1git-bisect(1) 2============= 3 4NAME 5---- 6git-bisect - Find by binary search the change that introduced a bug 7 8 9SYNOPSIS 10-------- 11'git bisect' <subcommand> <options> 12 13DESCRIPTION 14----------- 15The command takes various subcommands, and different options depending 16on the subcommand: 17 18 git bisect help 19 git bisect start [<bad> [<good>...]] [--] [<paths>...] 20 git bisect bad [<rev>] 21 git bisect good [<rev>...] 22 git bisect skip [(<rev>|<range>)...] 23 git bisect reset [<branch>] 24 git bisect visualize 25 git bisect replay <logfile> 26 git bisect log 27 git bisect run <cmd>... 28 29This command uses 'git rev-list --bisect' to help drive the 30binary search process to find which change introduced a bug, given an 31old "good" commit object name and a later "bad" commit object name. 32 33Getting help 34~~~~~~~~~~~~ 35 36Use "git bisect" to get a short usage description, and "git bisect 37help" or "git bisect -h" to get a long usage description. 38 39Basic bisect commands: start, bad, good 40~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 41 42Using the Linux kernel tree as an example, basic use of the bisect 43command is as follows: 44 45------------------------------------------------ 46$ git bisect start 47$ git bisect bad # Current version is bad 48$ git bisect good v2.6.13-rc2 # v2.6.13-rc2 was the last version 49 # tested that was good 50------------------------------------------------ 51 52When you have specified at least one bad and one good version, the 53command bisects the revision tree and outputs something similar to: 54 55------------------------------------------------ 56Bisecting: 675 revisions left to test after this 57------------------------------------------------ 58 59and then checks out the state in the middle. You would now compile 60that kernel and boot it. If the booted kernel works correctly, you 61would then issue the following command: 62 63------------------------------------------------ 64$ git bisect good # this one is good 65------------------------------------------------ 66 67which would then output something similar to: 68 69------------------------------------------------ 70Bisecting: 337 revisions left to test after this 71------------------------------------------------ 72 73and you continue along, compiling that one, testing it, and depending 74on whether it is good or bad issuing the command "git bisect good" 75or "git bisect bad" to ask for the next bisection. 76 77Eventually there will be no more revisions left to bisect, and you 78will have been left with the first bad kernel revision in "refs/bisect/bad". 79 80Bisect reset 81~~~~~~~~~~~~ 82 83To return to the original head after a bisect session, you issue the 84command: 85 86------------------------------------------------ 87$ git bisect reset 88------------------------------------------------ 89 90This resets the tree to the original branch instead of being on the 91bisection commit ("git bisect start" will also do that, as it resets 92the bisection state). 93 94Bisect visualize 95~~~~~~~~~~~~~~~~ 96 97During the bisection process, you issue the command: 98 99------------ 100$ git bisect visualize 101------------ 102 103to see the currently remaining suspects in 'gitk'. `view` may also 104be used as a synonym for `visualize`. 105 106If the 'DISPLAY' environment variable is not set, 'git log' is used 107instead. You can also give command line options such as `-p` and 108`--stat`. 109 110------------ 111$ git bisect view --stat 112------------ 113 114Bisect log and bisect replay 115~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 116 117After having marked revisions as good or bad, then: 118 119------------ 120$ git bisect log 121------------ 122 123shows what you have done so far. If you discover that you made a mistake 124in specifying the status of a revision, you can save the output of this 125command to a file, edit it to remove the incorrect entries, and then issue 126the following commands to return to a corrected state: 127 128------------ 129$ git bisect reset 130$ git bisect replay that-file 131------------ 132 133Avoiding testing a commit 134~~~~~~~~~~~~~~~~~~~~~~~~~ 135 136If in the middle of a bisect session, you know that the next suggested 137revision is not a good one to test (e.g. the change the commit 138introduces is known not to work in your environment and you know it 139does not have anything to do with the bug you are chasing), you may 140want to find a nearby commit and try that instead. 141 142For example: 143 144------------ 145$ git bisect good/bad # previous round was good or bad. 146Bisecting: 337 revisions left to test after this 147$ git bisect visualize # oops, that is uninteresting. 148$ git reset --hard HEAD~3 # try 3 revisions before what 149 # was suggested 150------------ 151 152Then compile and test the chosen revision. Afterwards the revision 153is marked as good or bad in the usual manner. 154 155Bisect skip 156~~~~~~~~~~~~ 157 158Instead of choosing by yourself a nearby commit, you can ask git 159to do it for you by issuing the command: 160 161------------ 162$ git bisect skip # Current version cannot be tested 163------------ 164 165But computing the commit to test may be slower afterwards and git may 166eventually not be able to tell the first bad commit among a bad commit 167and one or more skipped commits. 168 169You can even skip a range of commits, instead of just one commit, 170using the "'<commit1>'..'<commit2>'" notation. For example: 171 172------------ 173$ git bisect skip v2.5..v2.6 174------------ 175 176would mean that no commit between `v2.5` excluded and `v2.6` included 177can be tested. 178 179Note that if you also want to skip the first commit of the range you 180would issue the command: 181 182------------ 183$ git bisect skip v2.5 v2.5..v2.6 184------------ 185 186and the commit pointed to by `v2.5` would also be skipped. 187 188Cutting down bisection by giving more parameters to bisect start 189~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 190 191You can further cut down the number of trials, if you know what part of 192the tree is involved in the problem you are tracking down, by specifying 193path parameters when issuing the `bisect start` command, like this: 194 195------------ 196$ git bisect start -- arch/i386 include/asm-i386 197------------ 198 199If you know beforehand more than one good commit, you can narrow the 200bisect space down by specifying all of the good commits immediately after 201the bad commit when issuing the `bisect start` command: 202 203------------ 204$ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 -- 205 # v2.6.20-rc6 is bad 206 # v2.6.20-rc4 and v2.6.20-rc1 are good 207------------ 208 209Bisect run 210~~~~~~~~~~ 211 212If you have a script that can tell if the current source code is good 213or bad, you can bisect by issuing the command: 214 215------------ 216$ git bisect run my_script 217------------ 218 219Note that the script (`my_script` in the above example) should 220exit with code 0 if the current source code is good, and exit with a 221code between 1 and 127 (inclusive), except 125, if the current 222source code is bad. 223 224Any other exit code will abort the bisect process. It should be noted 225that a program that terminates via "exit(-1)" leaves $? = 255, (see the 226exit(3) manual page), as the value is chopped with "& 0377". 227 228The special exit code 125 should be used when the current source code 229cannot be tested. If the script exits with this code, the current 230revision will be skipped (see `git bisect skip` above). 231 232You may often find that during a bisect session you want to have 233temporary modifications (e.g. s/#define DEBUG 0/#define DEBUG 1/ in a 234header file, or "revision that does not have this commit needs this 235patch applied to work around another problem this bisection is not 236interested in") applied to the revision being tested. 237 238To cope with such a situation, after the inner 'git bisect' finds the 239next revision to test, the script can apply the patch 240before compiling, run the real test, and afterwards decide if the 241revision (possibly with the needed patch) passed the test and then 242rewind the tree to the pristine state. Finally the script should exit 243with the status of the real test to let the "git bisect run" command loop 244determine the eventual outcome of the bisect session. 245 246EXAMPLES 247-------- 248 249* Automatically bisect a broken build between v1.2 and HEAD: 250+ 251------------ 252$ git bisect start HEAD v1.2 -- # HEAD is bad, v1.2 is good 253$ git bisect run make # "make" builds the app 254------------ 255 256* Automatically bisect a broken test suite: 257+ 258------------ 259$ cat ~/test.sh 260#!/bin/sh 261make || exit 125 # this skips broken builds 262make test # "make test" runs the test suite 263$ git bisect start v1.3 v1.1 -- # v1.3 is bad, v1.1 is good 264$ git bisect run ~/test.sh 265------------ 266+ 267Here we use a "test.sh" custom script. In this script, if "make" 268fails, we skip the current commit. 269+ 270It is safer to use a custom script outside the repository to prevent 271interactions between the bisect, make and test processes and the 272script. 273+ 274"make test" should "exit 0", if the test suite passes, and 275"exit 1" otherwise. 276 277* Automatically bisect a broken test case: 278+ 279------------ 280$ cat ~/test.sh 281#!/bin/sh 282make || exit 125 # this skips broken builds 283~/check_test_case.sh # does the test case passes ? 284$ git bisect start HEAD HEAD~10 -- # culprit is among the last 10 285$ git bisect run ~/test.sh 286------------ 287+ 288Here "check_test_case.sh" should "exit 0" if the test case passes, 289and "exit 1" otherwise. 290+ 291It is safer if both "test.sh" and "check_test_case.sh" scripts are 292outside the repository to prevent interactions between the bisect, 293make and test processes and the scripts. 294 295Author 296------ 297Written by Linus Torvalds <torvalds@osdl.org> 298 299Documentation 300------------- 301Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 302 303GIT 304--- 305Part of the linkgit:git[1] suite