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howto: Notes on watchdog module handling

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Update howto with notes on dracut and kernel watchdog module handling.

Signed-off-by: Pratyush Anand <panand@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>
This commit is contained in:
Pratyush Anand 2016-07-20 23:42:22 +05:30 committed by Dave Young
parent 6a2b39b96e
commit effd035e34
1 changed files with 14 additions and 0 deletions
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kexec-kdump-howto.txt
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@ -616,6 +616,20 @@ options are copied from /proc/cmdline. In general it is best to append
command line options using "KDUMP_COMMANDLINE_APPEND=" instead of replacing
the original command line completely.
Notes on watchdog module handling:
If a watchdog is active in first kernel then, we must have it's module
loaded in crash kernel, so that either watchdog is deactivated or started
being kicked in second kernel. Otherwise, we might face watchdog reboot
when vmcore is being saved. When dracut watchdog module is enabled, it
installs kernel watchdog module of active watchdog device in initrd.
kexec-tools always add "-a watchdog" to the dracut_args if there exists at
least one active watchdog and user has not added specifically "-o watchdog"
in dracut_args of kdump.conf. If a watchdog module (such as hp_wdt) has
not been written in watchdog-core framework then this option will not have
any effect and module will not be added. Please note that only systemd
watchdog daemon is supported as watchdog kick application.
Parallel Dumping Operation
==========================
Kexec allows kdump using multiple cpus. So parallel feature can accelerate