System Administration Guide: Advanced Administration

System Crashes (Overview)

System crashes can occur due to hardware malfunctions, I/O problems, and software errors. If the system crashes, it will display an error message on the console, and then write a copy of its physical memory to the dump device. The system will then reboot automatically. When the system reboots, the savecore command is executed to retrieve the data from the dump device and write the saved crash dump to your savecore directory. The saved crash dump files provide invaluable information to your support provider to aid in diagnosing the problem.

System Crash Dump Files

The savecore command runs automatically after a system crash to retrieve the crash dump information from the dump device and writes a pair of files called unix.X and vmcore.X, where X identifies the dump sequence number. Together, these files represent the saved system crash dump information.

Crash dump files are sometimes confused with core files, which are images of user applications that are written when the application terminates abnormally.

Crash dump files are saved in a predetermined directory, which by default, is /var/crash/hostname. In previous Solaris releases, crash dump files were overwritten when a system rebooted—unless you manually enabled the system to save the images of physical memory in a crash dump file. Now the saving of crash dump files is enabled by default.

System crash information is managed with the dumpadm command. For more information, see The dumpadm Command.

Saving Crash Dumps

You can examine the control structures, active tables, memory images of a live or crashed system kernel, and other information about the operation of the kernel by using the mdb utility. Using mdb to its full potential requires a detailed knowledge of the kernel, and is beyond the scope of this manual. For information on using this utility, see mdb(1M).

Additionally, crash dumps saved by savecore can be useful to send to a customer service representative for analysis of why the system is crashing.

The dumpadm Command

Use the dumpadm command to manage system crash dump information in the Solaris environment.

The following table describes dumpadm's configuration parameters.

Dump Parameter 

Description 

dump device 

The device that stores dump data temporarily as the system crashes. When the dump device is not the swap area, savecore runs in the background, which speeds up the boot process.

savecore directory 

The directory that stores system crash dump files. 

dump content 

Type of data, kernel memory or all of memory, to dump.  

minimum free space 

Minimum amount of free space required in the savecore directory after saving crash dump files. If no minimum free space has been configured, the default is one Mbyte.

For more information, see dumpadm(1M).

The dump configuration parameters managed by the dumpadm command are stored in the /etc/dumpadm.conf file.


Note –

Do not /etc/dumpadm.conf edit manually. This could result in an inconsistent system dump configuration.


How the dumpadm Command Works

During system startup, the dumpadm command is invoked by the /etc/init.d/savecore script to configure crash dumps parameters based on information in the /etc/dumpadm.conf file.

Specifically, it initializes the dump device and the dump content through the /dev/dump interface.

After the dump configuration is complete, the savecore script looks for the location of the crash dump file directory by parsing the content of /etc/dumpadm.conf file. Then, savecore is invoked to check for crash dumps. It will also check the content of the minfree file in the crash dump directory.

Dump Devices and Volume Managers

Do not configure a dedicated dump device that is under the control of volume management product such as Solaris Volume Manager for accessibility and performance reasons. You can keep your swap areas under the control of Solaris Volume Manager and this is a recommend practice, but keep your dump device separate.