NetBSD/sbin/savecore/savecore.8

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.\"     @(#)savecore.8	8.1 (Berkeley) 6/5/93
.\"
.Dd September 13, 2011
.Dt SAVECORE 8
.Os
.Sh NAME
.Nm savecore
.Nd save a core dump of the operating system
.Sh SYNOPSIS
.Nm
.Op Fl fvz
.Op Fl N Ar system
.Op Fl Z Ar level
.Op Ar directory
.Nm
.Fl c
.Op Fl v
.Op Fl N Ar system
.Nm
.Fl n
.Op Fl v
.Op Fl N Ar system
.Sh DESCRIPTION
When the
.Nx
kernel encounters a fatal error, the
.Xr panic 9
routine arranges for a snapshot of the contents of physical memory to
be written into a dump area, typically in the swap partition.
.Pp
Upon a subsequent reboot,
.Nm
is typically run out of
.Xr rc 8 ,
before swapping is enabled, to copy the kernel and the saved memory image
into
.Fa directory ,
and enters a reboot message and information about the core dump into
the system log.
If a directory is not specified, then
.Pa /var/crash
is used.
.Pp
The kernel and core file can then be analyzed using various tools,
including
.Xr crash 8 ,
.Xr dmesg 8 ,
.Xr fstat 1 ,
.Xr gdb 1 ,
.Xr iostat 8 ,
.Xr netstat 1 ,
.Xr ps 1 ,
and
.Xr pstat 8 ,
to attempt to deduce the cause of the crash.
.Pp
Crashes are usually the result of hardware faults or kernel bugs.
If a kernel bug is suspected, a full bug report should be filed at
.Lk http://www.netbsd.org/ ,
or using
.Xr send-pr 1 ,
containing as much information as possible about the circumstances of
the crash.
Since crash dumps are typically very large and may contain
whatever (potentially confidential) information was in memory at the
time of the crash, do
.Em NOT
include a copy of the crash dump file in the bug report; instead, save it
somewhere in the event that a
.Nx
developer wants to examine it.
.Pp
The options are as follows:
.Bl -tag -width directory
.It Fl c
Only clears the dump without saving it, so that future invocations of
.Nm
will ignore it.
.It Fl f
Forces a dump to be taken even if the dump doesn't appear correct or there
is insufficient disk space.
.It Fl n
Check whether a dump is present without taking further action.
The command exits with zero status if a dump is present, or with non-zero
status otherwise.
.It Fl N
Use
.Ar system
as the kernel instead of the default (returned by
.Xr getbootfile 3 ) .
Note that
.Xr getbootfile 3
uses
.Xr secure_path 3
to check that kernel file is
.Dq secure
and will default to
.Pa /netbsd
if the check fails.
.It Fl v
Prints out some additional debugging information.
.It Fl z
Compresses the core dump and kernel (see
.Xr gzip 1 ) .
.It Fl Z Ar level
Set the compression level for
.Fl z
to
.Ar level .
Defaults to 1 (the fastest compression mode).
Refer to
.Xr gzip 1
for more information regarding the compression level.
.El
.Pp
.Nm
checks the core dump in various ways to make sure that it is current and
that it corresponds to the currently running system.
If it passes these checks, it saves the core image in
.Ar directory Ns Pa /netbsd.#.core
and the system in
.Ar directory Ns Pa /netbsd.#
(or in
.Ar directory Ns Pa /netbsd.#.core.gz
and
.Ar directory Ns Pa /netbsd.#.gz ,
respectively, if the
.Fl z
option is used).
The
.Dq #
is the number from the first line of the file
.Ar directory Ns Pa /bounds ,
and it is incremented and stored back into the file each time
.Nm
successfully runs.
.Pp
.Nm
also checks the available disk space before attempting to make the copies.
If there is insufficient disk space in the file system containing
.Ar directory ,
or if the file
.Ar directory Ns Pa /minfree
exists and the number of free kilobytes (for non-superusers) in the
file system after the copies were made would be less than the number
in the first line of this file, the copies are not attempted.
.Pp
If
.Nm
successfully copies the kernel and the core dump, the core dump is cleared
so that future invocations of
.Nm
will ignore it.
.Sh SEE ALSO
.Xr fstat 1 ,
.Xr gdb 1 ,
.Xr gzip 1 ,
.Xr netstat 1 ,
.Xr ps 1 ,
.Xr send-pr 1 ,
.Xr crash 8 ,
.Xr dmesg 8 ,
.Xr iostat 8 ,
.Xr pstat 8 ,
.Xr rc 8 ,
.Xr syslogd 8 ,
.Xr panic 9
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.1 .
.Sh BUGS
The minfree code does not consider the effect of compression.