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    Command:

    core

    
    
    

    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.  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-
           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
              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
              exist.
    
           *  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
              csh(1)).
    
           *  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
               %e  executable filename (without path prefix)
               %E  pathname of executable, with slashes ('/') replaced by exclama-
                   tion marks ('!') (since Linux 3.0).
               %g  (numeric) real GID of dumped process
               %h  hostname (same as nodename returned by uname(2))
               %p  PID  of  dumped  process, as seen in the PID namespace in which
                   the process resides
               %P  PID of dumped process, as seen in  the  initial  PID  namespace
                   (since Linux 3.12)
               %s  number of signal causing dump
               %t  time  of dump, expressed as seconds since the Epoch, 1970-01-01
                   00:00:00 +0000 (UTC)
               %u  (numeric) real UID of dumped process
    
           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
              bytes).
    
           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
           value.
    
           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.
    
    
    

    NOTES

           The gdb(1) gcore command can be used to obtain a core dump of a running
           process.
    
           In Linux versions up to and including 2.6.27, if a  multithreaded  pro-
           cess (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 pri-
           marily useful when employing the obsolete LinuxThreads  implementation,
           where each thread of a process has a different PID.)
    
    
    

    EXAMPLE

           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):
               argc[2]=<UID=1000>
               argc[3]=<GID=100>
               argc[4]=<sig=3>
               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
    
           int
           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]);
               chdir(cwd);
    
               /* Write output to file "core.info" in that directory */
    
               fp = fopen("core.info", "w+");
               if (fp == NULL)
                   exit(EXIT_FAILURE);
    
               /* 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;
    
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