Using the Kernel Dump Configuration Utility

Enabling the Service

To start the kdump daemon at boot time, select the Enable kdump check box. This will enable the service for runlevels 2, 3, 4, and 5, and start it for the current session. Similarly, unselecting the check box will disable it for all runlevels and stop the service immediately.

Configuring the Memory Usage

To configure the amount of memory that is reserved for the kdump kernel, click the up and down arrow buttons next to the New kdump Memory field to increase or decrease the value. Notice that the Usable Memory field changes accordingly showing you the remaining memory that will be available to the system.

Configuring the Target Type

When a kernel crash is captured, the core dump can be either stored as a file in a local file system, written directly to a device, or sent over a network using the NFS (Network File System) or SSH (Secure Shell) protocol. To change this, click the Edit Location button, and select a location type as described below.

Figure 44.3. The Edit Location dialog

To save the dump to the local file system, select file from the pulldown list. Optionally, if you wish to write the file to a different partition, select ext3 or ext2 from the pulldown list according to the file system you are using, and enter a valid device name to the Enter location field. Note that after clicking OK, you can then customize the destination directory by changing the value in the Path field at the bottom.

To write the dump directly to a device, select raw from the pulldown list, and enter a valid device name (for example, /dev/sdb1). When you are done, click OK to confirm your choice.

To store the dump to a remote machine using the NFS protocol, select nfs from the pulldown list, and enter a valid target in the hostname:directory form (for example, penguin.example.com:/export). Clicking the OK button will confirm your changes. Finally, edit the value of the Path field to customize the destination directory (for instance, cores).

To store the dump to a remote machine using the SSH protocol, select ssh from the pulldown list, and enter a valid username and hostname in the username@hostname form (for example, john@penguin.example.com). Clicking the OK button will confirm your changes. Finally, edit the value of the Path field to customize the destination directory (for instance, /export/cores).

Refer to OpenSSH for information on how to configure an SSH server, and how to set up a key-based authentication.

Configuring the Core Collector

To reduce the size of the vmcore dump file, kdump allows you to specify an external application (that is, a core collector) to compress the data, and optionally leave out all irrelevant information. Currently, the only fully supported core collector is makedumpfile.

To enable the dump file compression, make sure the -c parameter is listed after the makedumpfile command in the Core Collector field (for example, makedumpfile -c).

To remove certain pages from the dump, add the -d value parameter after the makedumpfile command in the Core Collector field. The value is a sum of values of pages you want to omit as described in Table 44.1, "Supported filtering levels". For example, to remove both zero and free pages, use makedumpfile -d 17.

Refer to the manual page for makedumpfile for a complete list of available options.

Changing the Default Action

To choose what action to perform when kdump fails to create a core dump, select the appropriate option from the Default Action pulldown list. Available options are mount rootfs and run /sbin/init (the default action), reboot (to reboot the system), shell (to present a user with an interactive shell prompt), and halt (to halt the system).