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

       *      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  (new  in Linux 2.5) can be set to define a tem-
       plate 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  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.

       Linux 2.4 does not provide /proc/sys/kernel/core_pattern, but does pro-
       vide 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.

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.

SEE ALSO
       gdb(1),  getrlimit(2),  prctl(2),  sigaction(2),  elf(5), proc(5), sig-
       nal(7)

Linux 2.6.16                      2006-04-03                           CORE(5)