man/man8/dumpadm.8

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 DUMPADM 8 "Aug 05, 2024"
 NAME
dumpadm - configure operating system crash dump
 SYNOPSIS
/usr/sbin/dumpadm [-Henpuy] [-c content-type] [-d dump-device]
 [-m mink | minm | min%] [-s savecore-dir]
 [-r root-dir] [-z on | off]


 DESCRIPTION
The dumpadm program is an administrative command that manages the
configuration of the operating system crash dump facility. A crash dump is a
disk copy of the physical memory of the computer at the time of a fatal system
error. When a fatal operating system error occurs, a message describing the
error is printed to the console. The operating system then generates a crash
dump by writing the contents of physical memory to a predetermined dump device,
which is typically a local disk partition. The dump device can be configured by
way of dumpadm. Once the crash dump has been written to the dump device,
the system will reboot.

Fatal operating system errors can be caused by bugs in the operating system,
its associated device drivers and loadable modules, or by faulty hardware.
Whatever the cause, the crash dump itself provides invaluable information to
your support engineer to aid in diagnosing the problem. As such, it is vital
that the crash dump be retrieved and given to your support provider. Following
an operating system crash, the savecore(8) utility is executed
automatically during boot to retrieve the crash dump from the dump device, and
write it to the file system. The directory in which the crash
dump is saved on reboot can also be configured using dumpadm.

When the operating system takes a crash dump the default behavior is to
compress the crash dump. This behavior is controlled by the -z option.
When compression is turned on, the savecore(8) utility writes one file
to the file system named vmdump.X. If compression is disabled, it instead
writes two files named unix.X and vmcore.X. In the uncompressed
case, both data files form the saved crash dump. In both cases X is an
integer identifying the dump.

For systems with a UFS root file system, the default dump device is configured
to be an appropriate swap partition. Swap partitions are disk partitions
reserved as virtual memory backing store for the operating system. Thus, no
permanent information resides in swap to be overwritten by the dump. See
swap(8). For systems with a ZFS root file system, dedicated ZFS volumes
are used for swap and dump areas. For further information about setting up a
dump area with ZFS, see the ZFS Administration Guide. To view the
current dump configuration, use the dumpadm command with no arguments:
example# dumpadm

 Dump content: kernel pages
 Dump device: /dev/dsk/c0t0d0s1 (swap)
Savecore directory: /var/crash/saturn
 Savecore enabled: yes
 Save compressed: on


When no options are specified, dumpadm prints the current crash dump
configuration. The example shows the set of default values: the dump content is
set to kernel memory pages only, the dump device is a swap disk partition, the
directory for savecore files is set to
/var/crash/hostname, savecore is set to run
automatically on reboot, and compression is turned on.

When one or more options are specified, dumpadm verifies that your
changes are valid, and if so, reconfigures the crash dump parameters and
displays the resulting configuration. You must be root to view or change
dump parameters.
 OPTIONS
The following options are supported:
-H

Do not print headers. This option is often paired with -p and only works
for the dump estimate size option, -e.


-c content-type

Modify the dump configuration so that the crash dump consists of the specified
dump content. The content should be one of the following:
kernel

Kernel memory pages only.


all

All memory pages.


curproc

Kernel memory pages, and the memory pages of the process whose thread was
currently executing on the CPU on which the crash dump was initiated. If the
thread executing on that CPU is a kernel thread not associated with any user
process, only kernel pages will be dumped.


-d dump-device

Modify the dump configuration to use the specified dump device. The dump device
may be one of the following:
dump-device

A specific dump device specified as an absolute pathname, such as
/dev/dsk/cNtNdNsN when the system is running a UFS root file
system. Or, specify a ZFS volume, such as /dev/zvol/dsk/rpool/dump, when
the system is running a ZFS root file system.


swap

If the special token swap is specified as the dump device, dumpadm
examines the active swap entries and selects the most appropriate entry to
configure as the dump device. See swap(8). Refer to the NOTES
below for details of the algorithm used to select an appropriate swap entry.
When the system is first installed with a UFS root file system, dumpadm
uses the value for swap to determine the initial dump device setting. A
given ZFS volume cannot be configured for both the swap area and the dump
device.


none

If the special token none is specified, the active dump device is removed
and crash dumps are disabled.


-e

Estimates the size of the dump for the current running system.


-m mink | minm | min%

Create a minfree file in the current savecore directory indicating that
savecore should maintain at least the specified amount of free space in
the file system where the savecore directory is located. The min argument
can be one of the following:
k

A positive integer suffixed with the unit k specifying kilobytes.


m

A positive integer suffixed with the unit m specifying megabytes.


%

A % symbol, indicating that the minfree value should be computed as the
specified percentage of the total current size of the file system containing
the savecore directory.


The savecore command will consult the minfree file, if present,
prior to writing the dump files. If the size of these files would decrease the
amount of free disk space below the minfree threshold, no dump files are
written and an error message is logged. The administrator should immediately
clean up the savecore directory to provide adequate free space, and re-execute
the savecore command manually. The administrator can also specify an
alternate directory on the savecore command-line.


-n

Modify the dump configuration to not run savecore automatically on
reboot. This is not the recommended system configuration; if the dump device is
a swap partition, the dump data will be overwritten as the system begins to
swap. If savecore is not executed shortly after boot, crash dump
retrieval may not be possible.


-p

Display numbers in parsable (exact) values and can only be used with -e.


-r root-dir

Specify an alternate root directory relative to which dumpadm should
create files. If no -r argument is specified, the default root directory
/ is used.


-s savecore-dir

Modify the dump configuration to use the specified directory to save files
written by savecore. The directory should be an absolute path and exist
on the system. If upon reboot the directory does not exist, it will be created
prior to the execution of savecore. See the NOTES section below for
a discussion of security issues relating to access to the savecore directory.
The default savecore directory is /var/crash/hostname where
hostname is the output of the -n option to the uname(1)
command.


-u

Forcibly update the kernel dump configuration based on the contents of
/etc/dumpadm.conf. Normally this option is used only on reboot when
starting svc:/system/dumpadm:default, when the dumpadm settings
from the previous boot must be restored. Your dump configuration is saved in
the configuration file for this purpose. If the configuration file is missing
or contains invalid values for any dump properties, the default values are
substituted. Following the update, the configuration file is resynchronized
with the kernel dump configuration.


-y

Modify the dump configuration to automatically run savecore on reboot.
This is the default for this dump setting.


-z on | off

Turns crash dump compression on or off.


 EXAMPLES
Example 1 Reconfiguring The Dump Device To A Dedicated Dump Device:

The following command reconfigures the dump device to a dedicated dump device:

example# dumpadm -d /dev/dsk/c0t2d0s2

 Dump content: kernel pages
 Dump device: /dev/dsk/c0t2d0s2 (dedicated)
 Savecore directory: /var/crash/saturn
 Savecore enabled: yes
 Save compressed: on

Example 2 Show estimated size of dump device:

The following commands will output the estimated dump device size,
usable for humans and in scripts.

example# dumpadm -e
Estimated dump size: 15.2G
example# dumpadm -ep
Estimated dump size: 16364603392
example# dumpadm -epH
16364605440

 EXIT STATUS
The following exit values are returned:
0

Dump configuration is valid and the specified modifications, if any, were made
successfully.


1

A fatal error occurred in either obtaining or modifying the dump configuration.


2

Invalid command line options were specified.


 FILES
/dev/dump

Dump device.


/etc/dumpadm.conf

Contains configuration parameters for dumpadm. Modifiable only through
that command.


savecore-directory/minfree

Contains minimum amount of free space for savecore-directory. See
savecore(8).


 SEE ALSO
 svcs (1),  uname (1),  attributes (7),  smf (7),  savecore (8),  svcadm (8),  swap (8)  NOTES
The system crash dump service is managed by the service management facility,
smf(7), under the service identifier:
svc:/system/dumpadm:default


Administrative actions on this service, such as enabling, disabling, or
requesting restart, can be performed using svcadm(8). The service's
status can be queried using the svcs(1) command.
 "Dump Device Selection"
When the special swap token is specified as the argument to dumpadm
-d the utility will attempt to configure the most appropriate swap device
as the dump device. dumpadm configures the largest swap block device as
the dump device; if no block devices are available for swap, the largest swap
entry is configured as the dump device. If no swap entries are present, or none
can be configured as the dump device, a warning message will be displayed.
While local and remote swap files can be configured as the dump device, this is
not recommended.
 "Dump Device/Swap Device Interaction (UFS File Systems Only)"
In the event that the dump device is also a swap device, and the swap device is
deleted by the administrator using the swap -d command, the
swap command will automatically invoke dumpadm -d swap
in order to attempt to configure another appropriate swap device as the dump
device. If no swap devices remain or none can be configured as the dump device,
the crash dump will be disabled and a warning message will be displayed.
Similarly, if the crash dump is disabled and the administrator adds a new swap
device using the swap -a command, dumpadm -d swap
will be invoked to re-enable the crash dump using the new swap device.

Once dumpadm -d swap has been issued, the new dump device is
stored in the configuration file for subsequent reboots. If a larger or more
appropriate swap device is added by the administrator, the dump device is not
changed; the administrator must re-execute dumpadm -d swap to
reselect the most appropriate device fom the new list of swap devices.
 "Minimum Free Space"
If the dumpadm -m option is used to create a minfree file
based on a percentage of the total size of the file system containing the
savecore directory, this value is not automatically recomputed if the file
system subsequently changes size. In this case, the administrator must
re-execute dumpadm -m to recompute the minfree value. If no
such file exists in the savecore directory, savecore will default to a
free space threshold of one megabyte. If no free space threshold is desired, a
minfree file containing size 0 can be created.
 "Security Issues"
If, upon reboot, the specified savecore directory is not present, it will be
created prior to the execution of savecore with permissions 0700 (read,
write, execute by owner only) and owner root. It is recommended that
alternate savecore directories also be created with similar permissions, as the
operating system crash dump files themselves may contain secure information.