How to use the journalctl command under Linux
This article mainly shows you "how to use journalctl commands under Linux". The content is simple and clear. I hope it can help you solve your doubts. Let me lead you to study and learn this article "how to use journalctl commands under Linux".
Log management tool journalctl is a proprietary log management tool on centos7, which reads information from the file message. Systemd uniformly manages startup logs for all Unit.
Use method $man journalctl
$journalctl-help
Common methods
$journalctl
When there is no option, all log records are output by default
$journalctl-n [num]
Displays the log of the last num line. If num is omitted, the last 10 lines are displayed by default
$journalctl-f
Scrolling the latest log in real time
$journalctl-u
Displays the logs of the specified unit. Unit_name is a specific unit name. If you want to merge and display multiple unit logs, you can use multiple-u
$journalctl-o
Set the format of log output. The value of mode is (short, short-iso,short-precise, short-monotonic, verbose,export, json, json-pretty, json-sse, ca).
$journalctl-no-pager
Log default paging output,-no-pager changed to normal standard output
$journalctl-since
Display data from a certain point in time
Journalctl-since= "2020-08-31 10:00:00" # shows data after 10:00 on 31 August 2020
Journalctl-since "10 min ago" # displays logs for the last 10 minutes
Journalctl-since today/yesterday # shows logs since today / yesterday
Journalctl-since "2020-08-31 10:00:00"-until "2020-08-31 11:00:00" # shows logs for a certain period of time (2020-08-31 10:00-11:00)
# until can also be used as follows:
-until "1 hour ago"
-until now
$journalctl-k
View the system kernel log
Match
$journalctl-o json-n 1
You can see the json output format of the latest log. We can match the corresponding log according to the key and value of json.
$journalctl _ PID=28655
Gets the log of the specified process
$journalctl _ UID=33-since=today
View the log of the specified user today
$journalctl _ SYSTEMD_UNIT=cron.service PRIORITY=6
Matching through system unit and priority
View logs with a specified priority (and above)
There are 8 levels of log priority.
0: emerg
1: alert
2: crit
3: err
4: warning
5: notice
6: info
7: debug
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