user-manual.txt: explain better the remote(-tracking) branch terms
[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 cannot check out these remote-tracking branches, but you can
371examine them on a branch of your own, just as you would a tag:
372
373------------------------------------------------
374$ git checkout -b my-todo-copy origin/todo
375------------------------------------------------
376
377Note that the name "origin" is just the name that git uses by default
378to refer to the repository that you cloned from.
379
380[[how-git-stores-references]]
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381Naming branches, tags, and other references
382-------------------------------------------
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383
384Branches, remote-tracking branches, and tags are all references to
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385commits. All references are named with a slash-separated path name
386starting with "refs"; the names we've been using so far are actually
387shorthand:
d19fbc3c 388
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389 - The branch "test" is short for "refs/heads/test".
390 - The tag "v2.6.18" is short for "refs/tags/v2.6.18".
391 - "origin/master" is short for "refs/remotes/origin/master".
d19fbc3c 392
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393The full name is occasionally useful if, for example, there ever
394exists a tag and a branch with the same name.
d19fbc3c 395
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396(Newly created refs are actually stored in the .git/refs directory,
397under the path given by their name. However, for efficiency reasons
398they may also be packed together in a single file; see
5162e697 399linkgit:git-pack-refs[1]).
fc74ecc1 400
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401As another useful shortcut, the "HEAD" of a repository can be referred
402to just using the name of that repository. So, for example, "origin"
403is usually a shortcut for the HEAD branch in the repository "origin".
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404
405For the complete list of paths which git checks for references, and
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406the order it uses to decide which to choose when there are multiple
407references with the same shorthand name, see the "SPECIFYING
9d83e382 408REVISIONS" section of linkgit:gitrevisions[7].
d19fbc3c 409
aa971cb9 410[[Updating-a-repository-With-git-fetch]]
6127c086 411Updating a repository with git fetch
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412------------------------------------
413
414Eventually the developer cloned from will do additional work in her
415repository, creating new commits and advancing the branches to point
416at the new commits.
417
418The command "git fetch", with no arguments, will update all of the
419remote-tracking branches to the latest version found in her
420repository. It will not touch any of your own branches--not even the
421"master" branch that was created for you on clone.
422
e34caace 423[[fetching-branches]]
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424Fetching branches from other repositories
425-----------------------------------------
426
427You can also track branches from repositories other than the one you
5162e697 428cloned from, using linkgit:git-remote[1]:
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429
430-------------------------------------------------
431$ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git
04483524 432$ git fetch linux-nfs
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433* refs/remotes/linux-nfs/master: storing branch 'master' ...
434 commit: bf81b46
435-------------------------------------------------
436
437New remote-tracking branches will be stored under the shorthand name
6127c086 438that you gave "git remote add", in this case linux-nfs:
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439
440-------------------------------------------------
441$ git branch -r
442linux-nfs/master
443origin/master
444-------------------------------------------------
445
8b3f3f84 446If you run "git fetch <remote>" later, the remote-tracking branches for the
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447named <remote> will be updated.
448
449If you examine the file .git/config, you will see that git has added
450a new stanza:
451
452-------------------------------------------------
453$ cat .git/config
454...
455[remote "linux-nfs"]
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456 url = git://linux-nfs.org/pub/nfs-2.6.git
457 fetch = +refs/heads/*:refs/remotes/linux-nfs/*
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458...
459-------------------------------------------------
460
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461This is what causes git to track the remote's branches; you may modify
462or delete these configuration options by editing .git/config with a
463text editor. (See the "CONFIGURATION FILE" section of
5162e697 464linkgit:git-config[1] for details.)
d5cd5de4 465
e34caace 466[[exploring-git-history]]
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467Exploring git history
468=====================
469
470Git is best thought of as a tool for storing the history of a
471collection of files. It does this by storing compressed snapshots of
1130845b 472the contents of a file hierarchy, together with "commits" which show
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473the relationships between these snapshots.
474
475Git provides extremely flexible and fast tools for exploring the
476history of a project.
477
aacd404e 478We start with one specialized tool that is useful for finding the
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479commit that introduced a bug into a project.
480
e34caace 481[[using-bisect]]
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482How to use bisect to find a regression
483--------------------------------------
484
485Suppose version 2.6.18 of your project worked, but the version at
486"master" crashes. Sometimes the best way to find the cause of such a
487regression is to perform a brute-force search through the project's
488history to find the particular commit that caused the problem. The
5162e697 489linkgit:git-bisect[1] command can help you do this:
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490
491-------------------------------------------------
492$ git bisect start
493$ git bisect good v2.6.18
494$ git bisect bad master
495Bisecting: 3537 revisions left to test after this
496[65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]
497-------------------------------------------------
498
499If you run "git branch" at this point, you'll see that git has
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500temporarily moved you in "(no branch)". HEAD is now detached from any
501branch and points directly to a commit (with commit id 65934...) that
502is reachable from "master" but not from v2.6.18. Compile and test it,
503and see whether it crashes. Assume it does crash. Then:
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504
505-------------------------------------------------
506$ git bisect bad
507Bisecting: 1769 revisions left to test after this
508[7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings
509-------------------------------------------------
510
511checks out an older version. Continue like this, telling git at each
512stage whether the version it gives you is good or bad, and notice
513that the number of revisions left to test is cut approximately in
514half each time.
515
516After about 13 tests (in this case), it will output the commit id of
517the guilty commit. You can then examine the commit with
5162e697 518linkgit:git-show[1], find out who wrote it, and mail them your bug
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519report with the commit id. Finally, run
520
521-------------------------------------------------
522$ git bisect reset
523-------------------------------------------------
524
0e25790f 525to return you to the branch you were on before.
d19fbc3c 526
6127c086 527Note that the version which `git bisect` checks out for you at each
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528point is just a suggestion, and you're free to try a different
529version if you think it would be a good idea. For example,
530occasionally you may land on a commit that broke something unrelated;
531run
532
533-------------------------------------------------
04483524 534$ git bisect visualize
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535-------------------------------------------------
536
537which will run gitk and label the commit it chose with a marker that
843c81dc 538says "bisect". Choose a safe-looking commit nearby, note its commit
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539id, and check it out with:
540
541-------------------------------------------------
542$ git reset --hard fb47ddb2db...
543-------------------------------------------------
544
545then test, run "bisect good" or "bisect bad" as appropriate, and
546continue.
547
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548Instead of "git bisect visualize" and then "git reset --hard
549fb47ddb2db...", you might just want to tell git that you want to skip
550the current commit:
551
552-------------------------------------------------
553$ git bisect skip
554-------------------------------------------------
555
556In this case, though, git may not eventually be able to tell the first
a0178ae2 557bad one between some first skipped commits and a later bad commit.
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558
559There are also ways to automate the bisecting process if you have a
560test script that can tell a good from a bad commit. See
561linkgit:git-bisect[1] for more information about this and other "git
562bisect" features.
563
e34caace 564[[naming-commits]]
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565Naming commits
566--------------
567
568We have seen several ways of naming commits already:
569
d55ae921 570 - 40-hexdigit object name
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571 - branch name: refers to the commit at the head of the given
572 branch
573 - tag name: refers to the commit pointed to by the given tag
574 (we've seen branches and tags are special cases of
575 <<how-git-stores-references,references>>).
576 - HEAD: refers to the head of the current branch
577
eb6ae7f4 578There are many more; see the "SPECIFYING REVISIONS" section of the
9d83e382 579linkgit:gitrevisions[7] man page for the complete list of ways to
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580name revisions. Some examples:
581
582-------------------------------------------------
d55ae921 583$ git show fb47ddb2 # the first few characters of the object name
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584 # are usually enough to specify it uniquely
585$ git show HEAD^ # the parent of the HEAD commit
586$ git show HEAD^^ # the grandparent
587$ git show HEAD~4 # the great-great-grandparent
588-------------------------------------------------
589
590Recall that merge commits may have more than one parent; by default,
591^ and ~ follow the first parent listed in the commit, but you can
592also choose:
593
594-------------------------------------------------
595$ git show HEAD^1 # show the first parent of HEAD
596$ git show HEAD^2 # show the second parent of HEAD
597-------------------------------------------------
598
599In addition to HEAD, there are several other special names for
600commits:
601
602Merges (to be discussed later), as well as operations such as
6127c086 603`git reset`, which change the currently checked-out commit, generally
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604set ORIG_HEAD to the value HEAD had before the current operation.
605
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606The `git fetch` operation always stores the head of the last fetched
607branch in FETCH_HEAD. For example, if you run `git fetch` without
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608specifying a local branch as the target of the operation
609
610-------------------------------------------------
611$ git fetch git://example.com/proj.git theirbranch
612-------------------------------------------------
613
614the fetched commits will still be available from FETCH_HEAD.
615
616When we discuss merges we'll also see the special name MERGE_HEAD,
617which refers to the other branch that we're merging in to the current
618branch.
619
5162e697 620The linkgit:git-rev-parse[1] command is a low-level command that is
d55ae921
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621occasionally useful for translating some name for a commit to the object
622name for that commit:
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623
624-------------------------------------------------
625$ git rev-parse origin
626e05db0fd4f31dde7005f075a84f96b360d05984b
627-------------------------------------------------
628
e34caace 629[[creating-tags]]
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630Creating tags
631-------------
632
633We can also create a tag to refer to a particular commit; after
634running
635
636-------------------------------------------------
04483524 637$ git tag stable-1 1b2e1d63ff
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638-------------------------------------------------
639
640You can use stable-1 to refer to the commit 1b2e1d63ff.
641
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642This creates a "lightweight" tag. If you would also like to include a
643comment with the tag, and possibly sign it cryptographically, then you
5162e697 644should create a tag object instead; see the linkgit:git-tag[1] man page
c64415e2 645for details.
d19fbc3c 646
e34caace 647[[browsing-revisions]]
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648Browsing revisions
649------------------
650
5162e697 651The linkgit:git-log[1] command can show lists of commits. On its
d19fbc3c
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652own, it shows all commits reachable from the parent commit; but you
653can also make more specific requests:
654
655-------------------------------------------------
656$ git log v2.5.. # commits since (not reachable from) v2.5
657$ git log test..master # commits reachable from master but not test
658$ git log master..test # ...reachable from test but not master
659$ git log master...test # ...reachable from either test or master,
660 # but not both
661$ git log --since="2 weeks ago" # commits from the last 2 weeks
662$ git log Makefile # commits which modify Makefile
663$ git log fs/ # ... which modify any file under fs/
664$ git log -S'foo()' # commits which add or remove any file data
665 # matching the string 'foo()'
666-------------------------------------------------
667
668And of course you can combine all of these; the following finds
669commits since v2.5 which touch the Makefile or any file under fs:
670
671-------------------------------------------------
672$ git log v2.5.. Makefile fs/
673-------------------------------------------------
674
675You can also ask git log to show patches:
676
677-------------------------------------------------
678$ git log -p
679-------------------------------------------------
680
5162e697 681See the "--pretty" option in the linkgit:git-log[1] man page for more
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682display options.
683
684Note that git log starts with the most recent commit and works
685backwards through the parents; however, since git history can contain
3dff5379 686multiple independent lines of development, the particular order that
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687commits are listed in may be somewhat arbitrary.
688
e34caace 689[[generating-diffs]]
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690Generating diffs
691----------------
692
693You can generate diffs between any two versions using
5162e697 694linkgit:git-diff[1]:
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695
696-------------------------------------------------
697$ git diff master..test
698-------------------------------------------------
699
5b98d9bc
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700That will produce the diff between the tips of the two branches. If
701you'd prefer to find the diff from their common ancestor to test, you
702can use three dots instead of two:
703
704-------------------------------------------------
705$ git diff master...test
706-------------------------------------------------
707
708Sometimes what you want instead is a set of patches; for this you can
5162e697 709use linkgit:git-format-patch[1]:
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710
711-------------------------------------------------
712$ git format-patch master..test
713-------------------------------------------------
714
715will generate a file with a patch for each commit reachable from test
5b98d9bc 716but not from master.
d19fbc3c 717
e34caace 718[[viewing-old-file-versions]]
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719Viewing old file versions
720-------------------------
721
722You can always view an old version of a file by just checking out the
723correct revision first. But sometimes it is more convenient to be
724able to view an old version of a single file without checking
725anything out; this command does that:
726
727-------------------------------------------------
728$ git show v2.5:fs/locks.c
729-------------------------------------------------
730
731Before the colon may be anything that names a commit, and after it
732may be any path to a file tracked by git.
733
e34caace 734[[history-examples]]
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735Examples
736--------
737
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738[[counting-commits-on-a-branch]]
739Counting the number of commits on a branch
740~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
741
742Suppose you want to know how many commits you've made on "mybranch"
743since it diverged from "origin":
744
745-------------------------------------------------
746$ git log --pretty=oneline origin..mybranch | wc -l
747-------------------------------------------------
748
749Alternatively, you may often see this sort of thing done with the
a6e5ef7d 750lower-level command linkgit:git-rev-list[1], which just lists the SHA-1's
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751of all the given commits:
752
753-------------------------------------------------
754$ git rev-list origin..mybranch | wc -l
755-------------------------------------------------
756
e34caace 757[[checking-for-equal-branches]]
aec053bb 758Check whether two branches point at the same history
2f99710c 759~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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760
761Suppose you want to check whether two branches point at the same point
762in history.
763
764-------------------------------------------------
765$ git diff origin..master
766-------------------------------------------------
767
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768will tell you whether the contents of the project are the same at the
769two branches; in theory, however, it's possible that the same project
770contents could have been arrived at by two different historical
d55ae921 771routes. You could compare the object names:
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772
773-------------------------------------------------
774$ git rev-list origin
775e05db0fd4f31dde7005f075a84f96b360d05984b
776$ git rev-list master
777e05db0fd4f31dde7005f075a84f96b360d05984b
778-------------------------------------------------
779
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780Or you could recall that the ... operator selects all commits
781contained reachable from either one reference or the other but not
782both: so
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783
784-------------------------------------------------
785$ git log origin...master
786-------------------------------------------------
787
788will return no commits when the two branches are equal.
789
e34caace 790[[finding-tagged-descendants]]
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791Find first tagged version including a given fix
792~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
aec053bb 793
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794Suppose you know that the commit e05db0fd fixed a certain problem.
795You'd like to find the earliest tagged release that contains that
796fix.
797
798Of course, there may be more than one answer--if the history branched
799after commit e05db0fd, then there could be multiple "earliest" tagged
800releases.
801
802You could just visually inspect the commits since e05db0fd:
803
804-------------------------------------------------
805$ gitk e05db0fd..
806-------------------------------------------------
807
5162e697 808Or you can use linkgit:git-name-rev[1], which will give the commit a
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809name based on any tag it finds pointing to one of the commit's
810descendants:
811
812-------------------------------------------------
04483524 813$ git name-rev --tags e05db0fd
b181d57f
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814e05db0fd tags/v1.5.0-rc1^0~23
815-------------------------------------------------
816
5162e697 817The linkgit:git-describe[1] command does the opposite, naming the
b181d57f
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818revision using a tag on which the given commit is based:
819
820-------------------------------------------------
821$ git describe e05db0fd
04483524 822v1.5.0-rc0-260-ge05db0f
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823-------------------------------------------------
824
825but that may sometimes help you guess which tags might come after the
826given commit.
827
828If you just want to verify whether a given tagged version contains a
5162e697 829given commit, you could use linkgit:git-merge-base[1]:
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830
831-------------------------------------------------
832$ git merge-base e05db0fd v1.5.0-rc1
833e05db0fd4f31dde7005f075a84f96b360d05984b
834-------------------------------------------------
835
836The merge-base command finds a common ancestor of the given commits,
837and always returns one or the other in the case where one is a
838descendant of the other; so the above output shows that e05db0fd
839actually is an ancestor of v1.5.0-rc1.
840
841Alternatively, note that
842
843-------------------------------------------------
4a7979ca 844$ git log v1.5.0-rc1..e05db0fd
b181d57f
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845-------------------------------------------------
846
4a7979ca 847will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
b181d57f 848because it outputs only commits that are not reachable from v1.5.0-rc1.
aec053bb 849
5162e697 850As yet another alternative, the linkgit:git-show-branch[1] command lists
4a7979ca
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851the commits reachable from its arguments with a display on the left-hand
852side that indicates which arguments that commit is reachable from. So,
853you can run something like
854
855-------------------------------------------------
856$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2
857! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
858available
859 ! [v1.5.0-rc0] GIT v1.5.0 preview
860 ! [v1.5.0-rc1] GIT v1.5.0-rc1
861 ! [v1.5.0-rc2] GIT v1.5.0-rc2
862...
863-------------------------------------------------
864
865then search for a line that looks like
866
867-------------------------------------------------
868+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
869available
870-------------------------------------------------
871
872Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and
873from v1.5.0-rc2, but not from v1.5.0-rc0.
874
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875[[showing-commits-unique-to-a-branch]]
876Showing commits unique to a given branch
877~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4a7979ca 878
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879Suppose you would like to see all the commits reachable from the branch
880head named "master" but not from any other head in your repository.
d19fbc3c 881
629d9f78 882We can list all the heads in this repository with
5162e697 883linkgit:git-show-ref[1]:
d19fbc3c 884
629d9f78
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885-------------------------------------------------
886$ git show-ref --heads
887bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial
888db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint
889a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master
89024dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2
8911e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes
892-------------------------------------------------
d19fbc3c 893
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894We can get just the branch-head names, and remove "master", with
895the help of the standard utilities cut and grep:
896
897-------------------------------------------------
898$ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master'
899refs/heads/core-tutorial
900refs/heads/maint
901refs/heads/tutorial-2
902refs/heads/tutorial-fixes
903-------------------------------------------------
904
905And then we can ask to see all the commits reachable from master
906but not from these other heads:
907
908-------------------------------------------------
909$ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |
910 grep -v '^refs/heads/master' )
911-------------------------------------------------
912
913Obviously, endless variations are possible; for example, to see all
914commits reachable from some head but not from any tag in the repository:
915
916-------------------------------------------------
c78974f7 917$ gitk $( git show-ref --heads ) --not $( git show-ref --tags )
629d9f78
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918-------------------------------------------------
919
9d83e382 920(See linkgit:gitrevisions[7] for explanations of commit-selecting
629d9f78
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921syntax such as `--not`.)
922
82c8bf28
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923[[making-a-release]]
924Creating a changelog and tarball for a software release
925~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
926
5162e697 927The linkgit:git-archive[1] command can create a tar or zip archive from
82c8bf28
BF
928any version of a project; for example:
929
930-------------------------------------------------
931$ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz
932-------------------------------------------------
933
934will use HEAD to produce a tar archive in which each filename is
ccd71866 935preceded by "project/".
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BF
936
937If you're releasing a new version of a software project, you may want
938to simultaneously make a changelog to include in the release
939announcement.
940
941Linus Torvalds, for example, makes new kernel releases by tagging them,
942then running:
943
944-------------------------------------------------
945$ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7
946-------------------------------------------------
947
948where release-script is a shell script that looks like:
949
950-------------------------------------------------
951#!/bin/sh
952stable="$1"
953last="$2"
954new="$3"
955echo "# git tag v$new"
956echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"
957echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"
958echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"
959echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"
960echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"
961-------------------------------------------------
962
963and then he just cut-and-pastes the output commands after verifying that
964they look OK.
4a7979ca 965
e1ba4c32 966[[Finding-commits-With-given-Content]]
187b0d80 967Finding commits referencing a file with given content
d5821de2 968~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
187b0d80
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969
970Somebody hands you a copy of a file, and asks which commits modified a
971file such that it contained the given content either before or after the
972commit. You can find out with this:
973
974-------------------------------------------------
477ff5b7 975$ git log --raw --abbrev=40 --pretty=oneline |
187b0d80
BF
976 grep -B 1 `git hash-object filename`
977-------------------------------------------------
978
979Figuring out why this works is left as an exercise to the (advanced)
5162e697
DM
980student. The linkgit:git-log[1], linkgit:git-diff-tree[1], and
981linkgit:git-hash-object[1] man pages may prove helpful.
187b0d80 982
aa971cb9 983[[Developing-With-git]]
d19fbc3c
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984Developing with git
985===================
986
e34caace 987[[telling-git-your-name]]
d19fbc3c
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988Telling git your name
989---------------------
990
991Before creating any commits, you should introduce yourself to git. The
58c19d1f
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992easiest way to do so is to make sure the following lines appear in a
993file named .gitconfig in your home directory:
d19fbc3c
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994
995------------------------------------------------
d19fbc3c
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996[user]
997 name = Your Name Comes Here
998 email = you@yourdomain.example.com
d19fbc3c
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999------------------------------------------------
1000
5162e697 1001(See the "CONFIGURATION FILE" section of linkgit:git-config[1] for
fc90c536
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1002details on the configuration file.)
1003
d19fbc3c 1004
e34caace 1005[[creating-a-new-repository]]
d19fbc3c
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1006Creating a new repository
1007-------------------------
1008
1009Creating a new repository from scratch is very easy:
1010
1011-------------------------------------------------
1012$ mkdir project
1013$ cd project
f1d2b477 1014$ git init
d19fbc3c
BF
1015-------------------------------------------------
1016
1017If you have some initial content (say, a tarball):
1018
1019-------------------------------------------------
0ddd93b2 1020$ tar xzvf project.tar.gz
d19fbc3c 1021$ cd project
f1d2b477 1022$ git init
d19fbc3c
BF
1023$ git add . # include everything below ./ in the first commit:
1024$ git commit
1025-------------------------------------------------
1026
1027[[how-to-make-a-commit]]
ae25c67a 1028How to make a commit
d19fbc3c
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1029--------------------
1030
1031Creating a new commit takes three steps:
1032
1033 1. Making some changes to the working directory using your
1034 favorite editor.
1035 2. Telling git about your changes.
1036 3. Creating the commit using the content you told git about
1037 in step 2.
1038
1039In practice, you can interleave and repeat steps 1 and 2 as many
1040times as you want: in order to keep track of what you want committed
1041at step 3, git maintains a snapshot of the tree's contents in a
1042special staging area called "the index."
1043
01997b4a
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1044At the beginning, the content of the index will be identical to
1045that of the HEAD. The command "git diff --cached", which shows
1046the difference between the HEAD and the index, should therefore
1047produce no output at that point.
eb6ae7f4 1048
d19fbc3c
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1049Modifying the index is easy:
1050
1051To update the index with the new contents of a modified file, use
1052
1053-------------------------------------------------
1054$ git add path/to/file
1055-------------------------------------------------
1056
1057To add the contents of a new file to the index, use
1058
1059-------------------------------------------------
1060$ git add path/to/file
1061-------------------------------------------------
1062
eb6ae7f4 1063To remove a file from the index and from the working tree,
d19fbc3c
BF
1064
1065-------------------------------------------------
1066$ git rm path/to/file
1067-------------------------------------------------
1068
1069After each step you can verify that
1070
1071-------------------------------------------------
1072$ git diff --cached
1073-------------------------------------------------
1074
1075always shows the difference between the HEAD and the index file--this
1076is what you'd commit if you created the commit now--and that
1077
1078-------------------------------------------------
1079$ git diff
1080-------------------------------------------------
1081
1082shows the difference between the working tree and the index file.
1083
6127c086 1084Note that "git add" always adds just the current contents of a file
d19fbc3c 1085to the index; further changes to the same file will be ignored unless
6127c086 1086you run `git add` on the file again.
d19fbc3c
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1087
1088When you're ready, just run
1089
1090-------------------------------------------------
1091$ git commit
1092-------------------------------------------------
1093
1094and git will prompt you for a commit message and then create the new
3dff5379 1095commit. Check to make sure it looks like what you expected with
d19fbc3c
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1096
1097-------------------------------------------------
1098$ git show
1099-------------------------------------------------
1100
1101As a special shortcut,
a6080a0a 1102
d19fbc3c
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1103-------------------------------------------------
1104$ git commit -a
1105-------------------------------------------------
1106
1107will update the index with any files that you've modified or removed
1108and create a commit, all in one step.
1109
1110A number of commands are useful for keeping track of what you're
1111about to commit:
1112
1113-------------------------------------------------
1114$ git diff --cached # difference between HEAD and the index; what
1130845b 1115 # would be committed if you ran "commit" now.
d19fbc3c
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1116$ git diff # difference between the index file and your
1117 # working directory; changes that would not
1118 # be included if you ran "commit" now.
c64415e2
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1119$ git diff HEAD # difference between HEAD and working tree; what
1120 # would be committed if you ran "commit -a" now.
d19fbc3c
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1121$ git status # a brief per-file summary of the above.
1122-------------------------------------------------
1123
5162e697 1124You can also use linkgit:git-gui[1] to create commits, view changes in
407c0c87
BF
1125the index and the working tree files, and individually select diff hunks
1126for inclusion in the index (by right-clicking on the diff hunk and
1127choosing "Stage Hunk For Commit").
1128
e34caace 1129[[creating-good-commit-messages]]
ae25c67a 1130Creating good commit messages
d19fbc3c
BF
1131-----------------------------
1132
1133Though not required, it's a good idea to begin the commit message
1134with a single short (less than 50 character) line summarizing the
1135change, followed by a blank line and then a more thorough
1136description. Tools that turn commits into email, for example, use
1137the first line on the Subject line and the rest of the commit in the
1138body.
1139
2dc53617
JH
1140[[ignoring-files]]
1141Ignoring files
1142--------------
1143
1144A project will often generate files that you do 'not' want to track with git.
1145This typically includes files generated by a build process or temporary
1146backup files made by your editor. Of course, 'not' tracking files with git
6127c086 1147is just a matter of 'not' calling `git add` on them. But it quickly becomes
2dc53617 1148annoying to have these untracked files lying around; e.g. they make
dcb11263
CJ
1149`git add .` practically useless, and they keep showing up in the output of
1150`git status`.
2dc53617 1151
464a8a7a
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1152You can tell git to ignore certain files by creating a file called .gitignore
1153in the top level of your working directory, with contents such as:
2dc53617
JH
1154
1155-------------------------------------------------
1156# Lines starting with '#' are considered comments.
464a8a7a 1157# Ignore any file named foo.txt.
2dc53617
JH
1158foo.txt
1159# Ignore (generated) html files,
1160*.html
1161# except foo.html which is maintained by hand.
1162!foo.html
1163# Ignore objects and archives.
1164*.[oa]
1165-------------------------------------------------
1166
5162e697 1167See linkgit:gitignore[5] for a detailed explanation of the syntax. You can
464a8a7a
BF
1168also place .gitignore files in other directories in your working tree, and they
1169will apply to those directories and their subdirectories. The `.gitignore`
1170files can be added to your repository like any other files (just run `git add
1171.gitignore` and `git commit`, as usual), which is convenient when the exclude
1172patterns (such as patterns matching build output files) would also make sense
1173for other users who clone your repository.
1174
1175If you wish the exclude patterns to affect only certain repositories
1176(instead of every repository for a given project), you may instead put
1177them in a file in your repository named .git/info/exclude, or in any file
1178specified by the `core.excludesfile` configuration variable. Some git
1179commands can also take exclude patterns directly on the command line.
5162e697 1180See linkgit:gitignore[5] for the details.
2dc53617 1181
e34caace 1182[[how-to-merge]]
ae25c67a 1183How to merge
d19fbc3c
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1184------------
1185
1186You can rejoin two diverging branches of development using
5162e697 1187linkgit:git-merge[1]:
d19fbc3c
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1188
1189-------------------------------------------------
1190$ git merge branchname
1191-------------------------------------------------
1192
1193merges the development in the branch "branchname" into the current
e63ec003
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1194branch.
1195
1196A merge is made by combining the changes made in "branchname" and the
1197changes made up to the latest commit in your current branch since
1198their histories forked. The work tree is overwritten by the result of
1199the merge when this combining is done cleanly, or overwritten by a
1200half-merged results when this combining results in conflicts.
1201Therefore, if you have uncommitted changes touching the same files as
1202the ones impacted by the merge, Git will refuse to proceed. Most of
1203the time, you will want to commit your changes before you can merge,
1204and if you don't, then linkgit:git-stash[1] can take these changes
1205away while you're doing the merge, and reapply them afterwards.
1206
6a5d0b0a 1207If the changes are independent enough, Git will automatically complete
e63ec003
MM
1208the merge and commit the result (or reuse an existing commit in case
1209of <<fast-forwards,fast-forward>>, see below). On the other hand,
1210if there are conflicts--for example, if the same file is
d19fbc3c
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1211modified in two different ways in the remote branch and the local
1212branch--then you are warned; the output may look something like this:
1213
1214-------------------------------------------------
fabbd8f6
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1215$ git merge next
1216 100% (4/4) done
1217Auto-merged file.txt
d19fbc3c
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1218CONFLICT (content): Merge conflict in file.txt
1219Automatic merge failed; fix conflicts and then commit the result.
1220-------------------------------------------------
1221
1222Conflict markers are left in the problematic files, and after
1223you resolve the conflicts manually, you can update the index
1224with the contents and run git commit, as you normally would when
1225creating a new file.
1226
1227If you examine the resulting commit using gitk, you will see that it
1228has two parents, one pointing to the top of the current branch, and
1229one to the top of the other branch.
1230
d19fbc3c
BF
1231[[resolving-a-merge]]
1232Resolving a merge
1233-----------------
1234
1235When a merge isn't resolved automatically, git leaves the index and
1236the working tree in a special state that gives you all the
1237information you need to help resolve the merge.
1238
1239Files with conflicts are marked specially in the index, so until you
5162e697 1240resolve the problem and update the index, linkgit:git-commit[1] will
ef561ac7 1241fail:
d19fbc3c
BF
1242
1243-------------------------------------------------
1244$ git commit
1245file.txt: needs merge
1246-------------------------------------------------
1247
5162e697 1248Also, linkgit:git-status[1] will list those files as "unmerged", and the
ef561ac7
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1249files with conflicts will have conflict markers added, like this:
1250
1251-------------------------------------------------
1252<<<<<<< HEAD:file.txt
1253Hello world
1254=======
1255Goodbye
1256>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1257-------------------------------------------------
1258
1259All you need to do is edit the files to resolve the conflicts, and then
1260
1261-------------------------------------------------
1262$ git add file.txt
1263$ git commit
1264-------------------------------------------------
1265
1266Note that the commit message will already be filled in for you with
1267some information about the merge. Normally you can just use this
1268default message unchanged, but you may add additional commentary of
1269your own if desired.
1270
1271The above is all you need to know to resolve a simple merge. But git
1272also provides more information to help resolve conflicts:
1273
e34caace 1274[[conflict-resolution]]
ef561ac7
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1275Getting conflict-resolution help during a merge
1276~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
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1277
1278All of the changes that git was able to merge automatically are
5162e697 1279already added to the index file, so linkgit:git-diff[1] shows only
ef561ac7 1280the conflicts. It uses an unusual syntax:
d19fbc3c
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1281
1282-------------------------------------------------
1283$ git diff
1284diff --cc file.txt
1285index 802992c,2b60207..0000000
1286--- a/file.txt
1287+++ b/file.txt
1288@@@ -1,1 -1,1 +1,5 @@@
1289++<<<<<<< HEAD:file.txt
1290 +Hello world
1291++=======
1292+ Goodbye
1293++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1294-------------------------------------------------
1295
1130845b 1296Recall that the commit which will be committed after we resolve this
d19fbc3c
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1297conflict will have two parents instead of the usual one: one parent
1298will be HEAD, the tip of the current branch; the other will be the
1299tip of the other branch, which is stored temporarily in MERGE_HEAD.
1300
ef561ac7
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1301During the merge, the index holds three versions of each file. Each of
1302these three "file stages" represents a different version of the file:
1303
1304-------------------------------------------------
1305$ git show :1:file.txt # the file in a common ancestor of both branches
4209752d
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1306$ git show :2:file.txt # the version from HEAD.
1307$ git show :3:file.txt # the version from MERGE_HEAD.
ef561ac7
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1308-------------------------------------------------
1309
4209752d
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1310When you ask linkgit:git-diff[1] to show the conflicts, it runs a
1311three-way diff between the conflicted merge results in the work tree with
1312stages 2 and 3 to show only hunks whose contents come from both sides,
1313mixed (in other words, when a hunk's merge results come only from stage 2,
1314that part is not conflicting and is not shown. Same for stage 3).
ef561ac7
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1315
1316The diff above shows the differences between the working-tree version of
1317file.txt and the stage 2 and stage 3 versions. So instead of preceding
1318each line by a single "+" or "-", it now uses two columns: the first
1319column is used for differences between the first parent and the working
1320directory copy, and the second for differences between the second parent
1321and the working directory copy. (See the "COMBINED DIFF FORMAT" section
5162e697 1322of linkgit:git-diff-files[1] for a details of the format.)
ef561ac7
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1323
1324After resolving the conflict in the obvious way (but before updating the
1325index), the diff will look like:
d19fbc3c
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1326
1327-------------------------------------------------
1328$ git diff
1329diff --cc file.txt
1330index 802992c,2b60207..0000000
1331--- a/file.txt
1332+++ b/file.txt
1333@@@ -1,1 -1,1 +1,1 @@@
1334- Hello world
1335 -Goodbye
1336++Goodbye world
1337-------------------------------------------------
1338
1339This shows that our resolved version deleted "Hello world" from the
1340first parent, deleted "Goodbye" from the second parent, and added
1341"Goodbye world", which was previously absent from both.
1342
ef561ac7
BF
1343Some special diff options allow diffing the working directory against
1344any of these stages:
1345
1346-------------------------------------------------
1347$ git diff -1 file.txt # diff against stage 1
1348$ git diff --base file.txt # same as the above
1349$ git diff -2 file.txt # diff against stage 2
1350$ git diff --ours file.txt # same as the above
1351$ git diff -3 file.txt # diff against stage 3
1352$ git diff --theirs file.txt # same as the above.
1353-------------------------------------------------
1354
0cafe944 1355The linkgit:git-log[1] and linkgit:gitk[1] commands also provide special help
ef561ac7 1356for merges:
d19fbc3c
BF
1357
1358-------------------------------------------------
1359$ git log --merge
ef561ac7 1360$ gitk --merge
d19fbc3c
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1361-------------------------------------------------
1362
ef561ac7
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1363These will display all commits which exist only on HEAD or on
1364MERGE_HEAD, and which touch an unmerged file.
d19fbc3c 1365
5162e697 1366You may also use linkgit:git-mergetool[1], which lets you merge the
c7719fbe 1367unmerged files using external tools such as Emacs or kdiff3.
c64415e2 1368
ef561ac7 1369Each time you resolve the conflicts in a file and update the index:
d19fbc3c
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1370
1371-------------------------------------------------
1372$ git add file.txt
d19fbc3c
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1373-------------------------------------------------
1374
ef561ac7 1375the different stages of that file will be "collapsed", after which
6127c086 1376`git diff` will (by default) no longer show diffs for that file.
d19fbc3c
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1377
1378[[undoing-a-merge]]
ae25c67a 1379Undoing a merge
d19fbc3c
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1380---------------
1381
1382If you get stuck and decide to just give up and throw the whole mess
1383away, you can always return to the pre-merge state with
1384
1385-------------------------------------------------
1386$ git reset --hard HEAD
1387-------------------------------------------------
1388
1130845b 1389Or, if you've already committed the merge that you want to throw away,
d19fbc3c
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1390
1391-------------------------------------------------
1c73bb0e 1392$ git reset --hard ORIG_HEAD
d19fbc3c
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1393-------------------------------------------------
1394
1395However, this last command can be dangerous in some cases--never
1396throw away a commit you have already committed if that commit may
1397itself have been merged into another branch, as doing so may confuse
1398further merges.
1399
e34caace 1400[[fast-forwards]]
d19fbc3c
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1401Fast-forward merges
1402-------------------
1403
1404There is one special case not mentioned above, which is treated
1405differently. Normally, a merge results in a merge commit, with two
1406parents, one pointing at each of the two lines of development that
1407were merged.
1408
59723040
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1409However, if the current branch is a descendant of the other--so every
1410commit present in the one is already contained in the other--then git
a75d7b54 1411just performs a "fast-forward"; the head of the current branch is moved
59723040
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1412forward to point at the head of the merged-in branch, without any new
1413commits being created.
d19fbc3c 1414
e34caace 1415[[fixing-mistakes]]
b684f830
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1416Fixing mistakes
1417---------------
1418
1419If you've messed up the working tree, but haven't yet committed your
1420mistake, you can return the entire working tree to the last committed
1421state with
1422
1423-------------------------------------------------
1424$ git reset --hard HEAD
1425-------------------------------------------------
1426
1427If you make a commit that you later wish you hadn't, there are two
1428fundamentally different ways to fix the problem:
1429
1430 1. You can create a new commit that undoes whatever was done
93cbbd71 1431 by the old commit. This is the correct thing if your
b684f830
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1432 mistake has already been made public.
1433
1434 2. You can go back and modify the old commit. You should
1435 never do this if you have already made the history public;
1436 git does not normally expect the "history" of a project to
1437 change, and cannot correctly perform repeated merges from
1438 a branch that has had its history changed.
1439
e34caace 1440[[reverting-a-commit]]
b684f830
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1441Fixing a mistake with a new commit
1442~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1443
1444Creating a new commit that reverts an earlier change is very easy;
5162e697 1445just pass the linkgit:git-revert[1] command a reference to the bad
b684f830
BF
1446commit; for example, to revert the most recent commit:
1447
1448-------------------------------------------------
1449$ git revert HEAD
1450-------------------------------------------------
1451
1452This will create a new commit which undoes the change in HEAD. You
1453will be given a chance to edit the commit message for the new commit.
1454
1455You can also revert an earlier change, for example, the next-to-last:
1456
1457-------------------------------------------------
1458$ git revert HEAD^
1459-------------------------------------------------
1460
1461In this case git will attempt to undo the old change while leaving
1462intact any changes made since then. If more recent changes overlap
1463with the changes to be reverted, then you will be asked to fix
1464conflicts manually, just as in the case of <<resolving-a-merge,
1465resolving a merge>>.
1466
7cb192ea
BF
1467[[fixing-a-mistake-by-rewriting-history]]
1468Fixing a mistake by rewriting history
b684f830
BF
1469~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1470
1471If the problematic commit is the most recent commit, and you have not
1472yet made that commit public, then you may just
6127c086 1473<<undoing-a-merge,destroy it using `git reset`>>.
b684f830
BF
1474
1475Alternatively, you
1476can edit the working directory and update the index to fix your
1477mistake, just as if you were going to <<how-to-make-a-commit,create a
1478new commit>>, then run
1479
1480-------------------------------------------------
1481$ git commit --amend
1482-------------------------------------------------
1483
1484which will replace the old commit by a new commit incorporating your
1485changes, giving you a chance to edit the old commit message first.
1486
1487Again, you should never do this to a commit that may already have
5162e697 1488been merged into another branch; use linkgit:git-revert[1] instead in
b684f830
BF
1489that case.
1490
7cb192ea 1491It is also possible to replace commits further back in the history, but
b684f830
BF
1492this is an advanced topic to be left for
1493<<cleaning-up-history,another chapter>>.
1494
e34caace 1495[[checkout-of-path]]
b684f830
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1496Checking out an old version of a file
1497~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1498
1499In the process of undoing a previous bad change, you may find it
1500useful to check out an older version of a particular file using
6127c086 1501linkgit:git-checkout[1]. We've used `git checkout` before to switch
b684f830
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1502branches, but it has quite different behavior if it is given a path
1503name: the command
1504
1505-------------------------------------------------
1506$ git checkout HEAD^ path/to/file
1507-------------------------------------------------
1508
1509replaces path/to/file by the contents it had in the commit HEAD^, and
1510also updates the index to match. It does not change branches.
1511
1512If you just want to look at an old version of the file, without
1513modifying the working directory, you can do that with
5162e697 1514linkgit:git-show[1]:
b684f830
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1515
1516-------------------------------------------------
ed4eb0d8 1517$ git show HEAD^:path/to/file
b684f830
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1518-------------------------------------------------
1519
1520which will display the given version of the file.
1521
7a7cc594
JH
1522[[interrupted-work]]
1523Temporarily setting aside work in progress
1524~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1525
1526While you are in the middle of working on something complicated, you
1527find an unrelated but obvious and trivial bug. You would like to fix it
5162e697 1528before continuing. You can use linkgit:git-stash[1] to save the current
7a7cc594
JH
1529state of your work, and after fixing the bug (or, optionally after doing
1530so on a different branch and then coming back), unstash the
1531work-in-progress changes.
1532
1533------------------------------------------------
7a85f6ae 1534$ git stash save "work in progress for foo feature"
7a7cc594
JH
1535------------------------------------------------
1536
1537This command will save your changes away to the `stash`, and
1538reset your working tree and the index to match the tip of your
1539current branch. Then you can make your fix as usual.
1540
1541------------------------------------------------
1542... edit and test ...
1543$ git commit -a -m "blorpl: typofix"
1544------------------------------------------------
1545
1546After that, you can go back to what you were working on with
7b8988e1 1547`git stash pop`:
7a7cc594
JH
1548
1549------------------------------------------------
7b8988e1 1550$ git stash pop
7a7cc594
JH
1551------------------------------------------------
1552
1553
e34caace 1554[[ensuring-good-performance]]
d19fbc3c
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1555Ensuring good performance
1556-------------------------
1557
1558On large repositories, git depends on compression to keep the history
06ada152 1559information from taking up too much space on disk or in memory.
d19fbc3c
BF
1560
1561This compression is not performed automatically. Therefore you
5162e697 1562should occasionally run linkgit:git-gc[1]:
d19fbc3c
BF
1563
1564-------------------------------------------------
1565$ git gc
1566-------------------------------------------------
1567
17217090 1568to recompress the archive. This can be very time-consuming, so
6127c086 1569you may prefer to run `git gc` when you are not doing other work.
d19fbc3c 1570
e34caace
BF
1571
1572[[ensuring-reliability]]
11e016a3
BF
1573Ensuring reliability
1574--------------------
1575
e34caace 1576[[checking-for-corruption]]
11e016a3
BF
1577Checking the repository for corruption
1578~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1579
5162e697 1580The linkgit:git-fsck[1] command runs a number of self-consistency checks
1191ee18 1581on the repository, and reports on any problems. This may take some
21dcb3b7
BF
1582time. The most common warning by far is about "dangling" objects:
1583
1584-------------------------------------------------
04e50e94 1585$ git fsck
21dcb3b7
BF
1586dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1587dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1588dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1589dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1590dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1591dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1592dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1593dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1594...
1595-------------------------------------------------
1596
59723040 1597Dangling objects are not a problem. At worst they may take up a little
54782859 1598extra disk space. They can sometimes provide a last-resort method for
208641cf 1599recovering lost work--see <<dangling-objects>> for details.
1cdade2c 1600
e34caace 1601[[recovering-lost-changes]]
11e016a3
BF
1602Recovering lost changes
1603~~~~~~~~~~~~~~~~~~~~~~~
1604
e34caace 1605[[reflogs]]
559e4d7a
BF
1606Reflogs
1607^^^^^^^
1608
5162e697 1609Say you modify a branch with `linkgit:git-reset[1] --hard`, and then
559e4d7a
BF
1610realize that the branch was the only reference you had to that point in
1611history.
1612
1613Fortunately, git also keeps a log, called a "reflog", of all the
1614previous values of each branch. So in this case you can still find the
a6080a0a 1615old history using, for example,
559e4d7a
BF
1616
1617-------------------------------------------------
1618$ git log master@{1}
1619-------------------------------------------------
1620
e502c2c3
SO
1621This lists the commits reachable from the previous version of the
1622"master" branch head. This syntax can be used with any git command
1623that accepts a commit, not just with git log. Some other examples:
559e4d7a
BF
1624
1625-------------------------------------------------
1626$ git show master@{2} # See where the branch pointed 2,
1627$ git show master@{3} # 3, ... changes ago.
1628$ gitk master@{yesterday} # See where it pointed yesterday,
1629$ gitk master@{"1 week ago"} # ... or last week
953f3d6f
BF
1630$ git log --walk-reflogs master # show reflog entries for master
1631-------------------------------------------------
1632
1633A separate reflog is kept for the HEAD, so
1634
1635-------------------------------------------------
1636$ git show HEAD@{"1 week ago"}
559e4d7a
BF
1637-------------------------------------------------
1638
953f3d6f
BF
1639will show what HEAD pointed to one week ago, not what the current branch
1640pointed to one week ago. This allows you to see the history of what
1641you've checked out.
1642
559e4d7a 1643The reflogs are kept by default for 30 days, after which they may be
5162e697 1644pruned. See linkgit:git-reflog[1] and linkgit:git-gc[1] to learn
559e4d7a 1645how to control this pruning, and see the "SPECIFYING REVISIONS"
9d83e382 1646section of linkgit:gitrevisions[7] for details.
559e4d7a
BF
1647
1648Note that the reflog history is very different from normal git history.
1649While normal history is shared by every repository that works on the
1650same project, the reflog history is not shared: it tells you only about
1651how the branches in your local repository have changed over time.
1652
59723040 1653[[dangling-object-recovery]]
559e4d7a
BF
1654Examining dangling objects
1655^^^^^^^^^^^^^^^^^^^^^^^^^^
1656
59723040
BF
1657In some situations the reflog may not be able to save you. For example,
1658suppose you delete a branch, then realize you need the history it
1659contained. The reflog is also deleted; however, if you have not yet
1660pruned the repository, then you may still be able to find the lost
6127c086 1661commits in the dangling objects that `git fsck` reports. See
59723040 1662<<dangling-objects>> for the details.
559e4d7a
BF
1663
1664-------------------------------------------------
1665$ git fsck
1666dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1667dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1668dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1669...
1670-------------------------------------------------
1671
aacd404e 1672You can examine
559e4d7a
BF
1673one of those dangling commits with, for example,
1674
1675------------------------------------------------
1676$ gitk 7281251ddd --not --all
1677------------------------------------------------
1678
1679which does what it sounds like: it says that you want to see the commit
1680history that is described by the dangling commit(s), but not the
1681history that is described by all your existing branches and tags. Thus
1682you get exactly the history reachable from that commit that is lost.
1683(And notice that it might not be just one commit: we only report the
1684"tip of the line" as being dangling, but there might be a whole deep
79c96c57 1685and complex commit history that was dropped.)
559e4d7a
BF
1686
1687If you decide you want the history back, you can always create a new
1688reference pointing to it, for example, a new branch:
1689
1690------------------------------------------------
a6080a0a 1691$ git branch recovered-branch 7281251ddd
559e4d7a
BF
1692------------------------------------------------
1693
59723040
BF
1694Other types of dangling objects (blobs and trees) are also possible, and
1695dangling objects can arise in other situations.
1696
11e016a3 1697
e34caace 1698[[sharing-development]]
d19fbc3c 1699Sharing development with others
b684f830 1700===============================
d19fbc3c 1701
aa971cb9 1702[[getting-updates-With-git-pull]]
6127c086 1703Getting updates with git pull
b684f830 1704-----------------------------
d19fbc3c 1705
e63ec003 1706After you clone a repository and commit a few changes of your own, you
d19fbc3c
BF
1707may wish to check the original repository for updates and merge them
1708into your own work.
1709
aa971cb9 1710We have already seen <<Updating-a-repository-With-git-fetch,how to
0e615b25 1711keep remote-tracking branches up to date>> with linkgit:git-fetch[1],
d19fbc3c
BF
1712and how to merge two branches. So you can merge in changes from the
1713original repository's master branch with:
1714
1715-------------------------------------------------
1716$ git fetch
1717$ git merge origin/master
1718-------------------------------------------------
1719
5162e697 1720However, the linkgit:git-pull[1] command provides a way to do this in
d19fbc3c
BF
1721one step:
1722
1723-------------------------------------------------
1724$ git pull origin master
1725-------------------------------------------------
1726
66a062a1
MM
1727In fact, if you have "master" checked out, then this branch has been
1728configured by "git clone" to get changes from the HEAD branch of the
1729origin repository. So often you can
0eb4f7cd 1730accomplish the above with just a simple
d19fbc3c
BF
1731
1732-------------------------------------------------
1733$ git pull
1734-------------------------------------------------
1735
66a062a1
MM
1736This command will fetch changes from the remote branches to your
1737remote-tracking branches `origin/*`, and merge the default branch into
1738the current branch.
1739
29b9a66f
MM
1740More generally, a branch that is created from a remote-tracking branch
1741will pull
0eb4f7cd
BF
1742by default from that branch. See the descriptions of the
1743branch.<name>.remote and branch.<name>.merge options in
5162e697
DM
1744linkgit:git-config[1], and the discussion of the `--track` option in
1745linkgit:git-checkout[1], to learn how to control these defaults.
d19fbc3c
BF
1746
1747In addition to saving you keystrokes, "git pull" also helps you by
1748producing a default commit message documenting the branch and
1749repository that you pulled from.
1750
1751(But note that no such commit will be created in the case of a
a75d7b54 1752<<fast-forwards,fast-forward>>; instead, your branch will just be
79c96c57 1753updated to point to the latest commit from the upstream branch.)
d19fbc3c 1754
6127c086 1755The `git pull` command can also be given "." as the "remote" repository,
1191ee18 1756in which case it just merges in a branch from the current repository; so
4c63ff45
BF
1757the commands
1758
1759-------------------------------------------------
1760$ git pull . branch
1761$ git merge branch
1762-------------------------------------------------
1763
1764are roughly equivalent. The former is actually very commonly used.
1765
e34caace 1766[[submitting-patches]]
d19fbc3c 1767Submitting patches to a project
b684f830 1768-------------------------------
d19fbc3c
BF
1769
1770If you just have a few changes, the simplest way to submit them may
1771just be to send them as patches in email:
1772
5162e697 1773First, use linkgit:git-format-patch[1]; for example:
d19fbc3c
BF
1774
1775-------------------------------------------------
eb6ae7f4 1776$ git format-patch origin
d19fbc3c
BF
1777-------------------------------------------------
1778
1779will produce a numbered series of files in the current directory, one
1780for each patch in the current branch but not in origin/HEAD.
1781
1782You can then import these into your mail client and send them by
1783hand. However, if you have a lot to send at once, you may prefer to
5162e697 1784use the linkgit:git-send-email[1] script to automate the process.
d19fbc3c
BF
1785Consult the mailing list for your project first to determine how they
1786prefer such patches be handled.
1787
e34caace 1788[[importing-patches]]
d19fbc3c 1789Importing patches to a project
b684f830 1790------------------------------
d19fbc3c 1791
5162e697 1792Git also provides a tool called linkgit:git-am[1] (am stands for
d19fbc3c
BF
1793"apply mailbox"), for importing such an emailed series of patches.
1794Just save all of the patch-containing messages, in order, into a
1795single mailbox file, say "patches.mbox", then run
1796
1797-------------------------------------------------
eb6ae7f4 1798$ git am -3 patches.mbox
d19fbc3c
BF
1799-------------------------------------------------
1800
1801Git will apply each patch in order; if any conflicts are found, it
1802will stop, and you can fix the conflicts as described in
01997b4a
BF
1803"<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells
1804git to perform a merge; if you would prefer it just to abort and
1805leave your tree and index untouched, you may omit that option.)
1806
1807Once the index is updated with the results of the conflict
1808resolution, instead of creating a new commit, just run
d19fbc3c
BF
1809
1810-------------------------------------------------
1811$ git am --resolved
1812-------------------------------------------------
1813
1814and git will create the commit for you and continue applying the
1815remaining patches from the mailbox.
1816
1817The final result will be a series of commits, one for each patch in
1818the original mailbox, with authorship and commit log message each
1819taken from the message containing each patch.
1820
eda69449
BF
1821[[public-repositories]]
1822Public git repositories
1823-----------------------
d19fbc3c 1824
6e30fb0c
DK
1825Another way to submit changes to a project is to tell the maintainer
1826of that project to pull the changes from your repository using
aa971cb9 1827linkgit:git-pull[1]. In the section "<<getting-updates-With-git-pull,
6127c086 1828Getting updates with `git pull`>>" we described this as a way to get
6e30fb0c
DK
1829updates from the "main" repository, but it works just as well in the
1830other direction.
d19fbc3c 1831
eda69449
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1832If you and the maintainer both have accounts on the same machine, then
1833you can just pull changes from each other's repositories directly;
11d51533 1834commands that accept repository URLs as arguments will also accept a
eda69449 1835local directory name:
d19fbc3c
BF
1836
1837-------------------------------------------------
1838$ git clone /path/to/repository
1839$ git pull /path/to/other/repository
1840-------------------------------------------------
1841
c9016158 1842or an ssh URL:
11d51533
BF
1843
1844-------------------------------------------------
1845$ git clone ssh://yourhost/~you/repository
1846-------------------------------------------------
1847
1848For projects with few developers, or for synchronizing a few private
1849repositories, this may be all you need.
1850
eda69449
BF
1851However, the more common way to do this is to maintain a separate public
1852repository (usually on a different host) for others to pull changes
1853from. This is usually more convenient, and allows you to cleanly
1854separate private work in progress from publicly visible work.
d19fbc3c
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1855
1856You will continue to do your day-to-day work in your personal
1857repository, but periodically "push" changes from your personal
1858repository into your public repository, allowing other developers to
1859pull from that repository. So the flow of changes, in a situation
1860where there is one other developer with a public repository, looks
1861like this:
1862
1863 you push
1864 your personal repo ------------------> your public repo
a6080a0a 1865 ^ |
d19fbc3c
BF
1866 | |
1867 | you pull | they pull
1868 | |
1869 | |
1870 | they push V
1871 their public repo <------------------- their repo
1872
11d51533
BF
1873We explain how to do this in the following sections.
1874
eda69449
BF
1875[[setting-up-a-public-repository]]
1876Setting up a public repository
1877~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1878
1879Assume your personal repository is in the directory ~/proj. We
6127c086 1880first create a new clone of the repository and tell `git daemon` that it
eda69449 1881is meant to be public:
d19fbc3c
BF
1882
1883-------------------------------------------------
52c80037 1884$ git clone --bare ~/proj proj.git
eda69449 1885$ touch proj.git/git-daemon-export-ok
d19fbc3c
BF
1886-------------------------------------------------
1887
52c80037 1888The resulting directory proj.git contains a "bare" git repository--it is
eda69449
BF
1889just the contents of the ".git" directory, without any files checked out
1890around it.
d19fbc3c 1891
c64415e2 1892Next, copy proj.git to the server where you plan to host the
d19fbc3c
BF
1893public repository. You can use scp, rsync, or whatever is most
1894convenient.
1895
eda69449
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1896[[exporting-via-git]]
1897Exporting a git repository via the git protocol
1898~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1899
1900This is the preferred method.
1901
1902If someone else administers the server, they should tell you what
c9016158 1903directory to put the repository in, and what git:// URL it will appear
eda69449 1904at. You can then skip to the section
d19fbc3c
BF
1905"<<pushing-changes-to-a-public-repository,Pushing changes to a public
1906repository>>", below.
1907
5162e697 1908Otherwise, all you need to do is start linkgit:git-daemon[1]; it will
eda69449
BF
1909listen on port 9418. By default, it will allow access to any directory
1910that looks like a git directory and contains the magic file
6127c086 1911git-daemon-export-ok. Passing some directory paths as `git daemon`
eda69449
BF
1912arguments will further restrict the exports to those paths.
1913
6127c086 1914You can also run `git daemon` as an inetd service; see the
5162e697 1915linkgit:git-daemon[1] man page for details. (See especially the
eda69449 1916examples section.)
d19fbc3c
BF
1917
1918[[exporting-via-http]]
1919Exporting a git repository via http
eda69449 1920~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
1921
1922The git protocol gives better performance and reliability, but on a
1923host with a web server set up, http exports may be simpler to set up.
1924
1925All you need to do is place the newly created bare git repository in
1926a directory that is exported by the web server, and make some
1927adjustments to give web clients some extra information they need:
1928
1929-------------------------------------------------
1930$ mv proj.git /home/you/public_html/proj.git
1931$ cd proj.git
c64415e2 1932$ git --bare update-server-info
7dce9918 1933$ mv hooks/post-update.sample hooks/post-update
d19fbc3c
BF
1934-------------------------------------------------
1935
1936(For an explanation of the last two lines, see
6998e4db 1937linkgit:git-update-server-info[1] and linkgit:githooks[5].)
d19fbc3c 1938
c9016158
RW
1939Advertise the URL of proj.git. Anybody else should then be able to
1940clone or pull from that URL, for example with a command line like:
d19fbc3c
BF
1941
1942-------------------------------------------------
1943$ git clone http://yourserver.com/~you/proj.git
1944-------------------------------------------------
1945
1946(See also
1947link:howto/setup-git-server-over-http.txt[setup-git-server-over-http]
1948for a slightly more sophisticated setup using WebDAV which also
1949allows pushing over http.)
1950
d19fbc3c
BF
1951[[pushing-changes-to-a-public-repository]]
1952Pushing changes to a public repository
eda69449 1953~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 1954
eda69449 1955Note that the two techniques outlined above (exporting via
d19fbc3c
BF
1956<<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other
1957maintainers to fetch your latest changes, but they do not allow write
1958access, which you will need to update the public repository with the
1959latest changes created in your private repository.
1960
5162e697 1961The simplest way to do this is using linkgit:git-push[1] and ssh; to
d19fbc3c
BF
1962update the remote branch named "master" with the latest state of your
1963branch named "master", run
1964
1965-------------------------------------------------
1966$ git push ssh://yourserver.com/~you/proj.git master:master
1967-------------------------------------------------
1968
1969or just
1970
1971-------------------------------------------------
1972$ git push ssh://yourserver.com/~you/proj.git master
1973-------------------------------------------------
1974
6127c086 1975As with `git fetch`, `git push` will complain if this does not result in a
a75d7b54 1976<<fast-forwards,fast-forward>>; see the following section for details on
81eb417a 1977handling this case.
d19fbc3c 1978
11d51533
BF
1979Note that the target of a "push" is normally a
1980<<def_bare_repository,bare>> repository. You can also push to a
1981repository that has a checked-out working tree, but the working tree
1982will not be updated by the push. This may lead to unexpected results if
1983the branch you push to is the currently checked-out branch!
1984
6127c086 1985As with `git fetch`, you may also set up configuration options to
d19fbc3c
BF
1986save typing; so, for example, after
1987
1988-------------------------------------------------
c64415e2 1989$ cat >>.git/config <<EOF
d19fbc3c
BF
1990[remote "public-repo"]
1991 url = ssh://yourserver.com/~you/proj.git
1992EOF
1993-------------------------------------------------
1994
1995you should be able to perform the above push with just
1996
1997-------------------------------------------------
1998$ git push public-repo master
1999-------------------------------------------------
2000
2001See the explanations of the remote.<name>.url, branch.<name>.remote,
5162e697 2002and remote.<name>.push options in linkgit:git-config[1] for
d19fbc3c
BF
2003details.
2004
81eb417a
BF
2005[[forcing-push]]
2006What to do when a push fails
2007~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2008
a75d7b54 2009If a push would not result in a <<fast-forwards,fast-forward>> of the
81eb417a
BF
2010remote branch, then it will fail with an error like:
2011
2012-------------------------------------------------
2013error: remote 'refs/heads/master' is not an ancestor of
2014 local 'refs/heads/master'.
2015 Maybe you are not up-to-date and need to pull first?
2016error: failed to push to 'ssh://yourserver.com/~you/proj.git'
2017-------------------------------------------------
2018
2019This can happen, for example, if you:
2020
6127c086
FC
2021 - use `git reset --hard` to remove already-published commits, or
2022 - use `git commit --amend` to replace already-published commits
7cb192ea 2023 (as in <<fixing-a-mistake-by-rewriting-history>>), or
6127c086 2024 - use `git rebase` to rebase any already-published commits (as
81eb417a
BF
2025 in <<using-git-rebase>>).
2026
6127c086 2027You may force `git push` to perform the update anyway by preceding the
81eb417a
BF
2028branch name with a plus sign:
2029
2030-------------------------------------------------
2031$ git push ssh://yourserver.com/~you/proj.git +master
2032-------------------------------------------------
2033
2034Normally whenever a branch head in a public repository is modified, it
9e5d87d4 2035is modified to point to a descendant of the commit that it pointed to
81eb417a 2036before. By forcing a push in this situation, you break that convention.
aa971cb9 2037(See <<problems-With-rewriting-history>>.)
81eb417a
BF
2038
2039Nevertheless, this is a common practice for people that need a simple
2040way to publish a work-in-progress patch series, and it is an acceptable
2041compromise as long as you warn other developers that this is how you
2042intend to manage the branch.
2043
2044It's also possible for a push to fail in this way when other people have
2045the right to push to the same repository. In that case, the correct
843c81dc
EH
2046solution is to retry the push after first updating your work: either by a
2047pull, or by a fetch followed by a rebase; see the
81eb417a 2048<<setting-up-a-shared-repository,next section>> and
6998e4db 2049linkgit:gitcvs-migration[7] for more.
81eb417a 2050
e34caace 2051[[setting-up-a-shared-repository]]
d19fbc3c 2052Setting up a shared repository
eda69449 2053~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
2054
2055Another way to collaborate is by using a model similar to that
2056commonly used in CVS, where several developers with special rights
2057all push to and pull from a single shared repository. See
6998e4db 2058linkgit:gitcvs-migration[7] for instructions on how to
d19fbc3c
BF
2059set this up.
2060
8fae2225
BF
2061However, while there is nothing wrong with git's support for shared
2062repositories, this mode of operation is not generally recommended,
2063simply because the mode of collaboration that git supports--by
2064exchanging patches and pulling from public repositories--has so many
2065advantages over the central shared repository:
2066
2067 - Git's ability to quickly import and merge patches allows a
2068 single maintainer to process incoming changes even at very
6127c086 2069 high rates. And when that becomes too much, `git pull` provides
8fae2225
BF
2070 an easy way for that maintainer to delegate this job to other
2071 maintainers while still allowing optional review of incoming
2072 changes.
2073 - Since every developer's repository has the same complete copy
2074 of the project history, no repository is special, and it is
2075 trivial for another developer to take over maintenance of a
2076 project, either by mutual agreement, or because a maintainer
2077 becomes unresponsive or difficult to work with.
2078 - The lack of a central group of "committers" means there is
2079 less need for formal decisions about who is "in" and who is
2080 "out".
2081
e34caace 2082[[setting-up-gitweb]]
eda69449
BF
2083Allowing web browsing of a repository
2084~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 2085
a8cd1402
BF
2086The gitweb cgi script provides users an easy way to browse your
2087project's files and history without having to install git; see the file
04483524 2088gitweb/INSTALL in the git source tree for instructions on setting it up.
d19fbc3c 2089
e34caace 2090[[sharing-development-examples]]
b684f830
BF
2091Examples
2092--------
d19fbc3c 2093
9e2163ea
BF
2094[[maintaining-topic-branches]]
2095Maintaining topic branches for a Linux subsystem maintainer
2096~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2097
2098This describes how Tony Luck uses git in his role as maintainer of the
2099IA64 architecture for the Linux kernel.
2100
2101He uses two public branches:
2102
2103 - A "test" tree into which patches are initially placed so that they
2104 can get some exposure when integrated with other ongoing development.
2105 This tree is available to Andrew for pulling into -mm whenever he
2106 wants.
2107
2108 - A "release" tree into which tested patches are moved for final sanity
2109 checking, and as a vehicle to send them upstream to Linus (by sending
2110 him a "please pull" request.)
2111
2112He also uses a set of temporary branches ("topic branches"), each
2113containing a logical grouping of patches.
2114
2115To set this up, first create your work tree by cloning Linus's public
2116tree:
2117
2118-------------------------------------------------
2119$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work
2120$ cd work
2121-------------------------------------------------
2122
29b9a66f 2123Linus's tree will be stored in the remote-tracking branch named origin/master,
5162e697
DM
2124and can be updated using linkgit:git-fetch[1]; you can track other
2125public trees using linkgit:git-remote[1] to set up a "remote" and
2126linkgit:git-fetch[1] to keep them up-to-date; see
6e30fb0c 2127<<repositories-and-branches>>.
9e2163ea
BF
2128
2129Now create the branches in which you are going to work; these start out
2130at the current tip of origin/master branch, and should be set up (using
5162e697 2131the --track option to linkgit:git-branch[1]) to merge changes in from
9e2163ea
BF
2132Linus by default.
2133
2134-------------------------------------------------
2135$ git branch --track test origin/master
2136$ git branch --track release origin/master
2137-------------------------------------------------
2138
5162e697 2139These can be easily kept up to date using linkgit:git-pull[1].
9e2163ea
BF
2140
2141-------------------------------------------------
2142$ git checkout test && git pull
2143$ git checkout release && git pull
2144-------------------------------------------------
2145
2146Important note! If you have any local changes in these branches, then
2147this merge will create a commit object in the history (with no local
a75d7b54 2148changes git will simply do a "fast-forward" merge). Many people dislike
9e2163ea
BF
2149the "noise" that this creates in the Linux history, so you should avoid
2150doing this capriciously in the "release" branch, as these noisy commits
2151will become part of the permanent history when you ask Linus to pull
2152from the release branch.
2153
5162e697 2154A few configuration variables (see linkgit:git-config[1]) can
9e2163ea
BF
2155make it easy to push both branches to your public tree. (See
2156<<setting-up-a-public-repository>>.)
2157
2158-------------------------------------------------
2159$ cat >> .git/config <<EOF
2160[remote "mytree"]
2161 url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
2162 push = release
2163 push = test
2164EOF
2165-------------------------------------------------
2166
2167Then you can push both the test and release trees using
5162e697 2168linkgit:git-push[1]:
9e2163ea
BF
2169
2170-------------------------------------------------
2171$ git push mytree
2172-------------------------------------------------
2173
2174or push just one of the test and release branches using:
2175
2176-------------------------------------------------
2177$ git push mytree test
2178-------------------------------------------------
2179
2180or
2181
2182-------------------------------------------------
2183$ git push mytree release
2184-------------------------------------------------
2185
2186Now to apply some patches from the community. Think of a short
2187snappy name for a branch to hold this patch (or related group of
352953a5
TL
2188patches), and create a new branch from a recent stable tag of
2189Linus's branch. Picking a stable base for your branch will:
21901) help you: by avoiding inclusion of unrelated and perhaps lightly
2191tested changes
21922) help future bug hunters that use "git bisect" to find problems
9e2163ea
BF
2193
2194-------------------------------------------------
352953a5 2195$ git checkout -b speed-up-spinlocks v2.6.35
9e2163ea
BF
2196-------------------------------------------------
2197
2198Now you apply the patch(es), run some tests, and commit the change(s). If
2199the patch is a multi-part series, then you should apply each as a separate
2200commit to this branch.
2201
2202-------------------------------------------------
2203$ ... patch ... test ... commit [ ... patch ... test ... commit ]*
2204-------------------------------------------------
2205
2206When you are happy with the state of this change, you can pull it into the
2207"test" branch in preparation to make it public:
2208
2209-------------------------------------------------
2210$ git checkout test && git pull . speed-up-spinlocks
2211-------------------------------------------------
2212
2213It is unlikely that you would have any conflicts here ... but you might if you
2214spent a while on this step and had also pulled new versions from upstream.
2215
2216Some time later when enough time has passed and testing done, you can pull the
2217same branch into the "release" tree ready to go upstream. This is where you
2218see the value of keeping each patch (or patch series) in its own branch. It
2219means that the patches can be moved into the "release" tree in any order.
2220
2221-------------------------------------------------
2222$ git checkout release && git pull . speed-up-spinlocks
2223-------------------------------------------------
2224
2225After a while, you will have a number of branches, and despite the
2226well chosen names you picked for each of them, you may forget what
2227they are for, or what status they are in. To get a reminder of what
2228changes are in a specific branch, use:
2229
2230-------------------------------------------------
467c0197 2231$ git log linux..branchname | git shortlog
9e2163ea
BF
2232-------------------------------------------------
2233
06ada152 2234To see whether it has already been merged into the test or release branches,
9e2163ea
BF
2235use:
2236
2237-------------------------------------------------
2238$ git log test..branchname
2239-------------------------------------------------
2240
2241or
2242
2243-------------------------------------------------
2244$ git log release..branchname
2245-------------------------------------------------
2246
06ada152 2247(If this branch has not yet been merged, you will see some log entries.
9e2163ea
BF
2248If it has been merged, then there will be no output.)
2249
2250Once a patch completes the great cycle (moving from test to release,
2251then pulled by Linus, and finally coming back into your local
06ada152 2252"origin/master" branch), the branch for this change is no longer needed.
9e2163ea
BF
2253You detect this when the output from:
2254
2255-------------------------------------------------
2256$ git log origin..branchname
2257-------------------------------------------------
2258
2259is empty. At this point the branch can be deleted:
2260
2261-------------------------------------------------
2262$ git branch -d branchname
2263-------------------------------------------------
2264
2265Some changes are so trivial that it is not necessary to create a separate
2266branch and then merge into each of the test and release branches. For
2267these changes, just apply directly to the "release" branch, and then
2268merge that into the "test" branch.
2269
2270To create diffstat and shortlog summaries of changes to include in a "please
2271pull" request to Linus you can use:
2272
2273-------------------------------------------------
2274$ git diff --stat origin..release
2275-------------------------------------------------
2276
2277and
2278
2279-------------------------------------------------
2280$ git log -p origin..release | git shortlog
2281-------------------------------------------------
2282
2283Here are some of the scripts that simplify all this even further.
2284
2285-------------------------------------------------
2286==== update script ====
2287# Update a branch in my GIT tree. If the branch to be updated
2288# is origin, then pull from kernel.org. Otherwise merge
2289# origin/master branch into test|release branch
2290
2291case "$1" in
2292test|release)
2293 git checkout $1 && git pull . origin
2294 ;;
2295origin)
fc74ecc1 2296 before=$(git rev-parse refs/remotes/origin/master)
9e2163ea 2297 git fetch origin
fc74ecc1 2298 after=$(git rev-parse refs/remotes/origin/master)
9e2163ea
BF
2299 if [ $before != $after ]
2300 then
2301 git log $before..$after | git shortlog
2302 fi
2303 ;;
2304*)
2305 echo "Usage: $0 origin|test|release" 1>&2
2306 exit 1
2307 ;;
2308esac
2309-------------------------------------------------
2310
2311-------------------------------------------------
2312==== merge script ====
2313# Merge a branch into either the test or release branch
2314
2315pname=$0
2316
2317usage()
2318{
2319 echo "Usage: $pname branch test|release" 1>&2
2320 exit 1
2321}
2322
fc74ecc1 2323git show-ref -q --verify -- refs/heads/"$1" || {
9e2163ea
BF
2324 echo "Can't see branch <$1>" 1>&2
2325 usage
fc74ecc1 2326}
9e2163ea
BF
2327
2328case "$2" in
2329test|release)
2330 if [ $(git log $2..$1 | wc -c) -eq 0 ]
2331 then
2332 echo $1 already merged into $2 1>&2
2333 exit 1
2334 fi
2335 git checkout $2 && git pull . $1
2336 ;;
2337*)
2338 usage
2339 ;;
2340esac
2341-------------------------------------------------
2342
2343-------------------------------------------------
2344==== status script ====
2345# report on status of my ia64 GIT tree
2346
2347gb=$(tput setab 2)
2348rb=$(tput setab 1)
2349restore=$(tput setab 9)
2350
2351if [ `git rev-list test..release | wc -c` -gt 0 ]
2352then
2353 echo $rb Warning: commits in release that are not in test $restore
2354 git log test..release
2355fi
2356
fc74ecc1 2357for branch in `git show-ref --heads | sed 's|^.*/||'`
9e2163ea
BF
2358do
2359 if [ $branch = test -o $branch = release ]
2360 then
2361 continue
2362 fi
2363
2364 echo -n $gb ======= $branch ====== $restore " "
2365 status=
2366 for ref in test release origin/master
2367 do
2368 if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]
2369 then
2370 status=$status${ref:0:1}
2371 fi
2372 done
2373 case $status in
2374 trl)
2375 echo $rb Need to pull into test $restore
2376 ;;
2377 rl)
2378 echo "In test"
2379 ;;
2380 l)
2381 echo "Waiting for linus"
2382 ;;
2383 "")
2384 echo $rb All done $restore
2385 ;;
2386 *)
2387 echo $rb "<$status>" $restore
2388 ;;
2389 esac
2390 git log origin/master..$branch | git shortlog
2391done
2392-------------------------------------------------
d19fbc3c 2393
d19fbc3c 2394
d19fbc3c 2395[[cleaning-up-history]]
4c63ff45
BF
2396Rewriting history and maintaining patch series
2397==============================================
2398
2399Normally commits are only added to a project, never taken away or
2400replaced. Git is designed with this assumption, and violating it will
2401cause git's merge machinery (for example) to do the wrong thing.
2402
2403However, there is a situation in which it can be useful to violate this
2404assumption.
2405
e34caace 2406[[patch-series]]
4c63ff45
BF
2407Creating the perfect patch series
2408---------------------------------
2409
2410Suppose you are a contributor to a large project, and you want to add a
2411complicated feature, and to present it to the other developers in a way
2412that makes it easy for them to read your changes, verify that they are
2413correct, and understand why you made each change.
2414
b181d57f 2415If you present all of your changes as a single patch (or commit), they
79c96c57 2416may find that it is too much to digest all at once.
4c63ff45
BF
2417
2418If you present them with the entire history of your work, complete with
2419mistakes, corrections, and dead ends, they may be overwhelmed.
2420
2421So the ideal is usually to produce a series of patches such that:
2422
2423 1. Each patch can be applied in order.
2424
2425 2. Each patch includes a single logical change, together with a
2426 message explaining the change.
2427
2428 3. No patch introduces a regression: after applying any initial
2429 part of the series, the resulting project still compiles and
2430 works, and has no bugs that it didn't have before.
2431
2432 4. The complete series produces the same end result as your own
2433 (probably much messier!) development process did.
2434
b181d57f
BF
2435We will introduce some tools that can help you do this, explain how to
2436use them, and then explain some of the problems that can arise because
2437you are rewriting history.
4c63ff45 2438
e34caace 2439[[using-git-rebase]]
6127c086 2440Keeping a patch series up to date using git rebase
4c63ff45
BF
2441--------------------------------------------------
2442
79c96c57
MC
2443Suppose that you create a branch "mywork" on a remote-tracking branch
2444"origin", and create some commits on top of it:
4c63ff45
BF
2445
2446-------------------------------------------------
2447$ git checkout -b mywork origin
2448$ vi file.txt
2449$ git commit
2450$ vi otherfile.txt
2451$ git commit
2452...
2453-------------------------------------------------
2454
2455You have performed no merges into mywork, so it is just a simple linear
2456sequence of patches on top of "origin":
2457
1dc71a91 2458................................................
fa8347b8 2459 o--o--O <-- origin
4c63ff45 2460 \
fa8347b8 2461 a--b--c <-- mywork
1dc71a91 2462................................................
4c63ff45
BF
2463
2464Some more interesting work has been done in the upstream project, and
2465"origin" has advanced:
2466
1dc71a91 2467................................................
4c63ff45
BF
2468 o--o--O--o--o--o <-- origin
2469 \
2470 a--b--c <-- mywork
1dc71a91 2471................................................
4c63ff45
BF
2472
2473At this point, you could use "pull" to merge your changes back in;
2474the result would create a new merge commit, like this:
2475
1dc71a91 2476................................................
4c63ff45
BF
2477 o--o--O--o--o--o <-- origin
2478 \ \
2479 a--b--c--m <-- mywork
1dc71a91 2480................................................
a6080a0a 2481
4c63ff45
BF
2482However, if you prefer to keep the history in mywork a simple series of
2483commits without any merges, you may instead choose to use
5162e697 2484linkgit:git-rebase[1]:
4c63ff45
BF
2485
2486-------------------------------------------------
2487$ git checkout mywork
2488$ git rebase origin
2489-------------------------------------------------
2490
b181d57f 2491This will remove each of your commits from mywork, temporarily saving
51ef1daa 2492them as patches (in a directory named ".git/rebase-apply"), update mywork to
b181d57f
BF
2493point at the latest version of origin, then apply each of the saved
2494patches to the new mywork. The result will look like:
4c63ff45
BF
2495
2496
1dc71a91 2497................................................
4c63ff45
BF
2498 o--o--O--o--o--o <-- origin
2499 \
2500 a'--b'--c' <-- mywork
1dc71a91 2501................................................
4c63ff45 2502
b181d57f 2503In the process, it may discover conflicts. In that case it will stop
6127c086 2504and allow you to fix the conflicts; after fixing conflicts, use `git add`
7a7d4ef6 2505to update the index with those contents, and then, instead of
6127c086 2506running `git commit`, just run
4c63ff45
BF
2507
2508-------------------------------------------------
2509$ git rebase --continue
2510-------------------------------------------------
2511
2512and git will continue applying the rest of the patches.
2513
b6cbca38 2514At any point you may use the `--abort` option to abort this process and
4c63ff45
BF
2515return mywork to the state it had before you started the rebase:
2516
2517-------------------------------------------------
2518$ git rebase --abort
2519-------------------------------------------------
2520
7cb192ea
BF
2521[[rewriting-one-commit]]
2522Rewriting a single commit
365aa199
BF
2523-------------------------
2524
7cb192ea 2525We saw in <<fixing-a-mistake-by-rewriting-history>> that you can replace the
365aa199
BF
2526most recent commit using
2527
2528-------------------------------------------------
2529$ git commit --amend
2530-------------------------------------------------
2531
2532which will replace the old commit by a new commit incorporating your
2533changes, giving you a chance to edit the old commit message first.
2534
5162e697 2535You can also use a combination of this and linkgit:git-rebase[1] to
7cb192ea
BF
2536replace a commit further back in your history and recreate the
2537intervening changes on top of it. First, tag the problematic commit
2538with
365aa199
BF
2539
2540-------------------------------------------------
2541$ git tag bad mywork~5
2542-------------------------------------------------
2543
6127c086 2544(Either gitk or `git log` may be useful for finding the commit.)
365aa199 2545
25d9f3fa
BF
2546Then check out that commit, edit it, and rebase the rest of the series
2547on top of it (note that we could check out the commit on a temporary
2548branch, but instead we're using a <<detached-head,detached head>>):
365aa199
BF
2549
2550-------------------------------------------------
25d9f3fa 2551$ git checkout bad
365aa199
BF
2552$ # make changes here and update the index
2553$ git commit --amend
25d9f3fa 2554$ git rebase --onto HEAD bad mywork
365aa199
BF
2555-------------------------------------------------
2556
25d9f3fa
BF
2557When you're done, you'll be left with mywork checked out, with the top
2558patches on mywork reapplied on top of your modified commit. You can
365aa199
BF
2559then clean up with
2560
2561-------------------------------------------------
365aa199
BF
2562$ git tag -d bad
2563-------------------------------------------------
2564
2565Note that the immutable nature of git history means that you haven't really
2566"modified" existing commits; instead, you have replaced the old commits with
2567new commits having new object names.
2568
e34caace 2569[[reordering-patch-series]]
4c63ff45
BF
2570Reordering or selecting from a patch series
2571-------------------------------------------
2572
5162e697 2573Given one existing commit, the linkgit:git-cherry-pick[1] command
b181d57f
BF
2574allows you to apply the change introduced by that commit and create a
2575new commit that records it. So, for example, if "mywork" points to a
2576series of patches on top of "origin", you might do something like:
2577
2578-------------------------------------------------
2579$ git checkout -b mywork-new origin
2580$ gitk origin..mywork &
2581-------------------------------------------------
2582
06ada152 2583and browse through the list of patches in the mywork branch using gitk,
b181d57f 2584applying them (possibly in a different order) to mywork-new using
6127c086 2585cherry-pick, and possibly modifying them as you go using `git commit --amend`.
5162e697 2586The linkgit:git-gui[1] command may also help as it allows you to
6e30fb0c
DK
2587individually select diff hunks for inclusion in the index (by
2588right-clicking on the diff hunk and choosing "Stage Hunk for Commit").
b181d57f 2589
6127c086 2590Another technique is to use `git format-patch` to create a series of
b181d57f 2591patches, then reset the state to before the patches:
4c63ff45 2592
b181d57f
BF
2593-------------------------------------------------
2594$ git format-patch origin
2595$ git reset --hard origin
2596-------------------------------------------------
4c63ff45 2597
b181d57f 2598Then modify, reorder, or eliminate patches as preferred before applying
5162e697 2599them again with linkgit:git-am[1].
4c63ff45 2600
e34caace 2601[[patch-series-tools]]
4c63ff45
BF
2602Other tools
2603-----------
2604
73a1d050 2605There are numerous other tools, such as StGit, which exist for the
79c96c57 2606purpose of maintaining a patch series. These are outside of the scope of
b181d57f 2607this manual.
4c63ff45 2608
aa971cb9 2609[[problems-With-rewriting-history]]
4c63ff45
BF
2610Problems with rewriting history
2611-------------------------------
2612
b181d57f
BF
2613The primary problem with rewriting the history of a branch has to do
2614with merging. Suppose somebody fetches your branch and merges it into
2615their branch, with a result something like this:
2616
1dc71a91 2617................................................
b181d57f
BF
2618 o--o--O--o--o--o <-- origin
2619 \ \
2620 t--t--t--m <-- their branch:
1dc71a91 2621................................................
b181d57f
BF
2622
2623Then suppose you modify the last three commits:
2624
1dc71a91 2625................................................
b181d57f
BF
2626 o--o--o <-- new head of origin
2627 /
2628 o--o--O--o--o--o <-- old head of origin
1dc71a91 2629................................................
b181d57f
BF
2630
2631If we examined all this history together in one repository, it will
2632look like:
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
2638 \ \
2639 t--t--t--m <-- their branch:
1dc71a91 2640................................................
b181d57f
BF
2641
2642Git has no way of knowing that the new head is an updated version of
2643the old head; it treats this situation exactly the same as it would if
2644two developers had independently done the work on the old and new heads
2645in parallel. At this point, if someone attempts to merge the new head
2646in to their branch, git will attempt to merge together the two (old and
2647new) lines of development, instead of trying to replace the old by the
2648new. The results are likely to be unexpected.
2649
2650You may still choose to publish branches whose history is rewritten,
2651and it may be useful for others to be able to fetch those branches in
2652order to examine or test them, but they should not attempt to pull such
2653branches into their own work.
2654
2655For true distributed development that supports proper merging,
2656published branches should never be rewritten.
2657
3fb00282
SP
2658[[bisect-merges]]
2659Why bisecting merge commits can be harder than bisecting linear history
2660-----------------------------------------------------------------------
2661
5162e697 2662The linkgit:git-bisect[1] command correctly handles history that
3fb00282
SP
2663includes merge commits. However, when the commit that it finds is a
2664merge commit, the user may need to work harder than usual to figure out
2665why that commit introduced a problem.
2666
2667Imagine this history:
2668
2669................................................
2670 ---Z---o---X---...---o---A---C---D
2671 \ /
2672 o---o---Y---...---o---B
2673................................................
2674
2675Suppose that on the upper line of development, the meaning of one
2676of the functions that exists at Z is changed at commit X. The
2677commits from Z leading to A change both the function's
2678implementation and all calling sites that exist at Z, as well
2679as new calling sites they add, to be consistent. There is no
2680bug at A.
2681
2682Suppose that in the meantime on the lower line of development somebody
2683adds a new calling site for that function at commit Y. The
2684commits from Z leading to B all assume the old semantics of that
2685function and the callers and the callee are consistent with each
2686other. There is no bug at B, either.
2687
2688Suppose further that the two development lines merge cleanly at C,
2689so no conflict resolution is required.
2690
2691Nevertheless, the code at C is broken, because the callers added
2692on the lower line of development have not been converted to the new
2693semantics introduced on the upper line of development. So if all
2694you know is that D is bad, that Z is good, and that
5162e697 2695linkgit:git-bisect[1] identifies C as the culprit, how will you
3fb00282
SP
2696figure out that the problem is due to this change in semantics?
2697
6127c086 2698When the result of a `git bisect` is a non-merge commit, you should
3fb00282
SP
2699normally be able to discover the problem by examining just that commit.
2700Developers can make this easy by breaking their changes into small
2701self-contained commits. That won't help in the case above, however,
2702because the problem isn't obvious from examination of any single
2703commit; instead, a global view of the development is required. To
2704make matters worse, the change in semantics in the problematic
2705function may be just one small part of the changes in the upper
2706line of development.
2707
2708On the other hand, if instead of merging at C you had rebased the
2709history between Z to B on top of A, you would have gotten this
2710linear history:
2711
2712................................................................
2713 ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D*
2714................................................................
2715
2716Bisecting between Z and D* would hit a single culprit commit Y*,
2717and understanding why Y* was broken would probably be easier.
2718
2719Partly for this reason, many experienced git users, even when
2720working on an otherwise merge-heavy project, keep the history
2721linear by rebasing against the latest upstream version before
2722publishing.
2723
e34caace 2724[[advanced-branch-management]]
b181d57f
BF
2725Advanced branch management
2726==========================
4c63ff45 2727
e34caace 2728[[fetching-individual-branches]]
b181d57f
BF
2729Fetching individual branches
2730----------------------------
2731
5162e697 2732Instead of using linkgit:git-remote[1], you can also choose just
b181d57f
BF
2733to update one branch at a time, and to store it locally under an
2734arbitrary name:
2735
2736-------------------------------------------------
2737$ git fetch origin todo:my-todo-work
2738-------------------------------------------------
2739
2740The first argument, "origin", just tells git to fetch from the
2741repository you originally cloned from. The second argument tells git
2742to fetch the branch named "todo" from the remote repository, and to
2743store it locally under the name refs/heads/my-todo-work.
2744
2745You can also fetch branches from other repositories; so
2746
2747-------------------------------------------------
2748$ git fetch git://example.com/proj.git master:example-master
2749-------------------------------------------------
2750
2751will create a new branch named "example-master" and store in it the
2752branch named "master" from the repository at the given URL. If you
2753already have a branch named example-master, it will attempt to
59723040
BF
2754<<fast-forwards,fast-forward>> to the commit given by example.com's
2755master branch. In more detail:
b181d57f 2756
59723040
BF
2757[[fetch-fast-forwards]]
2758git fetch and fast-forwards
2759---------------------------
b181d57f 2760
6127c086 2761In the previous example, when updating an existing branch, "git fetch"
7a7d4ef6 2762checks to make sure that the most recent commit on the remote
b181d57f
BF
2763branch is a descendant of the most recent commit on your copy of the
2764branch before updating your copy of the branch to point at the new
a75d7b54 2765commit. Git calls this process a <<fast-forwards,fast-forward>>.
b181d57f 2766
a75d7b54 2767A fast-forward looks something like this:
b181d57f 2768
1dc71a91 2769................................................
b181d57f
BF
2770 o--o--o--o <-- old head of the branch
2771 \
2772 o--o--o <-- new head of the branch
1dc71a91 2773................................................
b181d57f
BF
2774
2775
2776In some cases it is possible that the new head will *not* actually be
2777a descendant of the old head. For example, the developer may have
2778realized she made a serious mistake, and decided to backtrack,
2779resulting in a situation like:
2780
1dc71a91 2781................................................
b181d57f
BF
2782 o--o--o--o--a--b <-- old head of the branch
2783 \
2784 o--o--o <-- new head of the branch
1dc71a91 2785................................................
b181d57f 2786
6127c086 2787In this case, "git fetch" will fail, and print out a warning.
b181d57f
BF
2788
2789In that case, you can still force git to update to the new head, as
2790described in the following section. However, note that in the
2791situation above this may mean losing the commits labeled "a" and "b",
2792unless you've already created a reference of your own pointing to
2793them.
2794
e34caace 2795[[forcing-fetch]]
6127c086 2796Forcing git fetch to do non-fast-forward updates
b181d57f
BF
2797------------------------------------------------
2798
2799If git fetch fails because the new head of a branch is not a
2800descendant of the old head, you may force the update with:
2801
2802-------------------------------------------------
2803$ git fetch git://example.com/proj.git +master:refs/remotes/example/master
2804-------------------------------------------------
2805
c64415e2
BF
2806Note the addition of the "+" sign. Alternatively, you can use the "-f"
2807flag to force updates of all the fetched branches, as in:
2808
2809-------------------------------------------------
2810$ git fetch -f origin
2811-------------------------------------------------
2812
2813Be aware that commits that the old version of example/master pointed at
2814may be lost, as we saw in the previous section.
b181d57f 2815
e34caace 2816[[remote-branch-configuration]]
29b9a66f
MM
2817Configuring remote-tracking branches
2818------------------------------------
b181d57f
BF
2819
2820We saw above that "origin" is just a shortcut to refer to the
79c96c57 2821repository that you originally cloned from. This information is
b181d57f 2822stored in git configuration variables, which you can see using
5162e697 2823linkgit:git-config[1]:
b181d57f
BF
2824
2825-------------------------------------------------
9d13bda3 2826$ git config -l
b181d57f
BF
2827core.repositoryformatversion=0
2828core.filemode=true
2829core.logallrefupdates=true
2830remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2831remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2832branch.master.remote=origin
2833branch.master.merge=refs/heads/master
2834-------------------------------------------------
2835
2836If there are other repositories that you also use frequently, you can
2837create similar configuration options to save typing; for example,
2838after
2839
2840-------------------------------------------------
9d13bda3 2841$ git config remote.example.url git://example.com/proj.git
b181d57f
BF
2842-------------------------------------------------
2843
2844then the following two commands will do the same thing:
2845
2846-------------------------------------------------
2847$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2848$ git fetch example master:refs/remotes/example/master
2849-------------------------------------------------
2850
2851Even better, if you add one more option:
2852
2853-------------------------------------------------
9d13bda3 2854$ git config remote.example.fetch master:refs/remotes/example/master
b181d57f
BF
2855-------------------------------------------------
2856
2857then the following commands will all do the same thing:
2858
2859-------------------------------------------------
52c80037
BF
2860$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2861$ git fetch example master:refs/remotes/example/master
b181d57f
BF
2862$ git fetch example
2863-------------------------------------------------
2864
2865You can also add a "+" to force the update each time:
2866
2867-------------------------------------------------
9d13bda3 2868$ git config remote.example.fetch +master:ref/remotes/example/master
b181d57f
BF
2869-------------------------------------------------
2870
2871Don't do this unless you're sure you won't mind "git fetch" possibly
4f80b27d 2872throwing away commits on 'example/master'.
b181d57f
BF
2873
2874Also note that all of the above configuration can be performed by
2875directly editing the file .git/config instead of using
5162e697 2876linkgit:git-config[1].
b181d57f 2877
5162e697 2878See linkgit:git-config[1] for more details on the configuration
b181d57f 2879options mentioned above.
d19fbc3c 2880
d19fbc3c 2881
036f8199
BF
2882[[git-concepts]]
2883Git concepts
2884============
d19fbc3c 2885
036f8199
BF
2886Git is built on a small number of simple but powerful ideas. While it
2887is possible to get things done without understanding them, you will find
2888git much more intuitive if you do.
2889
2890We start with the most important, the <<def_object_database,object
2891database>> and the <<def_index,index>>.
b181d57f 2892
e34caace 2893[[the-object-database]]
b181d57f
BF
2894The Object Database
2895-------------------
2896
1bbf1c79
BF
2897
2898We already saw in <<understanding-commits>> that all commits are stored
2899under a 40-digit "object name". In fact, all the information needed to
2900represent the history of a project is stored in objects with such names.
a6e5ef7d
FC
2901In each case the name is calculated by taking the SHA-1 hash of the
2902contents of the object. The SHA-1 hash is a cryptographic hash function.
1bbf1c79
BF
2903What that means to us is that it is impossible to find two different
2904objects with the same name. This has a number of advantages; among
2905others:
2906
2907- Git can quickly determine whether two objects are identical or not,
2908 just by comparing names.
06ada152 2909- Since object names are computed the same way in every repository, the
1bbf1c79
BF
2910 same content stored in two repositories will always be stored under
2911 the same name.
2912- Git can detect errors when it reads an object, by checking that the
a6e5ef7d 2913 object's name is still the SHA-1 hash of its contents.
1bbf1c79
BF
2914
2915(See <<object-details>> for the details of the object formatting and
a6e5ef7d 2916SHA-1 calculation.)
1bbf1c79
BF
2917
2918There are four different types of objects: "blob", "tree", "commit", and
2919"tag".
2920
2921- A <<def_blob_object,"blob" object>> is used to store file data.
843c81dc 2922- A <<def_tree_object,"tree" object>> ties one or more
1bbf1c79
BF
2923 "blob" objects into a directory structure. In addition, a tree object
2924 can refer to other tree objects, thus creating a directory hierarchy.
2925- A <<def_commit_object,"commit" object>> ties such directory hierarchies
2ef8ac1b 2926 together into a <<def_DAG,directed acyclic graph>> of revisions--each
1bbf1c79
BF
2927 commit contains the object name of exactly one tree designating the
2928 directory hierarchy at the time of the commit. In addition, a commit
2929 refers to "parent" commit objects that describe the history of how we
2930 arrived at that directory hierarchy.
2931- A <<def_tag_object,"tag" object>> symbolically identifies and can be
2932 used to sign other objects. It contains the object name and type of
2933 another object, a symbolic name (of course!) and, optionally, a
2934 signature.
b181d57f 2935
b181d57f
BF
2936The object types in some more detail:
2937
513d419c
BF
2938[[commit-object]]
2939Commit Object
2940~~~~~~~~~~~~~
b181d57f 2941
1bbf1c79
BF
2942The "commit" object links a physical state of a tree with a description
2943of how we got there and why. Use the --pretty=raw option to
5162e697 2944linkgit:git-show[1] or linkgit:git-log[1] to examine your favorite
1bbf1c79
BF
2945commit:
2946
2947------------------------------------------------
2948$ git show -s --pretty=raw 2be7fcb476
2949commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4
2950tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf
2951parent 257a84d9d02e90447b149af58b271c19405edb6a
2952author Dave Watson <dwatson@mimvista.com> 1187576872 -0400
2953committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700
2954
2955 Fix misspelling of 'suppress' in docs
2956
2957 Signed-off-by: Junio C Hamano <gitster@pobox.com>
2958------------------------------------------------
2959
2960As you can see, a commit is defined by:
2961
a6e5ef7d 2962- a tree: The SHA-1 name of a tree object (as defined below), representing
1bbf1c79 2963 the contents of a directory at a certain point in time.
a6e5ef7d 2964- parent(s): The SHA-1 name of some number of commits which represent the
9e5d87d4 2965 immediately previous step(s) in the history of the project. The
1bbf1c79
BF
2966 example above has one parent; merge commits may have more than
2967 one. A commit with no parents is called a "root" commit, and
2968 represents the initial revision of a project. Each project must have
2969 at least one root. A project can also have multiple roots, though
2970 that isn't common (or necessarily a good idea).
2971- an author: The name of the person responsible for this change, together
2972 with its date.
2973- a committer: The name of the person who actually created the commit,
2974 with the date it was done. This may be different from the author, for
2975 example, if the author was someone who wrote a patch and emailed it
2976 to the person who used it to create the commit.
2977- a comment describing this commit.
2978
2979Note that a commit does not itself contain any information about what
2980actually changed; all changes are calculated by comparing the contents
2981of the tree referred to by this commit with the trees associated with
2982its parents. In particular, git does not attempt to record file renames
2983explicitly, though it can identify cases where the existence of the same
2984file data at changing paths suggests a rename. (See, for example, the
5162e697 2985-M option to linkgit:git-diff[1]).
1bbf1c79 2986
5162e697 2987A commit is usually created by linkgit:git-commit[1], which creates a
1bbf1c79
BF
2988commit whose parent is normally the current HEAD, and whose tree is
2989taken from the content currently stored in the index.
b181d57f 2990
e34caace 2991[[tree-object]]
b181d57f 2992Tree Object
971aa71f 2993~~~~~~~~~~~
b181d57f 2994
5162e697
DM
2995The ever-versatile linkgit:git-show[1] command can also be used to
2996examine tree objects, but linkgit:git-ls-tree[1] will give you more
1bbf1c79
BF
2997details:
2998
2999------------------------------------------------
3000$ git ls-tree fb3a8bdd0ce
3001100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore
3002100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap
3003100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING
3004040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation
3005100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN
3006100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL
3007100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile
3008100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README
3009...
3010------------------------------------------------
3011
3012As you can see, a tree object contains a list of entries, each with a
a6e5ef7d 3013mode, object type, SHA-1 name, and name, sorted by name. It represents
1bbf1c79
BF
3014the contents of a single directory tree.
3015
3016The object type may be a blob, representing the contents of a file, or
3017another tree, representing the contents of a subdirectory. Since trees
a6e5ef7d
FC
3018and blobs, like all other objects, are named by the SHA-1 hash of their
3019contents, two trees have the same SHA-1 name if and only if their
1bbf1c79
BF
3020contents (including, recursively, the contents of all subdirectories)
3021are identical. This allows git to quickly determine the differences
3022between two related tree objects, since it can ignore any entries with
3023identical object names.
3024
3025(Note: in the presence of submodules, trees may also have commits as
6dd14366 3026entries. See <<submodules>> for documentation.)
1bbf1c79
BF
3027
3028Note that the files all have mode 644 or 755: git actually only pays
3029attention to the executable bit.
b181d57f 3030
513d419c
BF
3031[[blob-object]]
3032Blob Object
3033~~~~~~~~~~~
b181d57f 3034
5162e697 3035You can use linkgit:git-show[1] to examine the contents of a blob; take,
1bbf1c79 3036for example, the blob in the entry for "COPYING" from the tree above:
b181d57f 3037
1bbf1c79
BF
3038------------------------------------------------
3039$ git show 6ff87c4664
3040
3041 Note that the only valid version of the GPL as far as this project
3042 is concerned is _this_ particular version of the license (ie v2, not
3043 v2.2 or v3.x or whatever), unless explicitly otherwise stated.
3044...
3045------------------------------------------------
b181d57f 3046
1bbf1c79
BF
3047A "blob" object is nothing but a binary blob of data. It doesn't refer
3048to anything else or have attributes of any kind.
3049
3050Since the blob is entirely defined by its data, if two files in a
3051directory tree (or in multiple different versions of the repository)
3052have the same contents, they will share the same blob object. The object
3053is totally independent of its location in the directory tree, and
3054renaming a file does not change the object that file is associated with.
3055
3056Note that any tree or blob object can be examined using
5162e697 3057linkgit:git-show[1] with the <revision>:<path> syntax. This can
1bbf1c79
BF
3058sometimes be useful for browsing the contents of a tree that is not
3059currently checked out.
b181d57f 3060
e34caace 3061[[trust]]
b181d57f 3062Trust
971aa71f 3063~~~~~
b181d57f 3064
a6e5ef7d 3065If you receive the SHA-1 name of a blob from one source, and its contents
1bbf1c79 3066from another (possibly untrusted) source, you can still trust that those
a6e5ef7d
FC
3067contents are correct as long as the SHA-1 name agrees. This is because
3068the SHA-1 is designed so that it is infeasible to find different contents
1bbf1c79 3069that produce the same hash.
b181d57f 3070
a6e5ef7d 3071Similarly, you need only trust the SHA-1 name of a top-level tree object
1bbf1c79 3072to trust the contents of the entire directory that it refers to, and if
a6e5ef7d 3073you receive the SHA-1 name of a commit from a trusted source, then you
1bbf1c79
BF
3074can easily verify the entire history of commits reachable through
3075parents of that commit, and all of those contents of the trees referred
3076to by those commits.
b181d57f
BF
3077
3078So to introduce some real trust in the system, the only thing you need
3079to do is to digitally sign just 'one' special note, which includes the
3080name of a top-level commit. Your digital signature shows others
3081that you trust that commit, and the immutability of the history of
3082commits tells others that they can trust the whole history.
3083
3084In other words, you can easily validate a whole archive by just
a6e5ef7d 3085sending out a single email that tells the people the name (SHA-1 hash)
b181d57f
BF
3086of the top commit, and digitally sign that email using something
3087like GPG/PGP.
3088
3089To assist in this, git also provides the tag object...
3090
e34caace 3091[[tag-object]]
b181d57f 3092Tag Object
971aa71f 3093~~~~~~~~~~
b181d57f 3094
1bbf1c79
BF
3095A tag object contains an object, object type, tag name, the name of the
3096person ("tagger") who created the tag, and a message, which may contain
843c81dc 3097a signature, as can be seen using linkgit:git-cat-file[1]:
b181d57f 3098
1bbf1c79
BF
3099------------------------------------------------
3100$ git cat-file tag v1.5.0
3101object 437b1b20df4b356c9342dac8d38849f24ef44f27
3102type commit
3103tag v1.5.0
3104tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000
3105
3106GIT 1.5.0
3107-----BEGIN PGP SIGNATURE-----
3108Version: GnuPG v1.4.6 (GNU/Linux)
3109
3110iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui
3111nLE/L9aUXdWeTFPron96DLA=
3112=2E+0
3113-----END PGP SIGNATURE-----
3114------------------------------------------------
b181d57f 3115
5162e697
DM
3116See the linkgit:git-tag[1] command to learn how to create and verify tag
3117objects. (Note that linkgit:git-tag[1] can also be used to create
1bbf1c79 3118"lightweight tags", which are not tag objects at all, but just simple
fc74ecc1 3119references whose names begin with "refs/tags/").
b181d57f 3120
09eff7b0
BF
3121[[pack-files]]
3122How git stores objects efficiently: pack files
3123~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3124
9644ffdd 3125Newly created objects are initially created in a file named after the
a6e5ef7d 3126object's SHA-1 hash (stored in .git/objects).
09eff7b0
BF
3127
3128Unfortunately this system becomes inefficient once a project has a
3129lot of objects. Try this on an old project:
3130
3131------------------------------------------------
3132$ git count-objects
31336930 objects, 47620 kilobytes
3134------------------------------------------------
3135
3136The first number is the number of objects which are kept in
3137individual files. The second is the amount of space taken up by
3138those "loose" objects.
3139
3140You can save space and make git faster by moving these loose objects in
3141to a "pack file", which stores a group of objects in an efficient
3142compressed format; the details of how pack files are formatted can be
3143found in link:technical/pack-format.txt[technical/pack-format.txt].
3144
3145To put the loose objects into a pack, just run git repack:
3146
3147------------------------------------------------
3148$ git repack
3149Generating pack...
3150Done counting 6020 objects.
3151Deltifying 6020 objects.
3152 100% (6020/6020) done
3153Writing 6020 objects.
3154 100% (6020/6020) done
3155Total 6020, written 6020 (delta 4070), reused 0 (delta 0)
3156Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.
3157------------------------------------------------
3158
3159You can then run
3160
3161------------------------------------------------
3162$ git prune
3163------------------------------------------------
3164
3165to remove any of the "loose" objects that are now contained in the
3166pack. This will also remove any unreferenced objects (which may be
6127c086 3167created when, for example, you use "git reset" to remove a commit).
09eff7b0
BF
3168You can verify that the loose objects are gone by looking at the
3169.git/objects directory or by running
3170
3171------------------------------------------------
3172$ git count-objects
31730 objects, 0 kilobytes
3174------------------------------------------------
3175
3176Although the object files are gone, any commands that refer to those
3177objects will work exactly as they did before.
3178
5162e697 3179The linkgit:git-gc[1] command performs packing, pruning, and more for
09eff7b0
BF
3180you, so is normally the only high-level command you need.
3181
3182[[dangling-objects]]
3183Dangling objects
3184~~~~~~~~~~~~~~~~
3185
5162e697 3186The linkgit:git-fsck[1] command will sometimes complain about dangling
09eff7b0
BF
3187objects. They are not a problem.
3188
3189The most common cause of dangling objects is that you've rebased a
3190branch, or you have pulled from somebody else who rebased a branch--see
3191<<cleaning-up-history>>. In that case, the old head of the original
3192branch still exists, as does everything it pointed to. The branch
3193pointer itself just doesn't, since you replaced it with another one.
3194
3195There are also other situations that cause dangling objects. For
6127c086 3196example, a "dangling blob" may arise because you did a "git add" of a
09eff7b0
BF
3197file, but then, before you actually committed it and made it part of the
3198bigger picture, you changed something else in that file and committed
2ef8ac1b 3199that *updated* thing--the old state that you added originally ends up
09eff7b0
BF
3200not being pointed to by any commit or tree, so it's now a dangling blob
3201object.
3202
3203Similarly, when the "recursive" merge strategy runs, and finds that
3204there are criss-cross merges and thus more than one merge base (which is
3205fairly unusual, but it does happen), it will generate one temporary
3206midway tree (or possibly even more, if you had lots of criss-crossing
3207merges and more than two merge bases) as a temporary internal merge
3208base, and again, those are real objects, but the end result will not end
3209up pointing to them, so they end up "dangling" in your repository.
3210
3211Generally, dangling objects aren't anything to worry about. They can
3212even be very useful: if you screw something up, the dangling objects can
3213be how you recover your old tree (say, you did a rebase, and realized
2ef8ac1b 3214that you really didn't want to--you can look at what dangling objects
09eff7b0
BF
3215you have, and decide to reset your head to some old dangling state).
3216
3217For commits, you can just use:
3218
3219------------------------------------------------
3220$ gitk <dangling-commit-sha-goes-here> --not --all
3221------------------------------------------------
3222
3223This asks for all the history reachable from the given commit but not
3224from any branch, tag, or other reference. If you decide it's something
3225you want, you can always create a new reference to it, e.g.,
3226
3227------------------------------------------------
3228$ git branch recovered-branch <dangling-commit-sha-goes-here>
3229------------------------------------------------
3230
3231For blobs and trees, you can't do the same, but you can still examine
3232them. You can just do
3233
3234------------------------------------------------
3235$ git show <dangling-blob/tree-sha-goes-here>
3236------------------------------------------------
3237
3238to show what the contents of the blob were (or, for a tree, basically
3239what the "ls" for that directory was), and that may give you some idea
3240of what the operation was that left that dangling object.
3241
3242Usually, dangling blobs and trees aren't very interesting. They're
3243almost always the result of either being a half-way mergebase (the blob
3244will often even have the conflict markers from a merge in it, if you
3245have had conflicting merges that you fixed up by hand), or simply
6127c086 3246because you interrupted a "git fetch" with ^C or something like that,
09eff7b0
BF
3247leaving _some_ of the new objects in the object database, but just
3248dangling and useless.
3249
3250Anyway, once you are sure that you're not interested in any dangling
3251state, you can just prune all unreachable objects:
3252
3253------------------------------------------------
3254$ git prune
3255------------------------------------------------
3256
3257and they'll be gone. But you should only run "git prune" on a quiescent
2ef8ac1b 3258repository--it's kind of like doing a filesystem fsck recovery: you
09eff7b0
BF
3259don't want to do that while the filesystem is mounted.
3260
6127c086
FC
3261(The same is true of "git fsck" itself, btw, but since
3262`git fsck` never actually *changes* the repository, it just reports
3263on what it found, `git fsck` itself is never 'dangerous' to run.
09eff7b0
BF
3264Running it while somebody is actually changing the repository can cause
3265confusing and scary messages, but it won't actually do anything bad. In
3266contrast, running "git prune" while somebody is actively changing the
3267repository is a *BAD* idea).
b181d57f 3268
1cdade2c
BF
3269[[recovering-from-repository-corruption]]
3270Recovering from repository corruption
3271~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3272
3273By design, git treats data trusted to it with caution. However, even in
3274the absence of bugs in git itself, it is still possible that hardware or
3275operating system errors could corrupt data.
3276
3277The first defense against such problems is backups. You can back up a
3278git directory using clone, or just using cp, tar, or any other backup
3279mechanism.
3280
3281As a last resort, you can search for the corrupted objects and attempt
3282to replace them by hand. Back up your repository before attempting this
3283in case you corrupt things even more in the process.
3284
3285We'll assume that the problem is a single missing or corrupted blob,
9e5d87d4 3286which is sometimes a solvable problem. (Recovering missing trees and
1cdade2c
BF
3287especially commits is *much* harder).
3288
3289Before starting, verify that there is corruption, and figure out where
5162e697 3290it is with linkgit:git-fsck[1]; this may be time-consuming.
1cdade2c
BF
3291
3292Assume the output looks like this:
3293
3294------------------------------------------------
b1889c36 3295$ git fsck --full
1cdade2c
BF
3296broken link from t