Merge branch 'maint' of git://linux-nfs.org/~bfields/git into maint
* 'maint' of git://linux-nfs.org/~bfields/git: user-manual: recovering from corruption user-manual: clarify language about "modifying" old commits user-manual: failed push to public repository user-manual: define "branch" and "working tree" at start
This commit is contained in:
Junio C Hamano
commit
dc3e3ea3c8
@ -56,11 +56,12 @@ $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
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The initial clone may be time-consuming for a large project, but you
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will only need to clone once.
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The clone command creates a new directory named after the project
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("git" or "linux-2.6" in the examples above). After you cd into this
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The clone command creates a new directory named after the project ("git"
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or "linux-2.6" in the examples above). After you cd into this
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directory, you will see that it contains a copy of the project files,
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together with a special top-level directory named ".git", which
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contains all the information about the history of the project.
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called the <<def_working_tree,working tree>>, together with a special
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top-level directory named ".git", which contains all the information
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about the history of the project.
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[[how-to-check-out]]
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How to check out a different version of a project
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@ -71,8 +72,13 @@ of files. It stores the history as a compressed collection of
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interrelated snapshots of the project's contents. In git each such
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version is called a <<def_commit,commit>>.
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A single git repository may contain multiple branches. It keeps track
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of them by keeping a list of <<def_head,heads>> which reference the
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Those snapshots aren't necessarily all arranged in a single line from
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oldest to newest; instead, work may simultaneously proceed along
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parallel lines of development, called <def_branch,branches>>, which may
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merge and diverge.
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A single git repository can track development on multiple branches. It
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does this by keeping a list of <<def_head,heads>> which reference the
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latest commit on each branch; the gitlink:git-branch[1] command shows
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you the list of branch heads:
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@ -1410,8 +1416,8 @@ with the changes to be reverted, then you will be asked to fix
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conflicts manually, just as in the case of <<resolving-a-merge,
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resolving a merge>>.
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[[fixing-a-mistake-by-editing-history]]
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Fixing a mistake by editing history
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[[fixing-a-mistake-by-rewriting-history]]
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Fixing a mistake by rewriting history
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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If the problematic commit is the most recent commit, and you have not
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@ -1434,7 +1440,7 @@ Again, you should never do this to a commit that may already have
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been merged into another branch; use gitlink:git-revert[1] instead in
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that case.
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It is also possible to edit commits further back in the history, but
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It is also possible to replace commits further back in the history, but
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this is an advanced topic to be left for
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<<cleaning-up-history,another chapter>>.
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@ -1554,6 +1560,11 @@ This may be time-consuming. Unlike most other git operations (including
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git-gc when run without any options), it is not safe to prune while
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other git operations are in progress in the same repository.
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If gitlink:git-fsck[1] complains about sha1 mismatches or missing
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objects, you may have a much more serious problem; your best option is
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probably restoring from backups. See
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<<recovering-from-repository-corruption>> for a detailed discussion.
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[[recovering-lost-changes]]
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Recovering lost changes
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~~~~~~~~~~~~~~~~~~~~~~~
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@ -1923,15 +1934,9 @@ or just
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$ git push ssh://yourserver.com/~you/proj.git master
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-------------------------------------------------
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As with git-fetch, git-push will complain if this does not result in
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a <<fast-forwards,fast forward>>. Normally this is a sign of
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something wrong. However, if you are sure you know what you're
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doing, you may force git-push to perform the update anyway by
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proceeding the branch name by a plus sign:
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-------------------------------------------------
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$ git push ssh://yourserver.com/~you/proj.git +master
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-------------------------------------------------
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As with git-fetch, git-push will complain if this does not result in a
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<<fast-forwards,fast forward>>; see the following section for details on
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handling this case.
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Note that the target of a "push" is normally a
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<<def_bare_repository,bare>> repository. You can also push to a
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@ -1959,6 +1964,52 @@ See the explanations of the remote.<name>.url, branch.<name>.remote,
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and remote.<name>.push options in gitlink:git-config[1] for
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details.
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[[forcing-push]]
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What to do when a push fails
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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If a push would not result in a <<fast-forwards,fast forward>> of the
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remote branch, then it will fail with an error like:
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-------------------------------------------------
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error: remote 'refs/heads/master' is not an ancestor of
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local 'refs/heads/master'.
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Maybe you are not up-to-date and need to pull first?
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error: failed to push to 'ssh://yourserver.com/~you/proj.git'
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-------------------------------------------------
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This can happen, for example, if you:
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- use `git reset --hard` to remove already-published commits, or
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- use `git commit --amend` to replace already-published commits
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(as in <<fixing-a-mistake-by-rewriting-history>>), or
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- use `git rebase` to rebase any already-published commits (as
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in <<using-git-rebase>>).
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You may force git-push to perform the update anyway by preceding the
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branch name with a plus sign:
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-------------------------------------------------
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$ git push ssh://yourserver.com/~you/proj.git +master
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-------------------------------------------------
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Normally whenever a branch head in a public repository is modified, it
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is modified to point to a descendent of the commit that it pointed to
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before. By forcing a push in this situation, you break that convention.
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(See <<problems-with-rewriting-history>>.)
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Nevertheless, this is a common practice for people that need a simple
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way to publish a work-in-progress patch series, and it is an acceptable
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compromise as long as you warn other developers that this is how you
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intend to manage the branch.
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It's also possible for a push to fail in this way when other people have
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the right to push to the same repository. In that case, the correct
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solution is to retry the push after first updating your work by either a
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pull or a fetch followed by a rebase; see the
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<<setting-up-a-shared-repository,next section>> and
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link:cvs-migration.html[git for CVS users] for more.
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[[setting-up-a-shared-repository]]
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Setting up a shared repository
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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@ -2426,11 +2477,11 @@ return mywork to the state it had before you started the rebase:
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$ git rebase --abort
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-------------------------------------------------
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[[modifying-one-commit]]
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Modifying a single commit
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[[rewriting-one-commit]]
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Rewriting a single commit
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-------------------------
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We saw in <<fixing-a-mistake-by-editing-history>> that you can replace the
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We saw in <<fixing-a-mistake-by-rewriting-history>> that you can replace the
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most recent commit using
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-------------------------------------------------
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@ -2440,8 +2491,10 @@ $ git commit --amend
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which will replace the old commit by a new commit incorporating your
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changes, giving you a chance to edit the old commit message first.
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You can also use a combination of this and gitlink:git-rebase[1] to edit
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commits further back in your history. First, tag the problematic commit with
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You can also use a combination of this and gitlink:git-rebase[1] to
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replace a commit further back in your history and recreate the
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intervening changes on top of it. First, tag the problematic commit
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with
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-------------------------------------------------
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$ git tag bad mywork~5
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@ -3172,6 +3225,127 @@ confusing and scary messages, but it won't actually do anything bad. In
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contrast, running "git prune" while somebody is actively changing the
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repository is a *BAD* idea).
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[[recovering-from-repository-corruption]]
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Recovering from repository corruption
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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By design, git treats data trusted to it with caution. However, even in
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the absence of bugs in git itself, it is still possible that hardware or
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operating system errors could corrupt data.
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The first defense against such problems is backups. You can back up a
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git directory using clone, or just using cp, tar, or any other backup
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mechanism.
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As a last resort, you can search for the corrupted objects and attempt
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to replace them by hand. Back up your repository before attempting this
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in case you corrupt things even more in the process.
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We'll assume that the problem is a single missing or corrupted blob,
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which is sometimes a solveable problem. (Recovering missing trees and
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especially commits is *much* harder).
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Before starting, verify that there is corruption, and figure out where
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it is with gitlink:git-fsck[1]; this may be time-consuming.
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Assume the output looks like this:
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------------------------------------------------
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$ git-fsck --full
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broken link from tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
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to blob 4b9458b3786228369c63936db65827de3cc06200
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missing blob 4b9458b3786228369c63936db65827de3cc06200
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------------------------------------------------
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(Typically there will be some "dangling object" messages too, but they
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aren't interesting.)
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Now you know that blob 4b9458b3 is missing, and that the tree 2d9263c6
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points to it. If you could find just one copy of that missing blob
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object, possibly in some other repository, you could move it into
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.git/objects/4b/9458b3... and be done. Suppose you can't. You can
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still examine the tree that pointed to it with gitlink:git-ls-tree[1],
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which might output something like:
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------------------------------------------------
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$ git ls-tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
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100644 blob 8d14531846b95bfa3564b58ccfb7913a034323b8 .gitignore
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100644 blob ebf9bf84da0aab5ed944264a5db2a65fe3a3e883 .mailmap
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100644 blob ca442d313d86dc67e0a2e5d584b465bd382cbf5c COPYING
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...
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100644 blob 4b9458b3786228369c63936db65827de3cc06200 myfile
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...
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------------------------------------------------
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So now you know that the missing blob was the data for a file named
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"myfile". And chances are you can also identify the directory--let's
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say it's in "somedirectory". If you're lucky the missing copy might be
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the same as the copy you have checked out in your working tree at
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"somedirectory/myfile"; you can test whether that's right with
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gitlink:git-hash-object[1]:
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------------------------------------------------
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$ git hash-object -w somedirectory/myfile
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------------------------------------------------
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which will create and store a blob object with the contents of
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somedirectory/myfile, and output the sha1 of that object. if you're
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extremely lucky it might be 4b9458b3786228369c63936db65827de3cc06200, in
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which case you've guessed right, and the corruption is fixed!
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Otherwise, you need more information. How do you tell which version of
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the file has been lost?
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The easiest way to do this is with:
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------------------------------------------------
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$ git log --raw --all --full-history -- somedirectory/myfile
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------------------------------------------------
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Because you're asking for raw output, you'll now get something like
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------------------------------------------------
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commit abc
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Author:
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Date:
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...
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:100644 100644 4b9458b... newsha... M somedirectory/myfile
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commit xyz
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Author:
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Date:
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...
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:100644 100644 oldsha... 4b9458b... M somedirectory/myfile
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------------------------------------------------
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This tells you that the immediately preceding version of the file was
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"newsha", and that the immediately following version was "oldsha".
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You also know the commit messages that went with the change from oldsha
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to 4b9458b and with the change from 4b9458b to newsha.
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If you've been committing small enough changes, you may now have a good
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shot at reconstructing the contents of the in-between state 4b9458b.
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If you can do that, you can now recreate the missing object with
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------------------------------------------------
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$ git hash-object -w <recreated-file>
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------------------------------------------------
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and your repository is good again!
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(Btw, you could have ignored the fsck, and started with doing a
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------------------------------------------------
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$ git log --raw --all
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------------------------------------------------
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and just looked for the sha of the missing object (4b9458b..) in that
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whole thing. It's up to you - git does *have* a lot of information, it is
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just missing one particular blob version.
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[[the-index]]
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The index
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-----------
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@ -4381,4 +4555,7 @@ Write a chapter on using plumbing and writing scripts.
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Alternates, clone -reference, etc.
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git unpack-objects -r for recovery
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More on recovery from repository corruption. See:
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http://marc.theaimsgroup.com/?l=git&m=117263864820799&w=2
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http://marc.theaimsgroup.com/?l=git&m=117147855503798&w=2
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http://marc.theaimsgroup.com/?l=git&m=117147855503798&w=2
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