freebsd-dev/sbin/savecore/savecore.8
Mark Johnston 64a16434d8 Add support for compressed kernel dumps.
When using a kernel built with the GZIO config option, dumpon -z can be
used to configure gzip compression using the in-kernel copy of zlib.
This is useful on systems with large amounts of RAM, which require a
correspondingly large dump device. Recovery of compressed dumps is also
faster since fewer bytes need to be copied from the dump device.

Because we have no way of knowing the final size of a compressed dump
until it is written, the kernel will always attempt to dump when
compression is configured, regardless of the dump device size. If the
dump is aborted because we run out of space, an error is reported on
the console.

savecore(8) is modified to handle compressed dumps and save them to
vmcore.<index>.gz, as it does when given the -z option.

A new rc.conf variable, dumpon_flags, is added. Its value is added to
the boot-time dumpon(8) invocation that occurs when a dump device is
configured in rc.conf.

Reviewed by:	cem (earlier version)
Discussed with:	def, rgrimes
Relnotes:	yes
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D11723
2017-10-25 00:51:00 +00:00

190 lines
5.1 KiB
Groff

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.\" From: @(#)savecore.8 8.1 (Berkeley) 6/5/93
.\" $FreeBSD$
.\"
.Dd October 24, 2017
.Dt SAVECORE 8
.Os
.Sh NAME
.Nm savecore
.Nd "save a core dump of the operating system"
.Sh SYNOPSIS
.Nm
.Fl c
.Op Fl v
.Op Ar device ...
.Nm
.Fl C
.Op Fl v
.Op Ar device ...
.Nm
.Op Fl -libxo
.Op Fl fkvz
.Op Fl m Ar maxdumps
.Op Ar directory Op Ar device ...
.Sh DESCRIPTION
The
.Nm
utility
copies a core dump into
.Ar directory ,
or the current working directory if no
.Ar directory
argument is given,
and enters a reboot message and information about the core dump into
the system log.
.Pp
The options are as follows:
.Bl -tag -width ".Fl m Ar maxdumps"
.It Fl -libxo
Generate output via
.Xr libxo 3
in a selection of different human and machine readable formats.
See
.Xr xo_parse_args 3
for details on command line arguments.
.It Fl C
Check to see if a dump exists,
and display a brief message to indicate the status.
An exit status of 0 indicates that a dump is there,
1 indicates that none exists.
This option is compatible only with the
.Op Fl v
option.
.It Fl c
Clear the dump, so that future invocations of
.Nm
will ignore it.
.It Fl f
Force a dump to be taken even if either the dump was cleared or if the
dump header information is inconsistent.
.It Fl k
Do not clear the dump after saving it.
.It Fl m Ar maxdumps
Maximum number of dumps to store.
Once the number of stored dumps is equal to
.Ar maxdumps
the counter will restart from
.Dv 0 .
.It Fl v
Print out some additional debugging information.
Specify twice for more information.
.It Fl z
Compress the dump (see
.Xr gzip 1 ) .
The dump may already be compressed if the kernel was configured to
do so by
.Xr dumpon 8 .
In this case, the option has no effect.
.El
.Pp
The
.Nm
utility
looks for dumps on each device specified by the
.Ar device
argument(s), or on each device in
.Pa /etc/fstab
marked as
.Dq dump
or
.Dq swap .
The
.Nm
utility
checks the core dump in various ways to make sure that it is complete.
If it passes these checks, it saves the core image in
.Ar directory Ns Pa /vmcore.#
and information about the core in
.Ar directory Ns Pa /info.# .
If the core is encrypted, it saves the dump key in
.Ar directory Ns Pa /key.# .
The core can be later decrypted using
.Xr decryptcore 8 .
For kernel textdumps generated with the
.Xr textdump 4
facility, output will be stored in the
.Xr tar 5
format and named
.Ar directory Ns Pa /textdump.tar.# .
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
The
.Nm
utility
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.
.Pp
The
.Nm
utility
is meant to be called near the end of the initialization file
.Pa /etc/rc
(see
.Xr rc 8 ) .
.Sh SEE ALSO
.Xr gzip 1 ,
.Xr getbootfile 3 ,
.Xr libxo 3 ,
.Xr xo_parse_args 3 ,
.Xr textdump 4 ,
.Xr tar 5 ,
.Xr decryptcore 8 ,
.Xr dumpon 8 ,
.Xr syslogd 8
.Sh HISTORY
The
.Nm
utility appeared in
.Bx 4.1 .
.Pp
Support for kernel textdumps appeared in
.Fx 7.1 .
.Sh BUGS
The minfree code does not consider the effect of compression or sparse files.