System information

kexec and kdump 211
2 Enable kdump init script:
chkconfig boot.kdump on
3 You can edit the options in /etc/sysconfig/kdump. Reading the comments
will help you understand the meaning of individual options.
4 Execute the init script once with rckdump start, or reboot the system.
After configuring kdump with the default values, check if it works as expected. Make
sure that no users are currently logged in and no important services are running on
your system. Then follow these steps:
1 Switch to runlevel 1 with telinit 1
2 Unmount all the disk file systems except the root file system with umount -a
3 Remount the root file system in read-only mode: mount -o remount,ro /
4 Invoke “kernel panic” with the procfs interface to Magic SysRq keys:
echo c >/proc/sysrq-trigger
IMPORTANT: The Size of Kernel Dumps
The KDUMP_KEEP_OLD_DUMPS option controls the number of preserved
kernel dumps (default is 5). Without compression, the size of the dump can
take up to the size of the physical RAM memory. Make sure you have suffi-
cient space on the /var partition.
The capture kernel boots and the crashed kernel memory snapshot is saved to the file
system. The save path is given by the KDUMP_SAVEDIR option and it defaults to /
var/crash. If KDUMP_IMMEDIATE_REBOOT is set to yes , the system automat-
ically reboots the production kernel. Log in and check that the dump has been created
under /var/crash.
WARNING: Screen Freezes in X11 Session
When kdump takes control and you are logged in an X11 session, the screen
will freeze without any notice. Some kdump activity can be still visible (for ex-
ample, deformed messages of a booting kernel on the screen).