man-pages/man5/core.5

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.TH CORE 5 2006-04-03 "Linux 2.6.16" "Linux Programmer's Manual"
.SH NAME
core \- core dump file
.SH DESCRIPTION
The default action of certain signals is to cause a process to terminate 
and produce a
.IR "core dump file" ,
a disk file containing an image of the process's memory at 
the time of termination.
A list of the signals which cause a process to dump core can be found in
.BR signal (7).

A process can set its soft
.BR RLIMIT_CORE
resource limit to place an upper limit on the size of the core dump file 
that will be produced if it receives a "core dump" signal; see
.BR getrlimit (2)
for details.

There are various circumstances in which a core dump file is 
not produced:
.IP *
The process does not have permission to write a file named
.I core
in the current directory, either because the current directory
is non-writable, or a file called
.I core
exists and is non-writable.
.IP *
The directory prefix of the
.I core_pattern
file (see below) refers to non-writable directory.
.IP *
The 
.I core_pattern
file
names a directory or an existing, non-writable file.
.IP *
.B RLIMIT_CORE
or 
.B RLIMIT_FSIZE
resource limits for a process are set to zero (see
.BR getrlimit (2)).
.IP *
The binary being executed by the process does not have read 
permission enabled.
.IP *
The process is executing a set-user-ID (set-group-ID) program
that is owned by a user (group) other than the real user (group) 
ID of the process.
(However, see the description of the
.BR prctl (2)
.B PR_SET_DUMPABLE
operation, and the description of the
.I /proc/sys/fs/suid_dumpable
file in
.BR proc (5).)
.SS Naming of core dump files
By default, a core dump file is named 
.IR core ,
but this name can be changed by setting the value of the file 
.IR /proc/sys/kernel/core_pattern ;
see
.BR proc (5)
for details.

By default, a core dump file is named 
.IR core ,
but the 
.I /proc/sys/kernel/core_pattern
file
(new in Linux 2.5) 
can be set to define a template that is used to name core dump files.
The template can contain % specifiers which are substituted
by the following values when a core file is created:
.nf
    
  %%  A single % character
  %p  PID of dumped process
  %u  real UID of dumped process
  %g  real GID of dumped process
  %s  number of signal causing dump
  %t  time of dump (seconds since 0:00h, 1 Jan 1970)
  %h  hostname (same as 'nodename' returned by \fBuname\fP(2))
  %e  executable filename
    
.fi
A single % at the end of the template is dropped from the 
core filename, as is the combination of a % followed by any 
character other than those listed above.
All other characters in the template become a literal
part of the core filename.
The template may include `/' characters, which are interpreted
as delimiters for directory names.
The maximum size of the resulting core filename is 64 bytes.
The default value in this file is "core".
For backward compatibility, if
.I /proc/sys/kernel/core_pattern
does not include "%p" and
.I /proc/sys/kernel/core_uses_pid
(see below)
is non-zero, then .PID will be appended to the core filename.

Linux 2.4 does not provide
.IR /proc/sys/kernel/core_pattern ,
but does provide a more primitive method of controlling
the name of the core dump file.
If the
.I /proc/sys/kernel/core_uses_pid
file contains the value 0, then a core dump file is simply named
.IR core .
If this file contains a non-zero value, then the core dump file includes
the process ID in a name of the form
.IR core.PID .
.SH NOTES
The 
.BR gdb (1)
.I gcore
command can be used to obtain a core dump of a running process.
.SH SEE ALSO
.BR gdb (1),
.BR getrlimit (2),
.BR prctl (2),
.BR sigaction (2),
.BR elf (5),
.BR proc (5),
.BR signal (7)