NetBSD/share/man/man5/core.5

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.\"     @(#)core.5	8.3 (Berkeley) 12/11/93
.\"
.Dd December 11, 1993
.Dt CORE 5
.Os
.Sh NAME
.Nm core
.Nd memory image file format
.Sh SYNOPSIS
.Fd #include <sys/param.h>
.Sh DESCRIPTION
A small number of signals which cause abnormal termination of a process
also cause a record of the process's in-core state to be written
to disk for later examination by one of the available debuggers
(see
.Xr signal 7 ).
This memory image is written to a file named from a per-process template;
provided the terminated process had write permission, and provided the
abnormality did not cause a system crash.
(In this event, the decision to save the core file is arbitrary, see
.Xr savecore 8 . )
The file is named from a per-process template, mapped to the sysctl
variable
.Em proc.<pid>.corename
(where <pid> has to be replaced by the pid in decimal format of the
process).
This template is either an absolute or relative path name, in which format
characters can be used, preceeded by the percent character (``%''). 
The following characters are recognised as format and subsitued:
.Bl -column "cAA" "The process's creation date (in seconds)xxx" -offset indent
.It Li n        The process's name
.It Li p        The PID of the process (in decimal) 
.It Li t        The process's creation date (a la
.Xr time 3 ,
in decimal)
.It Li u        The login name, as returned by
.Xr getlogin 2
.El
.Pp
By default, the per-process template string points to the default core name
template, which is mapped to the sysctl variable
.Em kern.defcorename .
Changing this value on a live system will change the core name template for
all processes which didn't have a per-process template set.
The default value of the default core name template is
.Nm %n.core
and can be changed at compile-time with the kernel configuration option
.Cd options DEFCORENAME
(see
.Xr options 4 )
.Pp
The per-process template string is inherited on process creation, but is reset
to point to the default core name template on execution of a set-id binary.
.Pp
The maximum size of a core file is limited by
.Xr setrlimit 2 .
Files which would be larger than the limit are not created.
.Pp
The core file consists of the
.Fa u. area ,
whose size (in pages) is defined by the
.Dv UPAGES
manifest in the
.Aq Pa sys/param.h
file.  The 
.Fa u. area
starts with a 
.Fa user
structure as given in
.Aq Pa sys/user.h .
The remainder of the core file consists of the data pages followed by
the stack pages of the process image.
The amount of data space image in the core file is given (in pages) by the
variable
.Fa u_dsize
in the
.Fa u. area .
The amount of stack image in the core file is given (in pages) by the
variable 
.Fa u_ssize
in the 
.Fa u. area .
The size of a ``page'' is given by the constant
.Dv NBPG
(also from
.Aq Pa sys/param.h ) .
.Sh SEE ALSO
.Xr gdb 1 ,
.Xr setrlimit 2 ,
.Xr sysctl 3 ,
.Xr signal 7 ,
.Xr sysctl 8
.Sh HISTORY
A
.Nm core
file format appeared in
.At v6 .