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man pages section 8: System Administration Commands

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Updated: Thursday, June 13, 2019
 
 

dumpadm(8)

Name

dumpadm - configure operating system crash dump

Synopsis

/usr/sbin/dumpadm [-enpuy] [
-c content-spec] [-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 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 preserving the contents of physical memory in RAM. If this is not possible, the contents of physical memory are written to a predetermined dump device, which can be a ZFS ZVOL, or a local disk partition.

Once the crash dump has been preserved, 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 and write it to your file system in compressed form, to files named vmdump.X, and vmdump-<secname>.X, where X is an integer identifying the dump. Afterwards, savecore(8) can be invoked on the same or another system to expand the compressed crash dump to files named vmcore.X and vmcore-<secname>.X. The directory in which the crash dump is saved on reboot can be configured using dumpadm command.

By default dedicated ZFS volumes are used for dump devices. 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 with ZFS metadata
       Dump device: /dev/zvol/dsk/rpool/dump (dedicated)
Savecore directory: /var/crash
  Savecore enabled: yes
   Save compressed: on

When no options are specified, dumpadm displays the current crash dump configuration. The example above shows the set of default values: the dump content is set to kernel memory pages and ZFS meta data only. The crash dump will be preserved in memory (if possible), else a dump device will be used. The dump device is by default a zvol in the root pool. The directory for savecore files is set to /var/crash/. savecore is configured to run automatically on reboot and save the crash dump in a compressed format.

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.

Upon system installation, dumpadm establishes a dump device of sufficient size, based on system memory size and other internal information, to accommodate a dump file. If you subsequently attempt to create a dump device that is too small to store the dump file, dumpadm issues a warning message.

Options

The following options are supported:

–c content-spec

Modify the dump configuration so that the crash dump consists of the specified dump content. The content-spec comprises of optional content-type and content modifiers:

[ content-type ] [ +content-modifier | -content-modifier.. ]

content-type provides the basis, the content modifiers further change the contents to be dumped. With +, the content modifiers add extra data to be dumped, with - the data is left out.

The content-type can be one of the following:

kernel

Kernel memory pages only. Note that this includes only basic set of kernel pages, that is, not the pages which can be specified with content modifiers.

all

All memory pages. If all is specified, the system image is written to the dump device. Note that the resulting dump will include pages for filesystem buffers.

curproc

Kernel memory pages (as specified by 'kernel'), 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.

allproc

Kernel memory pages (as specified by 'kernel') and all process pages. If allproc is specified, the system image is written to the dump device.

The content-modifier can be one of the following:

zfs

Kernel pages which store ZFS metadata.

The content modifiers affect which portions of kernel memory are dumped and which are not. They do not have any effect when the 'all' content type is set.

If content-type is omitted, and only a content-modifier is specified, then the currently configured content-type will remain unchanged.

–d dump-device

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

dump-device

A block device specified as an absolute pathname, such as/dev/dsk/cNtNdNsN, or a ZFS volume such as /dev/zvol/dsk/rpool/dump.

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.

A given ZFS volume cannot be configured for both the swap area and the dump device.

Use of a swap device for a dump device is not recommended.

none

Do not use disk based dump device. The crash dump will still be retrieved if it is possible to store crash dumps in memory.

–e

Print estimate of disk space required for storing compressed crash dump. The value is computed using current configuration and currently 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. The system will attempt to preserve a crash dump image in memory. If dumpadm –n is set, then the crash dump image is written to the dump device after the system is rebooted. savecore (8) can then be run manually once the system has booted up to extract the crash dump to the savecore directory.

If the dump device is a swap partition, the dump data may be overwritten as the system begins to use the swap device. If savecore is not executed shortly after boot, crash dump retrieval may not be possible.

–p

Produce machine parseable output.

–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/dump:config, 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. See NOTES.

–z on | off

Modify the dump configuration to control the operation of savecore on reboot. The options are on, to enable saving core files in a compressed format, and off, to automatically uncompress the crash dump file. The default is on, because crash dump files can be very large and require less file system space if saved in a compressed format.

Examples

Example 1 Reconfiguring The Dump Device to store current process pages and no ZFS meta data pages

example# dumpadm -c curproc-zfs
                   Dump content: kernel and current process without ZFS metadata
                    Dump device: /dev/zvol/dsk/rpool/dump (dedicated)
             Savecore directory: /var/crash
               Savecore enabled: yes
                Save compressed: on

Example 2 Specifying allproc or all content

example# dumpadm -c all
                   Dump content: all
                    Dump device: /dev/zvol/dsk/rpool/dump (dedicated)
             Savecore directory: /var/crash
               Savecore enabled: yes
                Save compressed: on
Example 3 Preserving crash dump if savecore is disabled

If savecore is disabled, the crash dump may still be preserved in memory and copied to the dump device after reboot. It can be extracted later by running savecore (8) manually


example# dumpadm -n -c kernel+zfs
                   Dump content: kernel with ZFS metadata
                    Dump device: /dev/zvol/dsk/rpool/dump (dedicated)
             Savecore directory: /var/crash
               Savecore enabled: yes
                Save compressed: on

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

Crash dump management device driver.

/etc/dumpadm.conf

Contains configuration parameters for dumpadm and savecore. Modifiable only using dumpadm.

savecore-directory/minfree

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

Attributes

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Availability
system/core-os

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 following service identifiers:

svc:/system/dump:config
svc:/system/dump:deferred
svc:/system/dump:disk
svc:/system/dump:swap

While administrative actions on this service, such as enabling, disabling, or requesting restart, can be performed using svcadm(8), it is not recommended to disable these services. The status of these services 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.

Dump Device/Swap Device Interaction

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 from 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.

If there is insufficient space in the dump directory, and system preserved a crash dump image in memory, then the image is written to the dump device for later extraction using savecore (8) .

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.

Default for savecore

System installation software might reserve a dedicated dump device (for example, a disk slice or a ZFS volume). In such a case, the dumpadm default can be set to –n, meaning that savecore does not run automatically when the system reboots. A crash image will be preserved on the dump device even if initially it was preserved in memory. Run /usr/bin/savecore manually as root to retrieve the crash image and copy it to set of files under /var/crash. The crash image will remain on the dump device until overwritten by a later one.