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 start [<bad> [<good>...]] [--] [<paths>...] 19 git bisect bad [<rev>] 20 git bisect good [<rev>...] 21 git bisect skip [<rev>...] 22 git bisect reset [<branch>] 23 git bisect visualize 24 git bisect replay <logfile> 25 git bisect log 26 git bisect run <cmd>... 27 28This command uses 'git-rev-list --bisect' option to help drive the 29binary search process to find which change introduced a bug, given an 30old "good" commit object name and a later "bad" commit object name. 31 32Basic bisect commands: start, bad, good 33~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 34 35The way you use it is: 36 37------------------------------------------------ 38$ git bisect start 39$ git bisect bad # Current version is bad 40$ git bisect good v2.6.13-rc2 # v2.6.13-rc2 was the last version 41 # tested that was good 42------------------------------------------------ 43 44When you give at least one bad and one good versions, it will bisect 45the revision tree and say something like: 46 47------------------------------------------------ 48Bisecting: 675 revisions left to test after this 49------------------------------------------------ 50 51and check out the state in the middle. Now, compile that kernel, and 52boot it. Now, let's say that this booted kernel works fine, then just 53do 54 55------------------------------------------------ 56$ git bisect good # this one is good 57------------------------------------------------ 58 59which will now say 60 61------------------------------------------------ 62Bisecting: 337 revisions left to test after this 63------------------------------------------------ 64 65and you continue along, compiling that one, testing it, and depending 66on whether it is good or bad, you say "git bisect good" or "git bisect 67bad", and ask for the next bisection. 68 69Until you have no more left, and you'll have been left with the first 70bad kernel rev in "refs/bisect/bad". 71 72Bisect reset 73~~~~~~~~~~~~ 74 75Oh, and then after you want to reset to the original head, do a 76 77------------------------------------------------ 78$ git bisect reset 79------------------------------------------------ 80 81to get back to the master branch, instead of being in one of the 82bisection branches ("git bisect start" will do that for you too, 83actually: it will reset the bisection state, and before it does that 84it checks that you're not using some old bisection branch). 85 86Bisect visualize 87~~~~~~~~~~~~~~~~ 88 89During the bisection process, you can say 90 91------------ 92$ git bisect visualize 93------------ 94 95to see the currently remaining suspects in `gitk`. 96 97Bisect log and bisect replay 98~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 99 100The good/bad input is logged, and 101 102------------ 103$ git bisect log 104------------ 105 106shows what you have done so far. You can truncate its output somewhere 107and save it in a file, and run 108 109------------ 110$ git bisect replay that-file 111------------ 112 113if you find later you made a mistake telling good/bad about a 114revision. 115 116Avoiding to test a commit 117~~~~~~~~~~~~~~~~~~~~~~~~~ 118 119If in a middle of bisect session, you know what the bisect suggested 120to try next is not a good one to test (e.g. the change the commit 121introduces is known not to work in your environment and you know it 122does not have anything to do with the bug you are chasing), you may 123want to find a near-by commit and try that instead. 124 125It goes something like this: 126 127------------ 128$ git bisect good/bad # previous round was good/bad. 129Bisecting: 337 revisions left to test after this 130$ git bisect visualize # oops, that is uninteresting. 131$ git reset --hard HEAD~3 # try 3 revs before what 132 # was suggested 133------------ 134 135Then compile and test the one you chose to try. After that, tell 136bisect what the result was as usual. 137 138Bisect skip 139~~~~~~~~~~~~ 140 141Instead of choosing by yourself a nearby commit, you may just want git 142to do it for you using: 143 144------------ 145$ git bisect skip # Current version cannot be tested 146------------ 147 148But computing the commit to test may be slower afterwards and git may 149eventually not be able to tell the first bad among a bad and one or 150more "skip"ped commits. 151 152Cutting down bisection by giving more parameters to bisect start 153~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 154 155You can further cut down the number of trials if you know what part of 156the tree is involved in the problem you are tracking down, by giving 157paths parameters when you say `bisect start`, like this: 158 159------------ 160$ git bisect start -- arch/i386 include/asm-i386 161------------ 162 163If you know beforehand more than one good commits, you can narrow the 164bisect space down without doing the whole tree checkout every time you 165give good commits. You give the bad revision immediately after `start` 166and then you give all the good revisions you have: 167 168------------ 169$ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 -- 170 # v2.6.20-rc6 is bad 171 # v2.6.20-rc4 and v2.6.20-rc1 are good 172------------ 173 174Bisect run 175~~~~~~~~~~ 176 177If you have a script that can tell if the current source code is good 178or bad, you can automatically bisect using: 179 180------------ 181$ git bisect run my_script 182------------ 183 184Note that the "run" script (`my_script` in the above example) should 185exit with code 0 in case the current source code is good. Exit with a 186code between 1 and 127 (inclusive), except 125, if the current 187source code is bad. 188 189Any other exit code will abort the automatic bisect process. (A 190program that does "exit(-1)" leaves $? = 255, see exit(3) manual page, 191the value is chopped with "& 0377".) 192 193The special exit code 125 should be used when the current source code 194cannot be tested. If the "run" script exits with this code, the current 195revision will be skipped, see `git bisect skip` above. 196 197You may often find that during bisect you want to have near-constant 198tweaks (e.g., s/#define DEBUG 0/#define DEBUG 1/ in a header file, or 199"revision that does not have this commit needs this patch applied to 200work around other problem this bisection is not interested in") 201applied to the revision being tested. 202 203To cope with such a situation, after the inner git-bisect finds the 204next revision to test, with the "run" script, you can apply that tweak 205before compiling, run the real test, and after the test decides if the 206revision (possibly with the needed tweaks) passed the test, rewind the 207tree to the pristine state. Finally the "run" script can exit with 208the status of the real test to let "git bisect run" command loop to 209know the outcome. 210 211Author 212------ 213Written by Linus Torvalds <torvalds@osdl.org> 214 215Documentation 216------------- 217Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 218 219GIT 220--- 221Part of the gitlink:git[7] suite