1git-bisect(1) 2============= 3 4NAME 5---- 6git-bisect - Find the change that introduced a bug by binary search 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>...] 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' option 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 42The way you use it is: 43 44------------------------------------------------ 45$ git bisect start 46$ git bisect bad # Current version is bad 47$ git bisect good v2.6.13-rc2 # v2.6.13-rc2 was the last version 48 # tested that was good 49------------------------------------------------ 50 51When you give at least one bad and one good versions, it will bisect 52the revision tree and say something like: 53 54------------------------------------------------ 55Bisecting: 675 revisions left to test after this 56------------------------------------------------ 57 58and check out the state in the middle. Now, compile that kernel, and 59boot it. Now, let's say that this booted kernel works fine, then just 60do 61 62------------------------------------------------ 63$ git bisect good # this one is good 64------------------------------------------------ 65 66which will now say 67 68------------------------------------------------ 69Bisecting: 337 revisions left to test after this 70------------------------------------------------ 71 72and you continue along, compiling that one, testing it, and depending 73on whether it is good or bad, you say "git bisect good" or "git bisect 74bad", and ask for the next bisection. 75 76Until you have no more left, and you'll have been left with the first 77bad kernel rev in "refs/bisect/bad". 78 79Bisect reset 80~~~~~~~~~~~~ 81 82Oh, and then after you want to reset to the original head, do a 83 84------------------------------------------------ 85$ git bisect reset 86------------------------------------------------ 87 88to get back to the original branch, instead of being on the bisection 89commit ("git bisect start" will do that for you too, actually: it will 90reset the bisection state). 91 92Bisect visualize 93~~~~~~~~~~~~~~~~ 94 95During the bisection process, you can say 96 97------------ 98$ git bisect visualize 99------------ 100 101to see the currently remaining suspects in `gitk`. `visualize` is a bit 102too long to type and `view` is provided as a synonym. 103 104If `DISPLAY` environment variable is not set, `git log` is used 105instead. You can even give command line options such as `-p` and 106`--stat`. 107 108------------ 109$ git bisect view --stat 110------------ 111 112Bisect log and bisect replay 113~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 114 115The good/bad input is logged, and 116 117------------ 118$ git bisect log 119------------ 120 121shows what you have done so far. You can truncate its output somewhere 122and save it in a file, and run 123 124------------ 125$ git bisect replay that-file 126------------ 127 128if you find later you made a mistake telling good/bad about a 129revision. 130 131Avoiding to test a commit 132~~~~~~~~~~~~~~~~~~~~~~~~~ 133 134If in a middle of bisect session, you know what the bisect suggested 135to try next is not a good one to test (e.g. the change the commit 136introduces is known not to work in your environment and you know it 137does not have anything to do with the bug you are chasing), you may 138want to find a near-by commit and try that instead. 139 140It goes something like this: 141 142------------ 143$ git bisect good/bad # previous round was good/bad. 144Bisecting: 337 revisions left to test after this 145$ git bisect visualize # oops, that is uninteresting. 146$ git reset --hard HEAD~3 # try 3 revs before what 147 # was suggested 148------------ 149 150Then compile and test the one you chose to try. After that, tell 151bisect what the result was as usual. 152 153Bisect skip 154~~~~~~~~~~~~ 155 156Instead of choosing by yourself a nearby commit, you may just want git 157to do it for you using: 158 159------------ 160$ git bisect skip # Current version cannot be tested 161------------ 162 163But computing the commit to test may be slower afterwards and git may 164eventually not be able to tell the first bad among a bad and one or 165more "skip"ped commits. 166 167Cutting down bisection by giving more parameters to bisect start 168~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 169 170You can further cut down the number of trials if you know what part of 171the tree is involved in the problem you are tracking down, by giving 172paths parameters when you say `bisect start`, like this: 173 174------------ 175$ git bisect start -- arch/i386 include/asm-i386 176------------ 177 178If you know beforehand more than one good commits, you can narrow the 179bisect space down without doing the whole tree checkout every time you 180give good commits. You give the bad revision immediately after `start` 181and then you give all the good revisions you have: 182 183------------ 184$ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 -- 185 # v2.6.20-rc6 is bad 186 # v2.6.20-rc4 and v2.6.20-rc1 are good 187------------ 188 189Bisect run 190~~~~~~~~~~ 191 192If you have a script that can tell if the current source code is good 193or bad, you can automatically bisect using: 194 195------------ 196$ git bisect run my_script 197------------ 198 199Note that the "run" script (`my_script` in the above example) should 200exit with code 0 in case the current source code is good. Exit with a 201code between 1 and 127 (inclusive), except 125, if the current 202source code is bad. 203 204Any other exit code will abort the automatic bisect process. (A 205program that does "exit(-1)" leaves $? = 255, see exit(3) manual page, 206the value is chopped with "& 0377".) 207 208The special exit code 125 should be used when the current source code 209cannot be tested. If the "run" script exits with this code, the current 210revision will be skipped, see `git bisect skip` above. 211 212You may often find that during bisect you want to have near-constant 213tweaks (e.g., s/#define DEBUG 0/#define DEBUG 1/ in a header file, or 214"revision that does not have this commit needs this patch applied to 215work around other problem this bisection is not interested in") 216applied to the revision being tested. 217 218To cope with such a situation, after the inner git-bisect finds the 219next revision to test, with the "run" script, you can apply that tweak 220before compiling, run the real test, and after the test decides if the 221revision (possibly with the needed tweaks) passed the test, rewind the 222tree to the pristine state. Finally the "run" script can exit with 223the status of the real test to let "git bisect run" command loop to 224know the outcome. 225 226EXAMPLES 227-------- 228 229* Automatically bisect a broken build between v1.2 and HEAD: 230+ 231------------ 232$ git bisect start HEAD v1.2 -- # HEAD is bad, v1.2 is good 233$ git bisect run make # "make" builds the app 234------------ 235 236* Automatically bisect a broken test suite: 237+ 238------------ 239$ cat ~/test.sh 240#!/bin/sh 241make || exit 125 # this "skip"s broken builds 242make test # "make test" runs the test suite 243$ git bisect start v1.3 v1.1 -- # v1.3 is bad, v1.1 is good 244$ git bisect run ~/test.sh 245------------ 246+ 247Here we use a "test.sh" custom script. In this script, if "make" 248fails, we "skip" the current commit. 249+ 250It's safer to use a custom script outside the repo to prevent 251interactions between the bisect, make and test processes and the 252script. 253+ 254And "make test" should "exit 0", if the test suite passes, and 255"exit 1" (for example) otherwise. 256 257* Automatically bisect a broken test case: 258+ 259------------ 260$ cat ~/test.sh 261#!/bin/sh 262make || exit 125 # this "skip"s broken builds 263~/check_test_case.sh # does the test case passes ? 264$ git bisect start HEAD HEAD~10 -- # culprit is among the last 10 265$ git bisect run ~/test.sh 266------------ 267+ 268Here "check_test_case.sh" should "exit 0", if the test case passes, 269and "exit 1" (for example) otherwise. 270+ 271It's safer if both "test.sh" and "check_test_case.sh" scripts are 272outside the repo to prevent interactions between the bisect, make and 273test processes and the scripts. 274 275Author 276------ 277Written by Linus Torvalds <torvalds@osdl.org> 278 279Documentation 280------------- 281Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 282 283GIT 284--- 285Part of the linkgit:git[1] suite