journalctl is a systemd utility same as systemctl. journalctl command is use to view the journal logs.
The Journal was developed to address problems connected with traditional logging. It is closely integrated with the rest of the system, supports various logging technologies and access management for the log files.
To check all collected logs are shown unfiltered:
An output of this command is a list of all log files generated on the system including messages generated by system components and by users.
Show all kernel logs from previous boot:
# journalctl -k -b -1
Header information of the journal fields accessed. Instead of showing journal contents, show internal header information of the journal fields accessed.
# journalctl –header
Journal disk usages of all journal files. Shows the current disk usage of all journal files.
# journalctl –disk-usage
Reduce disk usage by size, it removes the files until the disk space it use falls to the specified size, usually with “K”, “M”, “G”, “T” suffixes.
# journalctl –vacuum-size=1M
Verify journal file consistency. Check the journal file for internal consistency.
# journalctl –verify
Also read man page:
# man journalctl