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NAME
core - core dump file
DESCRIPTION
The default action of certain signals is to cause a process to termi‐
nate 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 pro‐
duced:
* 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 per‐
mission 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).)
Naming of core dump files
By default, a core dump file is named core, but the /proc/sys/ker‐
nel/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 con‐
tain % 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 file‐
name, as is the combination of a % followed by any character other than
those listed above. All other characters in the template become a lit‐
eral part of the core filename. The template may include ’/’ charac‐
ters, 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/ker‐
nel/core_uses_pid (see below) is non-zero, 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/ker‐
nel/core_uses_pid file contains the value 0, then a core dump file is
simply named core. If this file contains a non-zero value, then the
core dump file includes the process ID in a name of the form core.PID.
NOTES
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 implementa‐
tion, where each thread of a process has a different PID.)
gdb(1), getrlimit(2), prctl(2), sigaction(2), elf(5), proc(5),
pthreads(7), signal(7)