Merge journals from a directory journalctl
Read journals from another root (rescue/forensics) without copying files in
journalctl -D /mnt/crashed/var/log/journal -b -1 -p err
more journalctl
all 12 commands →
Verify persistent storage is enabled
journalctl --header | grep -iE 'file|state'; ls -d /var/log/journal 2>/dev/null || echo volatile
Filter by priority error and above
journalctl -p err -b --no-pager
Match by raw systemd unit field
journalctl _SYSTEMD_UNIT=sshd.service --since today
Combine field filters with OR
journalctl _PID=1 + _COMM=sshd -o short-iso
Regex grep across messages
journalctl --grep='oom|out of memory' --case-sensitive=false -b