System information

218 System Analysis and Tuning Guide
You can change the directory for the kernel dumps with the KDUMP_SAVEDIR
option. Keep in mind that the size of kernel dumps can be very large. kdump will
refuse to save the dump if the free disk space, subtracted by the estimated dump
size, drops below the value specified by the KDUMP_FREE_DISK_SIZE option.
Note that KDUMP_SAVEDIR understands URL format protocol://spec-
ification, where protocol is one of file, ftp, sftp, nfs or cifs,
and specification varies for each protocol. For example, to save ker-
nel dump on an FTP server, use the following URL as a template: ftp://
username:[e-mail]:123/var/crash.
Kernel dumps are usually huge and contain many pages that are not necessary for
analysis. With KDUMP_DUMPLEVEL option, you can omit such pages. The option
understands numeric value between 0 and 31. If you specify 0, the dump size will be
largest. If you specify 31, it will produce the smallest dump. For a complete table of
possible values, see the manual page of kdump (man 7 kdump).
Sometimes it is very useful to make the size of the kernel dump smaller. For exam-
ple, if you want to transfer the dump over the network, or if you need to save some
disk space in the dump directory. This can be done with KDUMP_DUMPFORMAT set
to compressed. The crash utility supports dynamic decompression of the com-
pressed dumps.
IMPORTANT: Changes to kdump Configuration File
You always need to execute rckdump restart after you make manual
changes to /etc/sysconfig/kdump. Otherwise these changes will take
effect next time you reboot the system.
18.9 For More Information
Since there is no single comprehensive reference to kexec and kdump usage, you have
to explore several resources to get the information you need. Here are some of them:
• For the kexec utility usage, see the manual page of kexec (man 8 kexec).
• You can find general information about kexec at http://www.ibm.com/de
veloperworks/linux/library/l-kexec.html . Might be slightly out-
dated.