DUMPADM(1M) Maintenance Commands DUMPADM(1M)

dumpadm - configure operating system crash dump 

/usr/sbin/dumpadm [-enuy] [-c content-type] [-d dump-device]
     [ -m mink | minm | min%] [-s savecore-dir]
     [ -r root-dir] [-z on | off]

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(1M) 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(1M) 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(1M). 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
  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, 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.

The following options are supported:
-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(1M). 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.
-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.
-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.

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
       Savecore enabled: yes
        Save compressed: on

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.

/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(1M).

svcs(1), uname(1), savecore(1M), svcadm(1M), swap(1M), attributes(5), smf(5)

The system crash dump service is managed by the service management facility, smf(5), 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(1M). The service's status can be queried using the svcs(1) command.

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.

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.

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.

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.
February 13, 2017