journalctl
queries and displays messages from the systemd journal
TLDR
Show all messages with priority level 3 (errors) from this boot
$ journalctl -b -p 3
Follow new messages (like tail -f)$ journalctl -n 50 -f
Show all messages by a specific unit$ journalctl -u [unit]
Filter messages within a time range$ journalctl --since yesterday --until today
Show all messages by a specific process$ journalctl _PID=[pid]
Grep for a pattern in log messages$ journalctl -g "[pattern]"
Delete journal logs older than 2 days$ journalctl --vacuum-time=2d
Show messages by a specific executable$ journalctl [path/to/executable]
SYNOPSIS
journalctl [-b] [-p priority] [-u unit] [-n lines] [-f] [-S since] [-U until]
DESCRIPTION
journalctl queries and displays messages from the systemd journal. The journal stores log data from the kernel, system services, and applications in a structured, indexed format.
PARAMETERS
-b, --boot
Show messages from current boot (or specified boot)-p, --priority level
Filter by priority (0=emerg to 7=debug, or names)-u, --unit unit
Show messages from specified systemd unit-n, --lines n
Show the most recent n lines-f, --follow
Follow new messages as they appear-S, --since time
Show entries after specified time-U, --until time
Show entries before specified time-k, --dmesg
Show kernel messages only-r, --reverse
Reverse output (newest first)-o, --output format
Output format (short, verbose, json, cat, etc.)--vacuum-time time
Remove journal files older than time--vacuum-size size
Reduce journal to specified size-g, --grep pattern
Filter entries by regular expression (PCRE2)--no-pager
Do not pipe output into a pager--list-boots
Show a list of boot IDs with timestamps--disk-usage
Show current disk usage of journal_PID=pid
Filter by process ID_SYSTEMD_UNIT=unit
Filter by systemd unit
INSTALL
sudo apt install systemd
sudo dnf install systemd
sudo pacman -S systemd
sudo zypper install systemd
brew install systemd
nix profile install nixpkgs#systemd
CAVEATS
Journal files are stored in /var/log/journal/ (persistent) or /run/log/journal/ (volatile). Some options require root privileges.
HISTORY
Part of systemd, introduced in 2011 by Lennart Poettering. Replaces traditional syslog for systems using systemd.
