ... test ... commit ]*
2213-------------------------------------------------
2214
2215When you are happy with the state of this change, you can pull it into the
2216"test" branch in preparation to make it public:
2217
2218-------------------------------------------------
2219$ git checkout test && git pull . speed-up-spinlocks
2220-------------------------------------------------
2221
2222It is unlikely that you would have any conflicts here ... but you might if you
2223spent a while on this step and had also pulled new versions from upstream.
2224
2225Some time later when enough time has passed and testing done, you can pull the
2226same branch into the "release" tree ready to go upstream. This is where you
2227see the value of keeping each patch (or patch series) in its own branch. It
2228means that the patches can be moved into the "release" tree in any order.
2229
2230-------------------------------------------------
2231$ git checkout release && git pull . speed-up-spinlocks
2232-------------------------------------------------
2233
2234After a while, you will have a number of branches, and despite the
2235well chosen names you picked for each of them, you may forget what
2236they are for, or what status they are in. To get a reminder of what
2237changes are in a specific branch, use:
2238
2239-------------------------------------------------
467c0197 2240$ git log linux..branchname | git shortlog
9e2163ea
BF
2241-------------------------------------------------
2242
06ada152 2243To see whether it has already been merged into the test or release branches,
9e2163ea
BF
2244use:
2245
2246-------------------------------------------------
2247$ git log test..branchname
2248-------------------------------------------------
2249
2250or
2251
2252-------------------------------------------------
2253$ git log release..branchname
2254-------------------------------------------------
2255
06ada152 2256(If this branch has not yet been merged, you will see some log entries.
9e2163ea
BF
2257If it has been merged, then there will be no output.)
2258
2259Once a patch completes the great cycle (moving from test to release,
2260then pulled by Linus, and finally coming back into your local
06ada152 2261"origin/master" branch), the branch for this change is no longer needed.
9e2163ea
BF
2262You detect this when the output from:
2263
2264-------------------------------------------------
2265$ git log origin..branchname
2266-------------------------------------------------
2267
2268is empty. At this point the branch can be deleted:
2269
2270-------------------------------------------------
2271$ git branch -d branchname
2272-------------------------------------------------
2273
2274Some changes are so trivial that it is not necessary to create a separate
2275branch and then merge into each of the test and release branches. For
2276these changes, just apply directly to the "release" branch, and then
2277merge that into the "test" branch.
2278
2279To create diffstat and shortlog summaries of changes to include in a "please
2280pull" request to Linus you can use:
2281
2282-------------------------------------------------
2283$ git diff --stat origin..release
2284-------------------------------------------------
2285
2286and
2287
2288-------------------------------------------------
2289$ git log -p origin..release | git shortlog
2290-------------------------------------------------
2291
2292Here are some of the scripts that simplify all this even further.
2293
2294-------------------------------------------------
2295==== update script ====
2296# Update a branch in my GIT tree. If the branch to be updated
2297# is origin, then pull from kernel.org. Otherwise merge
2298# origin/master branch into test|release branch
2299
2300case "$1" in
2301test|release)
2302 git checkout $1 && git pull . origin
2303 ;;
2304origin)
fc74ecc1 2305 before=$(git rev-parse refs/remotes/origin/master)
9e2163ea 2306 git fetch origin
fc74ecc1 2307 after=$(git rev-parse refs/remotes/origin/master)
9e2163ea
BF
2308 if [ $before != $after ]
2309 then
2310 git log $before..$after | git shortlog
2311 fi
2312 ;;
2313*)
2314 echo "Usage: $0 origin|test|release" 1>&2
2315 exit 1
2316 ;;
2317esac
2318-------------------------------------------------
2319
2320-------------------------------------------------
2321==== merge script ====
2322# Merge a branch into either the test or release branch
2323
2324pname=$0
2325
2326usage()
2327{
2328 echo "Usage: $pname branch test|release" 1>&2
2329 exit 1
2330}
2331
fc74ecc1 2332git show-ref -q --verify -- refs/heads/"$1" || {
9e2163ea
BF
2333 echo "Can't see branch <$1>" 1>&2
2334 usage
fc74ecc1 2335}
9e2163ea
BF
2336
2337case "$2" in
2338test|release)
2339 if [ $(git log $2..$1 | wc -c) -eq 0 ]
2340 then
2341 echo $1 already merged into $2 1>&2
2342 exit 1
2343 fi
2344 git checkout $2 && git pull . $1
2345 ;;
2346*)
2347 usage
2348 ;;
2349esac
2350-------------------------------------------------
2351
2352-------------------------------------------------
2353==== status script ====
2354# report on status of my ia64 GIT tree
2355
2356gb=$(tput setab 2)
2357rb=$(tput setab 1)
2358restore=$(tput setab 9)
2359
2360if [ `git rev-list test..release | wc -c` -gt 0 ]
2361then
2362 echo $rb Warning: commits in release that are not in test $restore
2363 git log test..release
2364fi
2365
fc74ecc1 2366for branch in `git show-ref --heads | sed 's|^.*/||'`
9e2163ea
BF
2367do
2368 if [ $branch = test -o $branch = release ]
2369 then
2370 continue
2371 fi
2372
2373 echo -n $gb ======= $branch ====== $restore " "
2374 status=
2375 for ref in test release origin/master
2376 do
2377 if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]
2378 then
2379 status=$status${ref:0:1}
2380 fi
2381 done
2382 case $status in
2383 trl)
2384 echo $rb Need to pull into test $restore
2385 ;;
2386 rl)
2387 echo "In test"
2388 ;;
2389 l)
2390 echo "Waiting for linus"
2391 ;;
2392 "")
2393 echo $rb All done $restore
2394 ;;
2395 *)
2396 echo $rb "<$status>" $restore
2397 ;;
2398 esac
2399 git log origin/master..$branch | git shortlog
2400done
2401-------------------------------------------------
d19fbc3c 2402
d19fbc3c 2403
d19fbc3c 2404[[cleaning-up-history]]
4c63ff45
BF
2405Rewriting history and maintaining patch series
2406==============================================
2407
2408Normally commits are only added to a project, never taken away or
2409replaced. Git is designed with this assumption, and violating it will
2410cause git's merge machinery (for example) to do the wrong thing.
2411
2412However, there is a situation in which it can be useful to violate this
2413assumption.
2414
e34caace 2415[[patch-series]]
4c63ff45
BF
2416Creating the perfect patch series
2417---------------------------------
2418
2419Suppose you are a contributor to a large project, and you want to add a
2420complicated feature, and to present it to the other developers in a way
2421that makes it easy for them to read your changes, verify that they are
2422correct, and understand why you made each change.
2423
b181d57f 2424If you present all of your changes as a single patch (or commit), they
79c96c57 2425may find that it is too much to digest all at once.
4c63ff45
BF
2426
2427If you present them with the entire history of your work, complete with
2428mistakes, corrections, and dead ends, they may be overwhelmed.
2429
2430So the ideal is usually to produce a series of patches such that:
2431
2432 1. Each patch can be applied in order.
2433
2434 2. Each patch includes a single logical change, together with a
2435 message explaining the change.
2436
2437 3. No patch introduces a regression: after applying any initial
2438 part of the series, the resulting project still compiles and
2439 works, and has no bugs that it didn't have before.
2440
2441 4. The complete series produces the same end result as your own
2442 (probably much messier!) development process did.
2443
b181d57f
BF
2444We will introduce some tools that can help you do this, explain how to
2445use them, and then explain some of the problems that can arise because
2446you are rewriting history.
4c63ff45 2447
e34caace 2448[[using-git-rebase]]
6127c086 2449Keeping a patch series up to date using git rebase
4c63ff45
BF
2450--------------------------------------------------
2451
79c96c57
MC
2452Suppose that you create a branch "mywork" on a remote-tracking branch
2453"origin", and create some commits on top of it:
4c63ff45
BF
2454
2455-------------------------------------------------
2456$ git checkout -b mywork origin
2457$ vi file.txt
2458$ git commit
2459$ vi otherfile.txt
2460$ git commit
2461...
2462-------------------------------------------------
2463
2464You have performed no merges into mywork, so it is just a simple linear
2465sequence of patches on top of "origin":
2466
1dc71a91 2467................................................
fa8347b8 2468 o--o--O <-- origin
4c63ff45 2469 \
fa8347b8 2470 a--b--c <-- mywork
1dc71a91 2471................................................
4c63ff45
BF
2472
2473Some more interesting work has been done in the upstream project, and
2474"origin" has advanced:
2475
1dc71a91 2476................................................
4c63ff45
BF
2477 o--o--O--o--o--o <-- origin
2478 \
2479 a--b--c <-- mywork
1dc71a91 2480................................................
4c63ff45
BF
2481
2482At this point, you could use "pull" to merge your changes back in;
2483the result would create a new merge commit, like this:
2484
1dc71a91 2485................................................
4c63ff45
BF
2486 o--o--O--o--o--o <-- origin
2487 \ \
2488 a--b--c--m <-- mywork
1dc71a91 2489................................................
a6080a0a 2490
4c63ff45
BF
2491However, if you prefer to keep the history in mywork a simple series of
2492commits without any merges, you may instead choose to use
5162e697 2493linkgit:git-rebase[1]:
4c63ff45
BF
2494
2495-------------------------------------------------
2496$ git checkout mywork
2497$ git rebase origin
2498-------------------------------------------------
2499
b181d57f 2500This will remove each of your commits from mywork, temporarily saving
51ef1daa 2501them as patches (in a directory named ".git/rebase-apply"), update mywork to
b181d57f
BF
2502point at the latest version of origin, then apply each of the saved
2503patches to the new mywork. The result will look like:
4c63ff45
BF
2504
2505
1dc71a91 2506................................................
4c63ff45
BF
2507 o--o--O--o--o--o <-- origin
2508 \
2509 a'--b'--c' <-- mywork
1dc71a91 2510................................................
4c63ff45 2511
b181d57f 2512In the process, it may discover conflicts. In that case it will stop
6127c086 2513and allow you to fix the conflicts; after fixing conflicts, use `git add`
7a7d4ef6 2514to update the index with those contents, and then, instead of
6127c086 2515running `git commit`, just run
4c63ff45
BF
2516
2517-------------------------------------------------
2518$ git rebase --continue
2519-------------------------------------------------
2520
2521and git will continue applying the rest of the patches.
2522
b6cbca38 2523At any point you may use the `--abort` option to abort this process and
4c63ff45
BF
2524return mywork to the state it had before you started the rebase:
2525
2526-------------------------------------------------
2527$ git rebase --abort
2528-------------------------------------------------
2529
7cb192ea
BF
2530[[rewriting-one-commit]]
2531Rewriting a single commit
365aa199
BF
2532-------------------------
2533
7cb192ea 2534We saw in <<fixing-a-mistake-by-rewriting-history>> that you can replace the
365aa199
BF
2535most recent commit using
2536
2537-------------------------------------------------
2538$ git commit --amend
2539-------------------------------------------------
2540
2541which will replace the old commit by a new commit incorporating your
2542changes, giving you a chance to edit the old commit message first.
2543
5162e697 2544You can also use a combination of this and linkgit:git-rebase[1] to
7cb192ea
BF
2545replace a commit further back in your history and recreate the
2546intervening changes on top of it. First, tag the problematic commit
2547with
365aa199
BF
2548
2549-------------------------------------------------
2550$ git tag bad mywork~5
2551-------------------------------------------------
2552
6127c086 2553(Either gitk or `git log` may be useful for finding the commit.)
365aa199 2554
25d9f3fa
BF
2555Then check out that commit, edit it, and rebase the rest of the series
2556on top of it (note that we could check out the commit on a temporary
2557branch, but instead we're using a <<detached-head,detached head>>):
365aa199
BF
2558
2559-------------------------------------------------
25d9f3fa 2560$ git checkout bad
365aa199
BF
2561$ # make changes here and update the index
2562$ git commit --amend
25d9f3fa 2563$ git rebase --onto HEAD bad mywork
365aa199
BF
2564-------------------------------------------------
2565
25d9f3fa
BF
2566When you're done, you'll be left with mywork checked out, with the top
2567patches on mywork reapplied on top of your modified commit. You can
365aa199
BF
2568then clean up with
2569
2570-------------------------------------------------
365aa199
BF
2571$ git tag -d bad
2572-------------------------------------------------
2573
2574Note that the immutable nature of git history means that you haven't really
2575"modified" existing commits; instead, you have replaced the old commits with
2576new commits having new object names.
2577
e34caace 2578[[reordering-patch-series]]
4c63ff45
BF
2579Reordering or selecting from a patch series
2580-------------------------------------------
2581
5162e697 2582Given one existing commit, the linkgit:git-cherry-pick[1] command
b181d57f
BF
2583allows you to apply the change introduced by that commit and create a
2584new commit that records it. So, for example, if "mywork" points to a
2585series of patches on top of "origin", you might do something like:
2586
2587-------------------------------------------------
2588$ git checkout -b mywork-new origin
2589$ gitk origin..mywork &
2590-------------------------------------------------
2591
06ada152 2592and browse through the list of patches in the mywork branch using gitk,
b181d57f 2593applying them (possibly in a different order) to mywork-new using
6127c086 2594cherry-pick, and possibly modifying them as you go using `git commit --amend`.
5162e697 2595The linkgit:git-gui[1] command may also help as it allows you to
6e30fb0c
DK
2596individually select diff hunks for inclusion in the index (by
2597right-clicking on the diff hunk and choosing "Stage Hunk for Commit").
b181d57f 2598
6127c086 2599Another technique is to use `git format-patch` to create a series of
b181d57f 2600patches, then reset the state to before the patches:
4c63ff45 2601
b181d57f
BF
2602-------------------------------------------------
2603$ git format-patch origin
2604$ git reset --hard origin
2605-------------------------------------------------
4c63ff45 2606
b181d57f 2607Then modify, reorder, or eliminate patches as preferred before applying
5162e697 2608them again with linkgit:git-am[1].
4c63ff45 2609
e34caace 2610[[patch-series-tools]]
4c63ff45
BF
2611Other tools
2612-----------
2613
73a1d050 2614There are numerous other tools, such as StGit, which exist for the
79c96c57 2615purpose of maintaining a patch series. These are outside of the scope of
b181d57f 2616this manual.
4c63ff45 2617
aa971cb9 2618[[problems-With-rewriting-history]]
4c63ff45
BF
2619Problems with rewriting history
2620-------------------------------
2621
b181d57f
BF
2622The primary problem with rewriting the history of a branch has to do
2623with merging. Suppose somebody fetches your branch and merges it into
2624their branch, with a result something like this:
2625
1dc71a91 2626................................................
b181d57f
BF
2627 o--o--O--o--o--o <-- origin
2628 \ \
2629 t--t--t--m <-- their branch:
1dc71a91 2630................................................
b181d57f
BF
2631
2632Then suppose you modify the last three commits:
2633
1dc71a91 2634................................................
b181d57f
BF
2635 o--o--o <-- new head of origin
2636 /
2637 o--o--O--o--o--o <-- old head of origin
1dc71a91 2638................................................
b181d57f
BF
2639
2640If we examined all this history together in one repository, it will
2641look like:
2642
1dc71a91 2643................................................
b181d57f
BF
2644 o--o--o <-- new head of origin
2645 /
2646 o--o--O--o--o--o <-- old head of origin
2647 \ \
2648 t--t--t--m <-- their branch:
1dc71a91 2649................................................
b181d57f
BF
2650
2651Git has no way of knowing that the new head is an updated version of
2652the old head; it treats this situation exactly the same as it would if
2653two developers had independently done the work on the old and new heads
2654in parallel. At this point, if someone attempts to merge the new head
2655in to their branch, git will attempt to merge together the two (old and
2656new) lines of development, instead of trying to replace the old by the
2657new. The results are likely to be unexpected.
2658
2659You may still choose to publish branches whose history is rewritten,
2660and it may be useful for others to be able to fetch those branches in
2661order to examine or test them, but they should not attempt to pull such
2662branches into their own work.
2663
2664For true distributed development that supports proper merging,
2665published branches should never be rewritten.
2666
3fb00282
SP
2667[[bisect-merges]]
2668Why bisecting merge commits can be harder than bisecting linear history
2669-----------------------------------------------------------------------
2670
5162e697 2671The linkgit:git-bisect[1] command correctly handles history that
3fb00282
SP
2672includes merge commits. However, when the commit that it finds is a
2673merge commit, the user may need to work harder than usual to figure out
2674why that commit introduced a problem.
2675
2676Imagine this history:
2677
2678................................................
2679 ---Z---o---X---...---o---A---C---D
2680 \ /
2681 o---o---Y---...---o---B
2682................................................
2683
2684Suppose that on the upper line of development, the meaning of one
2685of the functions that exists at Z is changed at commit X. The
2686commits from Z leading to A change both the function's
2687implementation and all calling sites that exist at Z, as well
2688as new calling sites they add, to be consistent. There is no
2689bug at A.
2690
2691Suppose that in the meantime on the lower line of development somebody
2692adds a new calling site for that function at commit Y. The
2693commits from Z leading to B all assume the old semantics of that
2694function and the callers and the callee are consistent with each
2695other. There is no bug at B, either.
2696
2697Suppose further that the two development lines merge cleanly at C,
2698so no conflict resolution is required.
2699
2700Nevertheless, the code at C is broken, because the callers added
2701on the lower line of development have not been converted to the new
2702semantics introduced on the upper line of development. So if all
2703you know is that D is bad, that Z is good, and that
5162e697 2704linkgit:git-bisect[1] identifies C as the culprit, how will you
3fb00282
SP
2705figure out that the problem is due to this change in semantics?
2706
6127c086 2707When the result of a `git bisect` is a non-merge commit, you should
3fb00282
SP
2708normally be able to discover the problem by examining just that commit.
2709Developers can make this easy by breaking their changes into small
2710self-contained commits. That won't help in the case above, however,
2711because the problem isn't obvious from examination of any single
2712commit; instead, a global view of the development is required. To
2713make matters worse, the change in semantics in the problematic
2714function may be just one small part of the changes in the upper
2715line of development.
2716
2717On the other hand, if instead of merging at C you had rebased the
2718history between Z to B on top of A, you would have gotten this
2719linear history:
2720
2721................................................................
2722 ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D*
2723................................................................
2724
2725Bisecting between Z and D* would hit a single culprit commit Y*,
2726and understanding why Y* was broken would probably be easier.
2727
2728Partly for this reason, many experienced git users, even when
2729working on an otherwise merge-heavy project, keep the history
2730linear by rebasing against the latest upstream version before
2731publishing.
2732
e34caace 2733[[advanced-branch-management]]
b181d57f
BF
2734Advanced branch management
2735==========================
4c63ff45 2736
e34caace 2737[[fetching-individual-branches]]
b181d57f
BF
2738Fetching individual branches
2739----------------------------
2740
5162e697 2741Instead of using linkgit:git-remote[1], you can also choose just
b181d57f
BF
2742to update one branch at a time, and to store it locally under an
2743arbitrary name:
2744
2745-------------------------------------------------
2746$ git fetch origin todo:my-todo-work
2747-------------------------------------------------
2748
2749The first argument, "origin", just tells git to fetch from the
2750repository you originally cloned from. The second argument tells git
2751to fetch the branch named "todo" from the remote repository, and to
2752store it locally under the name refs/heads/my-todo-work.
2753
2754You can also fetch branches from other repositories; so
2755
2756-------------------------------------------------
2757$ git fetch git://example.com/proj.git master:example-master
2758-------------------------------------------------
2759
2760will create a new branch named "example-master" and store in it the
2761branch named "master" from the repository at the given URL. If you
2762already have a branch named example-master, it will attempt to
59723040
BF
2763<<fast-forwards,fast-forward>> to the commit given by example.com's
2764master branch. In more detail:
b181d57f 2765
59723040
BF
2766[[fetch-fast-forwards]]
2767git fetch and fast-forwards
2768---------------------------
b181d57f 2769
6127c086 2770In the previous example, when updating an existing branch, "git fetch"
7a7d4ef6 2771checks to make sure that the most recent commit on the remote
b181d57f
BF
2772branch is a descendant of the most recent commit on your copy of the
2773branch before updating your copy of the branch to point at the new
a75d7b54 2774commit. Git calls this process a <<fast-forwards,fast-forward>>.
b181d57f 2775
a75d7b54 2776A fast-forward looks something like this:
b181d57f 2777
1dc71a91 2778................................................
b181d57f
BF
2779 o--o--o--o <-- old head of the branch
2780 \
2781 o--o--o <-- new head of the branch
1dc71a91 2782................................................
b181d57f
BF
2783
2784
2785In some cases it is possible that the new head will *not* actually be
2786a descendant of the old head. For example, the developer may have
2787realized she made a serious mistake, and decided to backtrack,
2788resulting in a situation like:
2789
1dc71a91 2790................................................
b181d57f
BF
2791 o--o--o--o--a--b <-- old head of the branch
2792 \
2793 o--o--o <-- new head of the branch
1dc71a91 2794................................................
b181d57f 2795
6127c086 2796In this case, "git fetch" will fail, and print out a warning.
b181d57f
BF
2797
2798In that case, you can still force git to update to the new head, as
2799described in the following section. However, note that in the
2800situation above this may mean losing the commits labeled "a" and "b",
2801unless you've already created a reference of your own pointing to
2802them.
2803
e34caace 2804[[forcing-fetch]]
6127c086 2805Forcing git fetch to do non-fast-forward updates
b181d57f
BF
2806------------------------------------------------
2807
2808If git fetch fails because the new head of a branch is not a
2809descendant of the old head, you may force the update with:
2810
2811-------------------------------------------------
2812$ git fetch git://example.com/proj.git +master:refs/remotes/example/master
2813-------------------------------------------------
2814
c64415e2
BF
2815Note the addition of the "+" sign. Alternatively, you can use the "-f"
2816flag to force updates of all the fetched branches, as in:
2817
2818-------------------------------------------------
2819$ git fetch -f origin
2820-------------------------------------------------
2821
2822Be aware that commits that the old version of example/master pointed at
2823may be lost, as we saw in the previous section.
b181d57f 2824
e34caace 2825[[remote-branch-configuration]]
29b9a66f
MM
2826Configuring remote-tracking branches
2827------------------------------------
b181d57f
BF
2828
2829We saw above that "origin" is just a shortcut to refer to the
79c96c57 2830repository that you originally cloned from. This information is
b181d57f 2831stored in git configuration variables, which you can see using
5162e697 2832linkgit:git-config[1]:
b181d57f
BF
2833
2834-------------------------------------------------
9d13bda3 2835$ git config -l
b181d57f
BF
2836core.repositoryformatversion=0
2837core.filemode=true
2838core.logallrefupdates=true
2839remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2840remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2841branch.master.remote=origin
2842branch.master.merge=refs/heads/master
2843-------------------------------------------------
2844
2845If there are other repositories that you also use frequently, you can
2846create similar configuration options to save typing; for example,
2847after
2848
2849-------------------------------------------------
9d13bda3 2850$ git config remote.example.url git://example.com/proj.git
b181d57f
BF
2851-------------------------------------------------
2852
2853then the following two commands will do the same thing:
2854
2855-------------------------------------------------
2856$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2857$ git fetch example master:refs/remotes/example/master
2858-------------------------------------------------
2859
2860Even better, if you add one more option:
2861
2862-------------------------------------------------
9d13bda3 2863$ git config remote.example.fetch master:refs/remotes/example/master
b181d57f
BF
2864-------------------------------------------------
2865
2866then the following commands will all do the same thing:
2867
2868-------------------------------------------------
52c80037
BF
2869$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2870$ git fetch example master:refs/remotes/example/master
b181d57f
BF
2871$ git fetch example
2872-------------------------------------------------
2873
2874You can also add a "+" to force the update each time:
2875
2876-------------------------------------------------
edfbbf7e 2877$ git config remote.example.fetch +master:refs/remotes/example/master
b181d57f
BF
2878-------------------------------------------------
2879
2880Don't do this unless you're sure you won't mind "git fetch" possibly
4f80b27d 2881throwing away commits on 'example/master'.
b181d57f
BF
2882
2883Also note that all of the above configuration can be performed by
2884directly editing the file .git/config instead of using
5162e697 2885linkgit:git-config[1].
b181d57f 2886
5162e697 2887See linkgit:git-config[1] for more details on the configuration
b181d57f 2888options mentioned above.
d19fbc3c 2889
d19fbc3c 2890
036f8199
BF
2891[[git-concepts]]
2892Git concepts
2893============
d19fbc3c 2894
036f8199
BF
2895Git is built on a small number of simple but powerful ideas. While it
2896is possible to get things done without understanding them, you will find
2897git much more intuitive if you do.
2898
2899We start with the most important, the <<def_object_database,object
2900database>> and the <<def_index,index>>.
b181d57f 2901
e34caace 2902[[the-object-database]]
b181d57f
BF
2903The Object Database
2904-------------------
2905
1bbf1c79
BF
2906
2907We already saw in <<understanding-commits>> that all commits are stored
2908under a 40-digit "object name". In fact, all the information needed to
2909represent the history of a project is stored in objects with such names.
a6e5ef7d
FC
2910In each case the name is calculated by taking the SHA-1 hash of the
2911contents of the object. The SHA-1 hash is a cryptographic hash function.
1bbf1c79
BF
2912What that means to us is that it is impossible to find two different
2913objects with the same name. This has a number of advantages; among
2914others:
2915
2916- Git can quickly determine whether two objects are identical or not,
2917 just by comparing names.
06ada152 2918- Since object names are computed the same way in every repository, the
1bbf1c79
BF
2919 same content stored in two repositories will always be stored under
2920 the same name.
2921- Git can detect errors when it reads an object, by checking that the
a6e5ef7d 2922 object's name is still the SHA-1 hash of its contents.
1bbf1c79
BF
2923
2924(See <<object-details>> for the details of the object formatting and
a6e5ef7d 2925SHA-1 calculation.)
1bbf1c79
BF
2926
2927There are four different types of objects: "blob", "tree", "commit", and
2928"tag".
2929
2930- A <<def_blob_object,"blob" object>> is used to store file data.
843c81dc 2931- A <<def_tree_object,"tree" object>> ties one or more
1bbf1c79
BF
2932 "blob" objects into a directory structure. In addition, a tree object
2933 can refer to other tree objects, thus creating a directory hierarchy.
2934- A <<def_commit_object,"commit" object>> ties such directory hierarchies
2ef8ac1b 2935 together into a <<def_DAG,directed acyclic graph>> of revisions--each
1bbf1c79
BF
2936 commit contains the object name of exactly one tree designating the
2937 directory hierarchy at the time of the commit. In addition, a commit
2938 refers to "parent" commit objects that describe the history of how we
2939 arrived at that directory hierarchy.
2940- A <<def_tag_object,"tag" object>> symbolically identifies and can be
2941 used to sign other objects. It contains the object name and type of
2942 another object, a symbolic name (of course!) and, optionally, a
2943 signature.
b181d57f 2944
b181d57f
BF
2945The object types in some more detail:
2946
513d419c
BF
2947[[commit-object]]
2948Commit Object
2949~~~~~~~~~~~~~
b181d57f 2950
1bbf1c79
BF
2951The "commit" object links a physical state of a tree with a description
2952of how we got there and why. Use the --pretty=raw option to
5162e697 2953linkgit:git-show[1] or linkgit:git-log[1] to examine your favorite
1bbf1c79
BF
2954commit:
2955
2956------------------------------------------------
2957$ git show -s --pretty=raw 2be7fcb476
2958commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4
2959tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf
2960parent 257a84d9d02e90447b149af58b271c19405edb6a
2961author Dave Watson <dwatson@mimvista.com> 1187576872 -0400
2962committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700
2963
2964 Fix misspelling of 'suppress' in docs
2965
2966 Signed-off-by: Junio C Hamano <gitster@pobox.com>
2967------------------------------------------------
2968
2969As you can see, a commit is defined by:
2970
a6e5ef7d 2971- a tree: The SHA-1 name of a tree object (as defined below), representing
1bbf1c79 2972 the contents of a directory at a certain point in time.
edfbbf7e 2973- parent(s): The SHA-1 name(s) of some number of commits which represent the
9e5d87d4 2974 immediately previous step(s) in the history of the project. The
1bbf1c79
BF
2975 example above has one parent; merge commits may have more than
2976 one. A commit with no parents is called a "root" commit, and
2977 represents the initial revision of a project. Each project must have
2978 at least one root. A project can also have multiple roots, though
2979 that isn't common (or necessarily a good idea).
2980- an author: The name of the person responsible for this change, together
2981 with its date.
2982- a committer: The name of the person who actually created the commit,
2983 with the date it was done. This may be different from the author, for
2984 example, if the author was someone who wrote a patch and emailed it
2985 to the person who used it to create the commit.
2986- a comment describing this commit.
2987
2988Note that a commit does not itself contain any information about what
2989actually changed; all changes are calculated by comparing the contents
2990of the tree referred to by this commit with the trees associated with
2991its parents. In particular, git does not attempt to record file renames
2992explicitly, though it can identify cases where the existence of the same
2993file data at changing paths suggests a rename. (See, for example, the
5162e697 2994-M option to linkgit:git-diff[1]).
1bbf1c79 2995
5162e697 2996A commit is usually created by linkgit:git-commit[1], which creates a
1bbf1c79
BF
2997commit whose parent is normally the current HEAD, and whose tree is
2998taken from the content currently stored in the index.
b181d57f 2999
e34caace 3000[[tree-object]]
b181d57f 3001Tree Object
971aa71f 3002~~~~~~~~~~~
b181d57f 3003
5162e697
DM
3004The ever-versatile linkgit:git-show[1] command can also be used to
3005examine tree objects, but linkgit:git-ls-tree[1] will give you more
1bbf1c79
BF
3006details:
3007
3008------------------------------------------------
3009$ git ls-tree fb3a8bdd0ce
3010100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore
3011100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap
3012100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING
3013040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation
3014100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN
3015100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL
3016100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile
3017100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README
3018...
3019------------------------------------------------
3020
3021As you can see, a tree object contains a list of entries, each with a
a6e5ef7d 3022mode, object type, SHA-1 name, and name, sorted by name. It represents
1bbf1c79
BF
3023the contents of a single directory tree.
3024
3025The object type may be a blob, representing the contents of a file, or
3026another tree, representing the contents of a subdirectory. Since trees
a6e5ef7d
FC
3027and blobs, like all other objects, are named by the SHA-1 hash of their
3028contents, two trees have the same SHA-1 name if and only if their
1bbf1c79
BF
3029contents (including, recursively, the contents of all subdirectories)
3030are identical. This allows git to quickly determine the differences
3031between two related tree objects, since it can ignore any entries with
3032identical object names.
3033
3034(Note: in the presence of submodules, trees may also have commits as
6dd14366 3035entries. See <<submodules>> for documentation.)
1bbf1c79
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3036
3037Note that the files all have mode 644 or 755: git actually only pays
3038attention to the executable bit.
b181d57f 3039
513d419c
BF
3040[[blob-object]]
3041Blob Object
3042~~~~~~~~~~~
b181d57f 3043
5162e697 3044You can use linkgit:git-show[1] to examine the contents of a blob; take,
1bbf1c79 3045for example, the blob in the entry for "COPYING" from the tree above:
b181d57f 3046
1bbf1c79
BF
3047------------------------------------------------
3048$ git show 6ff87c4664
3049
3050 Note that the only valid version of the GPL as far as this project
3051 is concerned is _this_ particular version of the license (ie v2, not
3052 v2.2 or v3.x or whatever), unless explicitly otherwise stated.
3053...
3054------------------------------------------------
b181d57f 3055
1bbf1c79
BF
3056A "blob" object is nothing but a binary blob of data. It doesn't refer
3057to anything else or have attributes of any kind.
3058
3059Since the blob is entirely defined by its data, if two files in a
3060directory tree (or in multiple different versions of the repository)
3061have the same contents, they will share the same blob object. The object
3062is totally independent of its location in the directory tree, and
3063renaming a file does not change the object that file is associated with.
3064
3065Note that any tree or blob object can be examined using
5162e697 3066linkgit:git-show[1] with the <revision>:<path> syntax. This can
1bbf1c79
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3067sometimes be useful for browsing the contents of a tree that is not
3068currently checked out.
b181d57f 3069
e34caace 3070[[trust]]
b181d57f 3071Trust
971aa71f 3072~~~~~
b181d57f 3073
a6e5ef7d 3074If you receive the SHA-1 name of a blob from one source, and its contents
1bbf1c79 3075from another (possibly untrusted) source, you can still trust that those
a6e5ef7d
FC
3076contents are correct as long as the SHA-1 name agrees. This is because
3077the SHA-1 is designed so that it is infeasible to find different contents
1bbf1c79 3078that produce the same hash.
b181d57f 3079
a6e5ef7d 3080Similarly, you need only trust the SHA-1 name of a top-level tree object
1bbf1c79 3081to trust the contents of the entire directory that it refers to, and if
a6e5ef7d 3082you receive the SHA-1 name of a commit from a trusted source, then you
1bbf1c79
BF
3083can easily verify the entire history of commits reachable through
3084parents of that commit, and all of those contents of the trees referred
3085to by those commits.
b181d57f
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3086
3087So to introduce some real trust in the system, the only thing you need
3088to do is to digitally sign just 'one' special note, which includes the
3089name of a top-level commit. Your digital signature shows others
3090that you trust that commit, and the immutability of the history of
3091commits tells others that they can trust the whole history.
3092
3093In other words, you can easily validate a whole archive by just
a6e5ef7d 3094sending out a single email that tells the people the name (SHA-1 hash)
b181d57f
BF
3095of the top commit, and digitally sign that email using something
3096like GPG/PGP.
3097
3098To assist in this, git also provides the tag object...
3099
e34caace 3100[[tag-object]]
b181d57f 3101Tag Object
971aa71f 3102~~~~~~~~~~
b181d57f 3103
1bbf1c79
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3104A tag object contains an object, object type, tag name, the name of the
3105person ("tagger") who created the tag, and a message, which may contain
843c81dc 3106a signature, as can be seen using linkgit:git-cat-file[1]:
b181d57f 3107
1bbf1c79
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3108------------------------------------------------
3109$ git cat-file tag v1.5.0
3110object 437b1b20df4b356c9342dac8d38849f24ef44f27
3111type commit
3112tag v1.5.0
3113tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000
3114
3115GIT 1.5.0
3116-----BEGIN PGP SIGNATURE-----
3117Version: GnuPG v1.4.6 (GNU/Linux)
3118
3119iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui
3120nLE/L9aUXdWeTFPron96DLA=
3121=2E+0
3122-----END PGP SIGNATURE-----
3123------------------------------------------------
b181d57f 3124
5162e697
DM
3125See the linkgit:git-tag[1] command to learn how to create and verify tag
3126objects. (Note that linkgit:git-tag[1] can also be used to create
1bbf1c79 3127"lightweight tags", which are not tag objects at all, but just simple
fc74ecc1 3128references whose names begin with "refs/tags/").
b181d57f 3129
09eff7b0
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3130[[pack-files]]
3131How git stores objects efficiently: pack files
3132~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3133
9644ffdd 3134Newly created objects are initially created in a file named after the
a6e5ef7d 3135object's SHA-1 hash (stored in .git/objects).
09eff7b0
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3136
3137Unfortunately this system becomes inefficient once a project has a
3138lot of objects. Try this on an old project:
3139
3140------------------------------------------------
3141$ git count-objects
31426930 objects, 47620 kilobytes
3143------------------------------------------------
3144
3145The first number is the number of objects which are kept in
3146individual files. The second is the amount of space taken up by
3147those "loose" objects.
3148
3149You can save space and make git faster by moving these loose objects in
3150to a "pack file", which stores a group of objects in an efficient
3151compressed format; the details of how pack files are formatted can be
3152found in link:technical/pack-format.txt[technical/pack-format.txt].
3153
3154To put the loose objects into a pack, just run git repack:
3155
3156------------------------------------------------
3157$ git repack
3158Generating pack...
3159Done counting 6020 objects.
3160Deltifying 6020 objects.
3161 100% (6020/6020) done
3162Writing 6020 objects.
3163 100% (6020/6020) done
3164Total 6020, written 6020 (delta 4070), reused 0 (delta 0)
3165Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.
3166------------------------------------------------
3167
3168You can then run
3169
3170------------------------------------------------
3171$ git prune
3172------------------------------------------------
3173
3174to remove any of the "loose" objects that are now contained in the
3175pack. This will also remove any unreferenced objects (which may be
6127c086 3176created when, for example, you use "git reset" to remove a commit).
09eff7b0
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3177You can verify that the loose objects are gone by looking at the
3178.git/objects directory or by running
3179
3180------------------------------------------------
3181$ git count-objects
31820 objects, 0 kilobytes
3183------------------------------------------------
3184
3185Although the object files are gone, any commands that refer to those
3186objects will work exactly as they did before.
3187
5162e697 3188The linkgit:git-gc[1] command performs packing, pruning, and more for
09eff7b0
BF
3189you, so is normally the only high-level command you need.
3190
3191[[dangling-objects]]
3192Dangling objects
3193~~~~~~~~~~~~~~~~
3194
5162e697 3195The linkgit:git-fsck[1] command will sometimes complain about dangling
09eff7b0
BF
3196objects. They are not a problem.
3197
3198The most common cause of dangling objects is that you've rebased a
3199branch, or you have pulled from somebody else who rebased a branch--see
3200<<cleaning-up-history>>. In that case, the old head of the original
3201branch still exists, as does everything it pointed to. The branch
3202pointer itself just doesn't, since you replaced it with another one.
3203
3204There are also other situations that cause dangling objects. For
6127c086 3205example, a "dangling blob" may arise because you did a "git add" of a
09eff7b0
BF
3206file, but then, before you actually committed it and made it part of the
3207bigger picture, you changed something else in that file and committed
2ef8ac1b 3208that *updated* thing--the old state that you added originally ends up
09eff7b0
BF
3209not being pointed to by any commit or tree, so it's now a dangling blob
3210object.
3211
3212Similarly, when the "recursive" merge strategy runs, and finds that
3213there are criss-cross merges and thus more than one merge base (which is
3214fairly unusual, but it does happen), it will generate one temporary
3215midway tree (or possibly even more, if you had lots of criss-crossing
3216merges and more than two merge bases) as a temporary internal merge
3217base, and again, those are real objects, but the end result will not end
3218up pointing to them, so they end up "dangling" in your repository.
3219
3220Generally, dangling objects aren't anything to worry about. They can
3221even be very useful: if you screw something up, the dangling objects can
3222be how you recover your old tree (say, you did a rebase, and realized
2ef8ac1b 3223that you really didn't want to--you can look at what dangling objects
09eff7b0
BF
3224you have, and decide to reset your head to some old dangling state).
3225
3226For commits, you can just use:
3227
3228------------------------------------------------
3229$ gitk <dangling-commit-sha-goes-here> --not --all
3230------------------------------------------------
3231
3232This asks for all the history reachable from the given commit but not
3233from any branch, tag, or other reference. If you decide it's something
3234you want, you can always create a new reference to it, e.g.,
3235
3236------------------------------------------------
3237$ git branch recovered-branch <dangling-commit-sha-goes-here>
3238------------------------------------------------
3239
3240For blobs and trees, you can't do the same, but you can still examine
3241them. You can just do
3242
3243------------------------------------------------
3244$ git show <dangling-blob/tree-sha-goes-here>
3245------------------------------------------------
3246
3247to show what the contents of the blob were (or, for a tree, basically
3248what the "ls" for that directory was), and that may give you some idea
3249of what the operation was that left that dangling object.
3250
3251Usually, dangling blobs and trees aren't very interesting. They're
3252almost always the result of either being a half-way mergebase (the blob
3253will often even have the conflict markers from a merge in it, if you
3254have had conflicting merges that you fixed up by hand), or simply
6127c086 3255because you interrupted a "git fetch" with ^C or something like that,
09eff7b0
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3256leaving _some_ of the new objects in the object database, but just
3257dangling and useless.
3258
3259Anyway, once you are sure that you're not interested in any dangling
3260state, you can just prune all unreachable objects:
3261
3262------------------------------------------------
3263$ git prune
3264------------------------------------------------
3265
3266and they'll be gone. But you should only run "git prune" on a quiescent
2ef8ac1b 3267repository--it's kind of like doing a filesystem fsck recovery: you
09eff7b0
BF
3268don't want to do that while the filesystem is mounted.
3269
6127c086
FC
3270(The same is true of "git fsck" itself, btw, but since
3271`git fsck` never actually *changes* the repository, it just reports
3272on what it found, `git fsck` itself is never 'dangerous' to run.
09eff7b0
BF
3273Running it while somebody is actually changing the repository can cause
3274confusing and scary messages, but it won't actually do anything bad. In
3275contrast, running "git prune" while somebody is actively changing the
3276repository is a *BAD* idea).
b181d57f 3277
1cdade2c
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3278[[recovering-from-repository-corruption]]
3279Recovering from repository corruption
3280~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3281
3282By design, git treats data trusted to it with caution. However, even in
3283the absence of bugs in git itself, it is still possible that hardware or
3284operating system errors could corrupt data.
3285
3286The first defense against such problems is backups. You can back up a
3287git directory using clone, or just using cp, tar, or any other backup
3288mechanism.
3289
3290As a last resort, you can search for the corrupted objects and attempt
3291to replace them by hand. Back up your repository before attempting this
3292in case you corrupt things even more in the process.
3293
3294We'll assume that the problem is a single missing or corrupted blob,