CORE(5) Linux Programmer's Manual CORE(5)

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 a file named core in the current directory, either because the current directory is non-writable, or a file called core exists and is non-writable.
  • The directory prefix of the core_pattern file (see below) refers to non-writable directory.
  • The core_pattern file names a directory or an existing, non-writable file.
  • 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 this name can be changed by setting the value of the file /proc/sys/kernel/core_pattern; see proc(5) for details.

By default, a core dump file is named core, but the /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:



    

  %%  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 non-zero, then .PID will be appended to the core filename.

Linux 2.4 does not provide /proc/sys/kernel/core_pattern, but does provide 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 non-zero 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.

gdb(1), getrlimit(2), prctl(2), sigaction(2), elf(5), proc(5), signal(7)

2006-04-03 Linux 2.6.16

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