Journalctl

Journalctl command allows to query the contents of the systemd journal/logs.

Configuration

• /etc/systemd/journald.conf

Basic Commands

• journalctl or journalctl --no-pager
• journalctl -r (reverse order)
• journalctl -k : Show only kernel messages
• journalctl -f (follow)
• journalctl -u service-name.service

journalctl -u libvirtd

• journalctl --verify
• Disk Usage/Logging: /journalctl --disk-usage/
• journalctl --vacuum-size=200M
  • --vacuum-size=BYTES Reduce disk usage below specified size
  • --vacuum-files=INT Leave only the specified number of journal files
  • --vacuum-time=TIME Remove journal files older than specified time
• journalctl --list-boots. See also: last (command)
• journalctl -xb

-x --catalog Includes explanations in log lines from message catalgog

-b show message from current boot. if [ID] is provided will show messages from that specific boot.

See also

• systemd and related daemons: systemd, systemd-journald, systemd-logind, systemd-networkd (networkctl), systemd-timesyncd, systemd-resolved and systemd-udevd
• /etc/inittab and respawn option
• systemctl
• launchd init and operating system service management daemon for MacOS

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Source: https://en.wikiversity.org/wiki/Linux_Administration/System_Services/System_Logging/Journalctl