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Doc: add a documentation for the usage of logger

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Because the logger is introduced to output the kdump logs, need to
add a documentation for this change and describe how to use it.

Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
Acked-by: Kairui Song <kasong@redhat.com>
This commit is contained in:
Lianbo Jiang 2020-10-27 17:04:26 +08:00 committed by Kairui Song
parent d7054f4cd8
commit d4c6f56456
1 changed files with 35 additions and 0 deletions
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35
kexec-kdump-howto.txt
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@ -885,3 +885,38 @@ Debugging Tips
minicom -C /tmp/console-logs
Now minicom should be logging serial console in file console-logs.
- Using the logger to output kdump log messages
Currently, kdump messages are printed with the 'echo' command or redirect
to console, and which does not support to output kdump messages according
to the log level.
That is not convenient to debug kdump issues, we usually need to capture
additional debugging information via the modification of the options or the
scripts like kdumpctl, mkdumprd, etc. Because there is no complete debugging
messages, which could waste valuable time.
To cope with this challenging, we introduce the logger to output the kdump
messages according to the log level, and provide a chance to save logs to
the journald if the journald service is available, and then dump all logs
to a file, otherwise dump the logs with the dmesg to a file.
Logging is controlled by following global variables:
- @var kdump_stdloglvl - logging level to standard error (console output)
- @var kdump_sysloglvl - logging level to syslog (by logger command)
- @var kdump_kmsgloglvl - logging level to /dev/kmsg (only for boot-time)
If any of the variables is not set, this function set it to default:
- @var kdump_stdloglvl=4 (info)
- @var kdump_sysloglvl=4 (info)
- @var kdump_kmsgloglvl=0 (no logging)
Logging levels: fatal(1),error(2),warn(3),info(4),debug(5),trace(6)
We can easily configure the above variables in the /etc/sysconfig/kdump. For
example:
kdump_sysloglvl=5
kdump_stdloglvl=5
The above configurations indicate that kdump messages will be printed to the
console and journald if the journald service is enabled.