Re: core_pattern pipe documentation

[Neil Horman <nhorman-2XuSBdqkA4R54TAoqtyWWQ@public.gmane.org>]

On Wed, Apr 23, 2008 at 02:09:14PM +0200, Michael Kerrisk wrote:
> Andi -- ping!
> 
> Adding Neil to CC, since it looks like he also did some work here, and
> so can perhaps comment.
> 
> On Fri, Apr 18, 2008 at 6:53 PM, Michael Kerrisk
> <mtk.manpages-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org> wrote:
> > Andi,
> >
> > I wrote the following description of the core_pattern pipe feature.  Does this
> > seem okay?
> >
> >   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 interpreted 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  path-
> >          name  (or  a  pathname relative to the root directory,
> >          /), and must immediately follow the '|' character.
> >
> >       *  The process created to run the program  runs  as  user
> >          and group root.
> >
> >       *  Arguments can be supplied to the program, delimited by
> >          white space (up to a total line length of 128  bytes).
> >
> > Cheers,
> >
> > Michael
> >
Thanks for CC'ing me.  The above all looks good.  I would add documentation
however, about the available macros that can be used when core_pattern is
specified as a pipe.  Adding something like the following would be good:

	* Arguments can be statically declared or implied via the use of macros,
	  denoted by the use of the %sign.  The following macros are supported:
		* %% - output a literal % sign on the command line
		* %p - the pid of the crashing process
		* %u - the uid of the crashing process
		* %g - the gid of the crashing process
		* %s - the signal that caused the crashing process to crash
		* %t - the time the crashing process dumped
		* %h - the hostname of the system
		* %e - the executable name of the crashing process
		* %c - the core limit size of the crashing process

	  Note that the core limit size macro may be a different value than what
	  is returned by getrlimit(RLIMIT_CORE,...).  This is due to the fact
	  that the core_pattern specified executible will be run as the same uid
	  as the crashing process, and to facilitate reception of the entire
	  core, the kernel will temporarily set RLIMIT_CORE to unlimited while
	  the dump is in progress.  Note also %u and %g may be different values
	  than getuid/getgid in the event that the core_pattern executable is
	  set[u|g]id root


Thanks & Regards
Neil


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