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Updated: July 2014

git-bisect (1)


git-bisect - Find by binary search the change that introduced a bug


git bisect <subcommand> <options>


Git Manual                                          GIT-BISECT(1)

     git-bisect - Find by binary search the change that
     introduced a bug

     git bisect <subcommand> <options>

     The command takes various subcommands, and different options
     depending on the subcommand:

         git bisect help
         git bisect start [--no-checkout] [<bad> [<good>...]] [--] [<paths>...]
         git bisect bad [<rev>]
         git bisect good [<rev>...]
         git bisect skip [(<rev>|<range>)...]
         git bisect reset [<commit>]
         git bisect visualize
         git bisect replay <logfile>
         git bisect log
         git bisect run <cmd>...

     This command uses git rev-list --bisect to help drive the
     binary search process to find which change introduced a bug,
     given an old "good" commit object name and a later "bad"
     commit object name.

  Getting help
     Use "git bisect" to get a short usage description, and "git
     bisect help" or "git bisect -h" to get a long usage

  Basic bisect commands: start, bad, good
     Using the Linux kernel tree as an example, basic use of the
     bisect command is as follows:

         $ git bisect start
         $ git bisect bad                 # Current version is bad
         $ git bisect good v2.6.13-rc2    # v2.6.13-rc2 was the last version
                                          # tested that was good

     When you have specified at least one bad and one good
     version, the command bisects the revision tree and outputs
     something similar to the following:

         Bisecting: 675 revisions left to test after this

     The state in the middle of the set of revisions is then
     checked out. You would now compile that kernel and boot it.

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Git Manual                                          GIT-BISECT(1)

     If the booted kernel works correctly, you would then issue
     the following command:

         $ git bisect good                       # this one is good

     The output of this command would be something similar to the

         Bisecting: 337 revisions left to test after this

     You keep repeating this process, compiling the tree, testing
     it, and depending on whether it is good or bad issuing the
     command "git bisect good" or "git bisect bad" to ask for the
     next bisection.

     Eventually there will be no more revisions left to bisect,
     and you will have been left with the first bad kernel
     revision in "refs/bisect/bad".

  Bisect reset
     After a bisect session, to clean up the bisection state and
     return to the original HEAD, issue the following command:

         $ git bisect reset

     By default, this will return your tree to the commit that
     was checked out before git bisect start. (A new git bisect
     start will also do that, as it cleans up the old bisection

     With an optional argument, you can return to a different
     commit instead:

         $ git bisect reset <commit>

     For example, git bisect reset HEAD will leave you on the
     current bisection commit and avoid switching commits at all,
     while git bisect reset bisect/bad will check out the first
     bad revision.

  Bisect visualize
     To see the currently remaining suspects in gitk, issue the
     following command during the bisection process:

         $ git bisect visualize

     view may also be used as a synonym for visualize.

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Git Manual                                          GIT-BISECT(1)

     If the DISPLAY environment variable is not set, git log is
     used instead. You can also give command line options such as
     -p and --stat.

         $ git bisect view --stat

  Bisect log and bisect replay
     After having marked revisions as good or bad, issue the
     following command to show what has been done so far:

         $ git bisect log

     If you discover that you made a mistake in specifying the
     status of a revision, you can save the output of this
     command to a file, edit it to remove the incorrect entries,
     and then issue the following commands to return to a
     corrected state:

         $ git bisect reset
         $ git bisect replay that-file

  Avoiding testing a commit
     If, in the middle of a bisect session, you know that the
     next suggested revision is not a good one to test (e.g. the
     change the commit introduces is known not to work in your
     environment and you know it does not have anything to do
     with the bug you are chasing), you may want to find a nearby
     commit and try that instead.

     For example:

         $ git bisect good/bad                   # previous round was good or bad.
         Bisecting: 337 revisions left to test after this
         $ git bisect visualize                  # oops, that is uninteresting.
         $ git reset --hard HEAD~3               # try 3 revisions before what
                                                 # was suggested

     Then compile and test the chosen revision, and afterwards
     mark the revision as good or bad in the usual manner.

  Bisect skip
     Instead of choosing by yourself a nearby commit, you can ask
     git to do it for you by issuing the command:

         $ git bisect skip                 # Current version cannot be tested

     But git may eventually be unable to tell the first bad

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Git Manual                                          GIT-BISECT(1)

     commit among a bad commit and one or more skipped commits.

     You can even skip a range of commits, instead of just one
     commit, using the "<commit1>..<commit2>" notation. For

         $ git bisect skip v2.5..v2.6

     This tells the bisect process that no commit after v2.5, up
     to and including v2.6, should be tested.

     Note that if you also want to skip the first commit of the
     range you would issue the command:

         $ git bisect skip v2.5 v2.5..v2.6

     This tells the bisect process that the commits between v2.5
     included and v2.6 included should be skipped.

  Cutting down bisection by giving more parameters to bisect
     You can further cut down the number of trials, if you know
     what part of the tree is involved in the problem you are
     tracking down, by specifying path parameters when issuing
     the bisect start command:

         $ git bisect start -- arch/i386 include/asm-i386

     If you know beforehand more than one good commit, you can
     narrow the bisect space down by specifying all of the good
     commits immediately after the bad commit when issuing the
     bisect start command:

         $ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --
                            # v2.6.20-rc6 is bad
                            # v2.6.20-rc4 and v2.6.20-rc1 are good

  Bisect run
     If you have a script that can tell if the current source
     code is good or bad, you can bisect by issuing the command:

         $ git bisect run my_script arguments

     Note that the script (my_script in the above example) should
     exit with code 0 if the current source code is good, and
     exit with a code between 1 and 127 (inclusive), except 125,
     if the current source code is bad.

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Git Manual                                          GIT-BISECT(1)

     Any other exit code will abort the bisect process. It should
     be noted that a program that terminates via "exit(-1)"
     leaves $? = 255, (see the exit(3) manual page), as the value
     is chopped with "& 0377".

     The special exit code 125 should be used when the current
     source code cannot be tested. If the script exits with this
     code, the current revision will be skipped (see git bisect
     skip above). 125 was chosen as the highest sensible value to
     use for this purpose, because 126 and 127 are used by POSIX
     shells to signal specific error status (127 is for command
     not found, 126 is for command found but not
     executable---these details do not matter, as they are normal
     errors in the script, as far as "bisect run" is concerned).

     You may often find that during a bisect session you want to
     have temporary modifications (e.g. s/#define DEBUG 0/#define
     DEBUG 1/ in a header file, or "revision that does not have
     this commit needs this patch applied to work around another
     problem this bisection is not interested in") applied to the
     revision being tested.

     To cope with such a situation, after the inner git bisect
     finds the next revision to test, the script can apply the
     patch before compiling, run the real test, and afterwards
     decide if the revision (possibly with the needed patch)
     passed the test and then rewind the tree to the pristine
     state. Finally the script should exit with the status of the
     real test to let the "git bisect run" command loop determine
     the eventual outcome of the bisect session.

         Do not checkout the new working tree at each iteration
         of the bisection process. Instead just update a special
         reference named BISECT_HEAD to make it point to the
         commit that should be tested.

         This option may be useful when the test you would
         perform in each step does not require a checked out

         If the repository is bare, --no-checkout is assumed.

     o   Automatically bisect a broken build between v1.2 and

             $ git bisect start HEAD v1.2 --      # HEAD is bad, v1.2 is good
             $ git bisect run make                # "make" builds the app

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Git Manual                                          GIT-BISECT(1)

     o   Automatically bisect a test failure between origin and

             $ git bisect start HEAD origin --    # HEAD is bad, origin is good
             $ git bisect run make test           # "make test" builds and tests

     o   Automatically bisect a broken test case:

             $ cat ~/
             make || exit 125                     # this skips broken builds
             ~/                 # does the test case pass?
             $ git bisect start HEAD HEAD~10 --   # culprit is among the last 10
             $ git bisect run ~/

         Here we use a "" custom script. In this script,
         if "make" fails, we skip the current commit.
         "" should "exit 0" if the test case
         passes, and "exit 1" otherwise.

         It is safer if both "" and ""
         are outside the repository to prevent interactions
         between the bisect, make and test processes and the

     o   Automatically bisect with temporary modifications

             $ cat ~/

             # tweak the working tree by merging the hot-fix branch
             # and then attempt a build
             if      git merge --no-commit hot-fix &&
                     # run project specific test and report its status
                     # tell the caller this is untestable

             # undo the tweak to allow clean flipping to the next commit
             git reset --hard

             # return control
             exit $status

         This applies modifications from a hot-fix branch before

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Git Manual                                          GIT-BISECT(1)

         each test run, e.g. in case your build or test
         environment changed so that older revisions may need a
         fix which newer ones have already. (Make sure the
         hot-fix branch is based off a commit which is contained
         in all revisions which you are bisecting, so that the
         merge does not pull in too much, or use git cherry-pick
         instead of git merge.)

     o   Automatically bisect a broken test case:

             $ git bisect start HEAD HEAD~10 --   # culprit is among the last 10
             $ git bisect run sh -c "make || exit 125; ~/"

         This shows that you can do without a run script if you
         write the test on a single line.

     o   Locate a good region of the object graph in a damaged

             $ git bisect start HEAD <known-good-commit> [ <boundary-commit> ... ] --no-checkout
             $ git bisect run sh -c '
                     GOOD=$(git for-each-ref "--format=%(objectname)" refs/bisect/good-*) &&
                     git rev-list --objects BISECT_HEAD --not $GOOD >tmp.$$ &&
                     git pack-objects --stdout >/dev/null <tmp.$$
                     rm -f tmp.$$
                     test $rc = 0'

         In this case, when git bisect run finishes, bisect/bad
         will refer to a commit that has at least one parent
         whose reachable graph is fully traversable in the sense
         required by git pack objects.

     See attributes(5) for descriptions of the following

     |Availability   | developer/versioning/git |
     |Stability      | Uncommitted              |
     Fighting regressions with git bisect[1], git-blame(1).

     Part of the git(1) suite

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Git Manual                                          GIT-BISECT(1)

      1. Fighting regressions with git bisect

     This software was built from source available at  The original
     community source was downloaded from  http://git-

     Further information about this software can be found on the
     open source community website at

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