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[linux] Linux looks at the log output of the Systemd service

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Posted on 11/15/2021 10:15:19 AM | | | |
systemd is the latest initialization system (init) of the Linux system, which is to improve the startup speed of the system, start as few processes as possible, and start as many processes as possible at the same time.

The process management command corresponding to systemd is systemctl

Check the service status through the systemctl command, and you can see the log output, the command is as follows:



The logs output by the service are written to/var/log/messageInside the file, you can view it with the journalctl command. journalctl can view all system log files, and due to the large amount of log information, journalctl also provides various parameters to help users locate log information more quickly.

journalctl common command

View all logs

By default, only the logs of this startup are saved

journalctl

View kernel logs (no application logs)

journalctl -k

.View the log of the system startup

journalctl   -b

journalctl  -b  -0

Review the log of the last launch

If you need to change the settings, such as the last system crash, you need to look at the last boot log when you need to view the logs.

journalctl  -b -1

View the log for the specified time

journalctl --since="2012-10-3018:17:16"

journalctl --since "20 minago"

journalctl --since yesterday

journalctl --since"2015-01-10" --until "2015-01-11 03:00"

journalctl --since 09:00 --until"1 hour ago"

journalctl --since"15:15" --until now

Displays the last 10 lines of the log at the tail

journalctl  -n

Displays a log with a specified number of rows at the end

I was looking at the logs in /var/log/messages, but the format was adjusted, such as the hostname format was different

journalctl -n 20

Real-time scrolling to display the latest logs

journalctl   -f

View logs for the specified service

journalctl  /usr/lib/systemd/systemd

View the logs for the specified process

journalctl   _PID=1

View the logs of scripts for a certain path

journalctl    /usr/bin/bash

View the logs of the specified user

journalctl _UID=33  --since today

Check the logs of a certain unit

journalctl  -u nginx.service

journalctl  -u nginx.service  --since  today

Real-time scrolling displays the latest log for a Unit

journalctl -u pmm-agent.service -f



Merge logs showing multiple units

journalctl  -u nginx.service  -u php-fpm.service  --since today





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