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core(4)								       core(4)

NAME
       core - Format of memory image file

SYNOPSIS
       #include <sys/core.h>

DESCRIPTION
       The  system  writes out a memory image of a terminated process when any
       of various errors occur. See sigaction(2) for the list of reasons;  the
       most  common  are  memory violations, illegal instructions, bus errors,
       and user-generated quit signals. The memory image is called core and is
       written	in  the	 process's working directory (provided that it can be;
       normal access controls apply).

       The maximum size of a core file is limited.  If a process exceeds  this
       limit, any remaining data to be written to the core file is lost.

       Default	behavior  is for the system to create a file named core, over‐
       writing any other file with that name in the working directory.

       You can enable enhanced core file naming, which causes  the  system  to
       create  unique  names  for  core files. Core files are not overwritten,
       thereby preventing loss of valuable debugging information when the same
       program fails mulitiple times (and perhaps for mulitple reasons).

       When  enhanced  core  file  naming is enabled, the system produces core
       files with names in the following format:

       core.program_name.host_name.numeric_tag The literal string core.	 Up to
       sixteen	characters taken from the program name as shown by the ps com‐
       mand.  The first portion of the system's network host name, or up to 16
       characters  of the host name, taken from the part of the host name that
       precedes the first dot.	This tag is assigned to the core file to  make
       it unique among all of the core files generated by a program on a host.
       The maximum value for this tag, and thus the  maximum  number  of  core
       files  for  this	 program  and  host,  is set by a system configuration
       parameter.

	      Note the tag is not a literal version number. The system selects
	      the  first  available unique tag for the core file. For example,
	      if a program's core files have tags .0, .1, and .3,  the	system
	      uses  tag .2 for the next core file it creates for that program.
	      If the  system-configured	 limit	for  core  file	 instances  is
	      reached, the system will not create any more core files for that
	      program/host combination. By default, the system can  create  up
	      to 16 versions of a core file.

	      For   example,   the   fourth   core   file  generated  on  host
	      buggy.net.ooze.com   by	the   program	dropsy	  would	   be:
	      core.dropsy.buggy.3

       Enhanced	 core  file  naming  can be enabled at the system level or the
       program level: At the system level, you can enable enhanced  core  file
       naming  by setting the enhanced-core-name system configuration variable
       to 1 in the proc subsystem: proc:
	       enhanced-core-name = 1 At the program  level,  you  can	enable
       enhanced	 core  file naming by calling the uswitch system call with the
       USW_CORE flag set.  See the EXAMPLE section.

       The system manager can limit the number of unique  core	file  versions
       that a program can create on a specific host system by setting the sys‐
       tem configuration variable enhanced-core-max-versions  to  the  desired
       value: proc:
	       enhanced-core-name = 1
	       enhanced-core-max-versions = 8 The miminum value is 1, the max‐
       imum is 99,999, and the default is 16.

EXAMPLE
       The following example shows a code fragment that calls the uswitch sys‐
       tem  call  with	the  USW_CORE  flag  set: #include <signal.h> #include
       <sys/uswitch.h>

       /*
	* Request enhanced core file naming for
	* this process then create a core file.
	*/ main() {
	       long uval = uswitch(USC_GET, 0);
	       uval = uswitch(USC_SET, uval | USW_CORE);
	       if (uval < 0) {
		      perror("uswitch");
		      exit(1);
	       }
	       raise(SIGQUIT); }

       In general, the debugger dbx(1) is sufficient to deal with core images.

RELATED INFORMATION
       sigaction(2), uswitch(2), sysconfigdb(8), dbx(1) delim off

								       core(4)
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