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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

The above is all the contents of this article entitled "how to use journalctl commands under Linux". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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