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`. `visualize` is a bit 96too long to type and `view` is provided as a synonym. 97 98If `DISPLAY` environment variable is not set, `git log` is used 99instead. You can even give command line options such as `-p` and 100`--stat`. 101 102------------ 103$ git bisect view --stat 104------------ 105 106Bisect log and bisect replay 107~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 108 109The good/bad input is logged, and 110 111------------ 112$ git bisect log 113------------ 114 115shows what you have done so far. You can truncate its output somewhere 116and save it in a file, and run 117 118------------ 119$ git bisect replay that-file 120------------ 121 122if you find later you made a mistake telling good/bad about a 123revision. 124 125Avoiding to test a commit 126~~~~~~~~~~~~~~~~~~~~~~~~~ 127 128If in a middle of bisect session, you know what the bisect suggested 129to try next is not a good one to test (e.g. the change the commit 130introduces is known not to work in your environment and you know it 131does not have anything to do with the bug you are chasing), you may 132want to find a near-by commit and try that instead. 133 134It goes something like this: 135 136------------ 137$ git bisect good/bad # previous round was good/bad. 138Bisecting: 337 revisions left to test after this 139$ git bisect visualize # oops, that is uninteresting. 140$ git reset --hard HEAD~3 # try 3 revs before what 141 # was suggested 142------------ 143 144Then compile and test the one you chose to try. After that, tell 145bisect what the result was as usual. 146 147Bisect skip 148~~~~~~~~~~~~ 149 150Instead of choosing by yourself a nearby commit, you may just want git 151to do it for you using: 152 153------------ 154$ git bisect skip # Current version cannot be tested 155------------ 156 157But computing the commit to test may be slower afterwards and git may 158eventually not be able to tell the first bad among a bad and one or 159more "skip"ped commits. 160 161Cutting down bisection by giving more parameters to bisect start 162~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 163 164You can further cut down the number of trials if you know what part of 165the tree is involved in the problem you are tracking down, by giving 166paths parameters when you say `bisect start`, like this: 167 168------------ 169$ git bisect start -- arch/i386 include/asm-i386 170------------ 171 172If you know beforehand more than one good commits, you can narrow the 173bisect space down without doing the whole tree checkout every time you 174give good commits. You give the bad revision immediately after `start` 175and then you give all the good revisions you have: 176 177------------ 178$ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 -- 179 # v2.6.20-rc6 is bad 180 # v2.6.20-rc4 and v2.6.20-rc1 are good 181------------ 182 183Bisect run 184~~~~~~~~~~ 185 186If you have a script that can tell if the current source code is good 187or bad, you can automatically bisect using: 188 189------------ 190$ git bisect run my_script 191------------ 192 193Note that the "run" script (`my_script` in the above example) should 194exit with code 0 in case the current source code is good. Exit with a 195code between 1 and 127 (inclusive), except 125, if the current 196source code is bad. 197 198Any other exit code will abort the automatic bisect process. (A 199program that does "exit(-1)" leaves $? = 255, see exit(3) manual page, 200the value is chopped with "& 0377".) 201 202The special exit code 125 should be used when the current source code 203cannot be tested. If the "run" script exits with this code, the current 204revision will be skipped, see `git bisect skip` above. 205 206You may often find that during bisect you want to have near-constant 207tweaks (e.g., s/#define DEBUG 0/#define DEBUG 1/ in a header file, or 208"revision that does not have this commit needs this patch applied to 209work around other problem this bisection is not interested in") 210applied to the revision being tested. 211 212To cope with such a situation, after the inner git-bisect finds the 213next revision to test, with the "run" script, you can apply that tweak 214before compiling, run the real test, and after the test decides if the 215revision (possibly with the needed tweaks) passed the test, rewind the 216tree to the pristine state. Finally the "run" script can exit with 217the status of the real test to let "git bisect run" command loop to 218know the outcome. 219 220Author 221------ 222Written by Linus Torvalds <torvalds@osdl.org> 223 224Documentation 225------------- 226Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 227 228GIT 229--- 230Part of the linkgit:git[7] suite