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core(4)								      core(4)



NAME
  core - Format	of memory image	file

SYNOPSIS

  #include <&lt;sys/core.h>&gt;

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, overwriting
  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

  core
      The literal string core.

  program_name
      Up to sixteen characters taken from the program name as shown by the ps
      command.

  host_name
      The first	portion	of the system's	network	host name, or up to 16 char-
      acters of	the host name, taken from the part of the host name that pre-
      cedes the	first dot.

  numeric_tag
      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 sec-
    tion.

  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 system confi-
  guration 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 maximum is 99,999, and the default is 16.


EXAMPLE

  The following	example	shows a	code fragment that calls the uswitch system
  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)