core man page on ElementaryOS

Man page or keyword search:  
man Server   4994 pages
apropos Keyword Search (all sections)
Output format
ElementaryOS logo
[printable version]

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

       core - core dump file

       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.  This image can be
       used in a debugger (e.g., gdb(1)) to inspect the state of  the  program
       at  the	time  that it terminated.  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‐

       *  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
	  nonwritable,	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 sym‐
	  bolic 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 filesystem 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 filesystem.

       *  The  directory in which the core dump file is to be created does not

       *  The  RLIMIT_CORE  (core  file	 size)	or  RLIMIT_FSIZE  (file	 size)
	  resource  limits  for	 the process are set to zero; see getrlimit(2)
	  and the documentation	 of  the  shell's  ulimit  command  (limit  in

       *  The  binary being executed by the process does not have read permis‐
	  sion 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).)

       *  (Since Linux 3.7) The kernel was configured without the CONFIG_CORE‐
	  DUMP option.

       In  addition,  a core dump may exclude part of the address space of the
       process if the madvise(2) MADV_DONTDUMP flag was employed.

   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  (numeric) real UID of dumped process
	   %g  (numeric) real GID of dumped process
	   %s  number of signal causing dump
	   %t  time of dump, expressed as seconds since the Epoch,  1970-01-01
	       00:00:00 +0000 (UTC)
	   %h  hostname (same as nodename returned by uname(2))
	   %e  executable filename (without path prefix)
	   %E  pathname of executable, with slashes ('/') replaced by exclama‐
	       tion marks ('!').
	   %c  core file size soft resource limit of crashing  process	(since
	       Linux 2.6.24)

       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 128 bytes (64  bytes  in
       kernels before 2.6.19).	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/ker‐
       nel/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.

       Since Linux 3.6, if /proc/sys/fs/suid_dumpable  is  set	to  2  ("suid‐
       safe"),	the pattern must be either an absolute pathname (starting with
       a leading '/' character) or a pipe, as defined below.

   Piping core dumps to a program
       Since kernel  2.6.19,  Linux  supports  an  alternate  syntax  for  the
       /proc/sys/kernel/core_pattern  file.   If  the  first character of this
       file is a pipe symbol (|), then the remainder of	 the  line  is	inter‐
       preted as a program to be executed.  Instead of being written to a disk
       file, the core dump is given as standard input to  the  program.	  Note
       the following points:

       *  The program must be specified using an absolute pathname (or a path‐
	  name relative to the root directory, /), and must immediately follow
	  the '|' character.

       *  The process created to run the program runs as user and group root.

       *  Command-line	arguments  can be supplied to the program (since Linux
	  2.6.24), delimited by white space (up to a total line length of  128

       *  The  command-line  arguments	can  include  any  of the % specifiers
	  listed above.	 For example, to pass the PID of the process  that  is
	  being dumped, specify %p in an argument.

   Controlling which mappings are written to the core dump
       Since  kernel 2.6.23, the Linux-specific /proc/PID/coredump_filter file
       can be used to control which memory segments are written	 to  the  core
       dump  file  in  the event that a core dump is performed for the process
       with the corresponding process ID.

       The value in the file is a  bit	mask  of  memory  mapping  types  (see
       mmap(2)).   If  a  bit  is set in the mask, then memory mappings of the
       corresponding type are dumped; otherwise they are not dumped.  The bits
       in this file have the following meanings:

	   bit 0  Dump anonymous private mappings.
	   bit 1  Dump anonymous shared mappings.
	   bit 2  Dump file-backed private mappings.
	   bit 3  Dump file-backed shared mappings.
	   bit 4 (since Linux 2.6.24)
		  Dump ELF headers.
	   bit 5 (since Linux 2.6.28)
		  Dump private huge pages.
	   bit 6 (since Linux 2.6.28)
		  Dump shared huge pages.

       By  default,  the  following  bits  are	set:  0,  1,  4	 (if  the CON‐
       FIG_CORE_DUMP_DEFAULT_ELF_HEADERS  kernel   configuration   option   is
       enabled),  and  5.  The value of this file is displayed in hexadecimal.
       (The default value is thus displayed as 33.)

       Memory-mapped I/O pages such as frame buffer are never dumped, and vir‐
       tual  DSO  pages	 are  always dumped, regardless of the coredump_filter

       A child process created via fork(2) inherits its parent's coredump_fil‐
       ter value; the coredump_filter value is preserved across an execve(2).

       It can be useful to set coredump_filter in the parent shell before run‐
       ning a program, for example:

	   $ echo 0x7 > /proc/self/coredump_filter
	   $ ./some_program

       This file is provided only if  the  kernel  was	built  with  the  CON‐
       FIG_ELF_CORE configuration option.

       The gdb(1) gcore command can be used to obtain a core dump of a running

       In Linux versions up  to	 and  including	 2.6.27,  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 file‐
       name, unless the process ID was already included elsewhere in the file‐
       name via a %p specification in /proc/sys/kernel/core_pattern.  (This is
       primarily useful when employing the obsolete  LinuxThreads  implementa‐
       tion, where each thread of a process has a different PID.)

       The program below can be used to demonstrate the use of the pipe syntax
       in the /proc/sys/kernel/core_pattern file.  The following shell session
       demonstrates  the use of this program (compiled to create an executable
       named core_pattern_pipe_test):

	   $ cc -o core_pattern_pipe_test core_pattern_pipe_test.c
	   $ su
	   # echo "|$PWD/core_pattern_pipe_test %p UID=%u GID=%g sig=%s" > \
	   # exit
	   $ sleep 100
	   ^\			  # type control-backslash
	   Quit (core dumped)
	   $ cat
	   Total bytes in core dump: 282624

   Program source

       /* core_pattern_pipe_test.c */

       #define _GNU_SOURCE
       #include <sys/stat.h>
       #include <fcntl.h>
       #include <limits.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       #define BUF_SIZE 1024

       main(int argc, char *argv[])
	   int tot, j;
	   ssize_t nread;
	   char buf[BUF_SIZE];
	   FILE *fp;
	   char cwd[PATH_MAX];

	   /* Change our current working directory to that of the
	      crashing process */

	   snprintf(cwd, PATH_MAX, "/proc/%s/cwd", argv[1]);

	   /* Write output to file "" in that directory */

	   fp = fopen("", "w+");
	   if (fp == NULL)

	   /* Display command-line arguments given to core_pattern
	      pipe program */

	   fprintf(fp, "argc=%d\n", argc);
	   for (j = 0; j < argc; j++)
	       fprintf(fp, "argc[%d]=<%s>\n", j, argv[j]);

	   /* Count bytes in standard input (the core dump) */

	   tot = 0;
	   while ((nread = read(STDIN_FILENO, buf, BUF_SIZE)) > 0)
	       tot += nread;
	   fprintf(fp, "Total bytes in core dump: %d\n", tot);


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

       This  page  is  part of release 3.54 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

Linux				  2013-06-08			       CORE(5)

List of man pages available for ElementaryOS

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net