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 master branch, instead of being in one of the 89bisection branches ("git bisect start" will do that for you too, 90actually: it will reset the bisection state, and before it does that 91it checks that you're not using some old bisection branch). 92 93Bisect visualize 94~~~~~~~~~~~~~~~~ 95 96During the bisection process, you can say 97 98------------ 99$ git bisect visualize 100------------ 101 102to see the currently remaining suspects in `gitk`. `visualize` is a bit 103too long to type and `view` is provided as a synonym. 104 105If `DISPLAY` environment variable is not set, `git log` is used 106instead. You can even give command line options such as `-p` and 107`--stat`. 108 109------------ 110$ git bisect view --stat 111------------ 112 113Bisect log and bisect replay 114~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 115 116The good/bad input is logged, and 117 118------------ 119$ git bisect log 120------------ 121 122shows what you have done so far. You can truncate its output somewhere 123and save it in a file, and run 124 125------------ 126$ git bisect replay that-file 127------------ 128 129if you find later you made a mistake telling good/bad about a 130revision. 131 132Avoiding to test a commit 133~~~~~~~~~~~~~~~~~~~~~~~~~ 134 135If in a middle of bisect session, you know what the bisect suggested 136to try next is not a good one to test (e.g. the change the commit 137introduces is known not to work in your environment and you know it 138does not have anything to do with the bug you are chasing), you may 139want to find a near-by commit and try that instead. 140 141It goes something like this: 142 143------------ 144$ git bisect good/bad # previous round was good/bad. 145Bisecting: 337 revisions left to test after this 146$ git bisect visualize # oops, that is uninteresting. 147$ git reset --hard HEAD~3 # try 3 revs before what 148 # was suggested 149------------ 150 151Then compile and test the one you chose to try. After that, tell 152bisect what the result was as usual. 153 154Bisect skip 155~~~~~~~~~~~~ 156 157Instead of choosing by yourself a nearby commit, you may just want git 158to do it for you using: 159 160------------ 161$ git bisect skip # Current version cannot be tested 162------------ 163 164But computing the commit to test may be slower afterwards and git may 165eventually not be able to tell the first bad among a bad and one or 166more "skip"ped commits. 167 168Cutting down bisection by giving more parameters to bisect start 169~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 170 171You can further cut down the number of trials if you know what part of 172the tree is involved in the problem you are tracking down, by giving 173paths parameters when you say `bisect start`, like this: 174 175------------ 176$ git bisect start -- arch/i386 include/asm-i386 177------------ 178 179If you know beforehand more than one good commits, you can narrow the 180bisect space down without doing the whole tree checkout every time you 181give good commits. You give the bad revision immediately after `start` 182and then you give all the good revisions you have: 183 184------------ 185$ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 -- 186 # v2.6.20-rc6 is bad 187 # v2.6.20-rc4 and v2.6.20-rc1 are good 188------------ 189 190Bisect run 191~~~~~~~~~~ 192 193If you have a script that can tell if the current source code is good 194or bad, you can automatically bisect using: 195 196------------ 197$ git bisect run my_script 198------------ 199 200Note that the "run" script (`my_script` in the above example) should 201exit with code 0 in case the current source code is good. Exit with a 202code between 1 and 127 (inclusive), except 125, if the current 203source code is bad. 204 205Any other exit code will abort the automatic bisect process. (A 206program that does "exit(-1)" leaves $? = 255, see exit(3) manual page, 207the value is chopped with "& 0377".) 208 209The special exit code 125 should be used when the current source code 210cannot be tested. If the "run" script exits with this code, the current 211revision will be skipped, see `git bisect skip` above. 212 213You may often find that during bisect you want to have near-constant 214tweaks (e.g., s/#define DEBUG 0/#define DEBUG 1/ in a header file, or 215"revision that does not have this commit needs this patch applied to 216work around other problem this bisection is not interested in") 217applied to the revision being tested. 218 219To cope with such a situation, after the inner git-bisect finds the 220next revision to test, with the "run" script, you can apply that tweak 221before compiling, run the real test, and after the test decides if the 222revision (possibly with the needed tweaks) passed the test, rewind the 223tree to the pristine state. Finally the "run" script can exit with 224the status of the real test to let "git bisect run" command loop to 225know the outcome. 226 227EXAMPLES 228-------- 229 230* Automatically bisect a broken build between v1.2 and HEAD: 231+ 232------------ 233$ git bisect start HEAD v1.2 -- # HEAD is bad, v1.2 is good 234$ git bisect run make # "make" builds the app 235------------ 236 237* Automatically bisect a broken test suite: 238+ 239------------ 240$ cat ~/test.sh 241#!/bin/sh 242make || exit 125 # this "skip"s broken builds 243make test # "make test" runs the test suite 244$ git bisect start v1.3 v1.1 -- # v1.3 is bad, v1.1 is good 245$ git bisect run ~/test.sh 246------------ 247+ 248Here we use a "test.sh" custom script. In this script, if "make" 249fails, we "skip" the current commit. 250+ 251It's safer to use a custom script outside the repo to prevent 252interactions between the bisect, make and test processes and the 253script. 254+ 255And "make test" should "exit 0", if the test suite passes, and 256"exit 1" (for example) otherwise. 257 258* Automatically bisect a broken test case: 259+ 260------------ 261$ cat ~/test.sh 262#!/bin/sh 263make || exit 125 # this "skip"s broken builds 264~/check_test_case.sh # does the test case passes ? 265$ git bisect start HEAD HEAD~10 -- # culprit is among the last 10 266$ git bisect run ~/test.sh 267------------ 268+ 269Here "check_test_case.sh" should "exit 0", if the test case passes, 270and "exit 1" (for example) otherwise. 271+ 272It's safer if both "test.sh" and "check_test_case.sh" scripts are 273outside the repo to prevent interactions between the bisect, make and 274test processes and the scripts. 275 276Author 277------ 278Written by Linus Torvalds <torvalds@osdl.org> 279 280Documentation 281------------- 282Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. 283 284GIT 285--- 286Part of the linkgit:git[7] suite