xref: /freebsd/share/man/man5/core.5 (revision 8d20be1e22095c27faf8fe8b2f0d089739cc742e)
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32.\"     @(#)core.5	8.3 (Berkeley) 12/11/93
33.\" $FreeBSD$
34.\"
35.Dd November 22, 2012
36.Dt CORE 5
37.Os
38.Sh NAME
39.Nm core
40.Nd memory image file format
41.Sh SYNOPSIS
42.In sys/param.h
43.Sh DESCRIPTION
44A small number of signals which cause abnormal termination of a process
45also cause a record of the process's in-core state to be written
46to disk for later examination by one of the available debuggers.
47(See
48.Xr sigaction 2 . )
49This memory image is written to a file named by default
50.Nm programname.core
51in the working directory;
52provided the terminated process had write permission in the directory,
53and provided the abnormality did not cause
54a system crash.
55(In this event, the decision to save the core file is arbitrary, see
56.Xr savecore 8 . )
57.Pp
58The maximum size of a core file is limited by
59.Xr setrlimit 2 .
60Files which would be larger than the limit are not created.
61.Pp
62The name of the file is controlled via the
63.Xr sysctl 8
64variable
65.Va kern.corefile .
66The contents of this variable describes a filename to store
67the core image to.
68This filename can be absolute, or relative (which
69will resolve to the current working directory of the program
70generating it).
71.Pp
72The following format specifiers may be used in the
73.Va kern.corefile
74sysctl to insert additional information into the resulting core file
75name:
76.Bl -tag -width "1234567890" -compact -offset "12345"
77.It Em \&%H
78Machine hostname.
79.It Em \&%I
80An index starting at zero until the sysctl
81.Em debug.ncores
82is reached.
83This can be useful for limiting the number of corefiles
84generated by a particular process.
85.It Em \&%N
86process name.
87.It Em \&%P
88processes PID.
89.It Em \&%U
90process UID.
91.El
92.Pp
93The name defaults to
94.Em \&%N.core ,
95yielding the traditional
96.Fx
97behaviour.
98.Pp
99By default, a process that changes user or group credentials whether
100real or effective will not create a corefile.
101This behaviour can be
102changed to generate a core dump by setting the
103.Xr sysctl 8
104variable
105.Va kern.sugid_coredump
106to 1.
107.Pp
108Corefiles can be compressed by the kernel if the following items
109are included in the kernel configuration file:
110.Bl -tag -width "1234567890" -compact -offset "12345"
111.It options
112COMPRESS_USER_CORES
113.It devices
114gzio
115.El
116.Pp
117When COMPRESS_USER_CORES is included the following sysctls can control
118if core files will be compressed:
119.Bl -tag -width "kern.compress_user_cores_gzlevel" -compact -offset "12345"
120.It Em kern.compress_user_cores_gzlevel
121Gzip compression level.
122Defaults to -1.
123.It Em kern.compress_user_cores
124Actually compress user cores.
125Core files will have the suffix
126.Em .gz
127appended to them.
128.El
129.Sh EXAMPLES
130In order to store all core images in per-user private areas under
131.Pa /var/coredumps ,
132the following
133.Xr sysctl 8
134command can be used:
135.Pp
136.Dl sysctl kern.corefile=/var/coredumps/\&%U/\&%N.core
137.Sh SEE ALSO
138.Xr gdb 1 ,
139.Xr kgdb 1 ,
140.Xr setrlimit 2 ,
141.Xr sigaction 2 ,
142.Xr sysctl 8
143.Sh HISTORY
144A
145.Nm
146file format appeared in
147.At v6 .
148