ac4b4965a93fd5087896e8e807f6ad28db566df7
[git/git.git] / Documentation / git-bisect.txt
1 git-bisect(1)
2 =============
3
4 NAME
5 ----
6 git-bisect - Find the change that introduced a bug
7
8
9 SYNOPSIS
10 --------
11 'git bisect' <subcommand> <options>
12
13 DESCRIPTION
14 -----------
15 The command takes various subcommands, and different options
16 depending on the subcommand:
17
18 git bisect start [<paths>...]
19 git bisect bad <rev>
20 git bisect good <rev>
21 git bisect reset [<branch>]
22 git bisect visualize
23 git bisect replay <logfile>
24 git bisect log
25
26 This command uses 'git-rev-list --bisect' option to help drive
27 the binary search process to find which change introduced a bug,
28 given an old "good" commit object name and a later "bad" commit
29 object name.
30
31 The way you use it is:
32
33 ------------------------------------------------
34 $ git bisect start
35 $ git bisect bad # Current version is bad
36 $ git bisect good v2.6.13-rc2 # v2.6.13-rc2 was the last version
37 # tested that was good
38 ------------------------------------------------
39
40 When you give at least one bad and one good versions, it will
41 bisect the revision tree and say something like:
42
43 ------------------------------------------------
44 Bisecting: 675 revisions left to test after this
45 ------------------------------------------------
46
47 and check out the state in the middle. Now, compile that kernel, and boot
48 it. Now, let's say that this booted kernel works fine, then just do
49
50 ------------------------------------------------
51 $ git bisect good # this one is good
52 ------------------------------------------------
53
54 which will now say
55
56 ------------------------------------------------
57 Bisecting: 337 revisions left to test after this
58 ------------------------------------------------
59
60 and you continue along, compiling that one, testing it, and depending on
61 whether it is good or bad, you say "git bisect good" or "git bisect bad",
62 and ask for the next bisection.
63
64 Until you have no more left, and you'll have been left with the first bad
65 kernel rev in "refs/bisect/bad".
66
67 Oh, and then after you want to reset to the original head, do a
68
69 ------------------------------------------------
70 $ git bisect reset
71 ------------------------------------------------
72
73 to get back to the master branch, instead of being in one of the bisection
74 branches ("git bisect start" will do that for you too, actually: it will
75 reset the bisection state, and before it does that it checks that you're
76 not using some old bisection branch).
77
78 During the bisection process, you can say
79
80 ------------
81 $ git bisect visualize
82 ------------
83
84 to see the currently remaining suspects in `gitk`.
85
86 The good/bad input is logged, and `git bisect
87 log` shows what you have done so far. You can truncate its
88 output somewhere and save it in a file, and run
89
90 ------------
91 $ git bisect replay that-file
92 ------------
93
94 if you find later you made a mistake telling good/bad about a
95 revision.
96
97 If in a middle of bisect session, you know what the bisect
98 suggested to try next is not a good one to test (e.g. the change
99 the commit introduces is known not to work in your environment
100 and you know it does not have anything to do with the bug you
101 are chasing), you may want to find a near-by commit and try that
102 instead. It goes something like this:
103
104 ------------
105 $ git bisect good/bad # previous round was good/bad.
106 Bisecting: 337 revisions left to test after this
107 $ git bisect visualize # oops, that is uninteresting.
108 $ git reset --hard HEAD~3 # try 3 revs before what
109 # was suggested
110 ------------
111
112 Then compile and test the one you chose to try. After that,
113 tell bisect what the result was as usual.
114
115 You can further cut down the number of trials if you know what
116 part of the tree is involved in the problem you are tracking
117 down, by giving paths parameters when you say `bisect start`,
118 like this:
119
120 ------------
121 $ git bisect start arch/i386 include/asm-i386
122 ------------
123
124
125 Author
126 ------
127 Written by Linus Torvalds <torvalds@osdl.org>
128
129 Documentation
130 -------------
131 Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
132
133 GIT
134 ---
135 Part of the gitlink:git[7] suite
136