core — core dump file
The default action of certain signals is to cause a process to terminate and produce a 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 signal(7).
A process can set its soft 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 getrlimit(2) for
details.
There are various circumstances in which a core dump file is not produced:
The process does not have permission to write the
core file. (By default the core file is called
core, and is
created in the current working directory. See below for
details on naming.) Writing the core file will fail if
the directory in which it is to be created is
non-writable, or if a file with the same name exists
and is not writable or is not a regular file (e.g., it
is a directory or a symbolic link).
A (writable, regular) file with the same name as would be used for the core dump already exists, but there is more than one hard link to that file.
The file system where the core dump file would be created is full; or has run out of inodes; or is mounted read only; or the user has reached their quota for the file system.
The directory in which the core dump file is to be created does not exist.
RLIMIT_CORE or
RLIMIT_FSIZE resource
limits for a process are set to zero (see getrlimit(2)).
The binary being executed by the process does not have read permission enabled.
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 prctl(2) PR_SET_DUMPABLE operation, and the
description of the /proc/sys/fs/suid_dumpable file in
proc(5).)
By default, a core dump file is named core, but the /proc/sys/kernel/core_pattern file (since
Linux 2.6 and 2.4.21) 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:
%% 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 uname(2)) %e executable filename
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 /proc/sys/kernel/core_pattern does not
include "%p" and /proc/sys/kernel/core_uses_pid (see
below) is nonzero, then .PID will be appended to the core
filename.
Since version 2.4, Linux has also provided a more
primitive method of controlling the name of the core dump
file. If the /proc/sys/kernel/core_uses_pid file
contains the value 0, then a core dump file is simply named
core. If this
file contains a nonzero value, then the core dump file
includes the process ID in a name of the form core.PID.
The gdb(1) gcore command can be used to
obtain a core dump of a running process.
If a multithreaded process (or, more precisely, a process
that shares its memory with another process by being created
with the CLONE_VM flag of
clone(2)) dumps core, then
the process ID is always appended to the core filename,
unless the process ID was already included elsewhere in the
filename via a %p specification in /proc/sys/kernel/core_pattern. (This is
primarily useful when employing the LinuxThreads
implementation, where each thread of a process has a
different PID.)
This page is part of release 2.79 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man-pages/.
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Copyright (c) 2006 by Michael Kerrisk <mtk.manpagesgmail.com> Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. |