systemctl tips

gistfile1.txt

Source: https://www.digitalocean.com/community/tutorials/how-to-use-journalctl-to-view-and-manipulate-systemd-logs

# most recently used/needed: journalctl -u nginx.service
# kernel messages (the same as dmesg -T?): journalctl -k
# monitoring journalctl -f, journalctl -n 20, 

journalctl --utc
# since most recent re/boot
journalctl -b
# 
journalctl --list-boots
# logs from  previous boot
journalctl -b -1

# config /etc/systemd/journald.conf
[Journal]
Storage=persistent

# about systemtime
timedatectl list-timezones
timedatectl set-timezone zone
# displays local time, utc, timezone, NTP sync status
timedatectl status

journalctl --since "2015-01-10" --until "2015-01-11 03:00"
journalctl --since 09:00 --until "1 hour ago"

journalctl -u nginx.service --since today
journalctl -u nginx.service -u php-fpm.service --since today
journalctl _UID=33 --since today
man systemd.journal-fields

journalctl -k
# kernel messages 5 boots ago
journalctl -k -b -5
# only err
journalctl -p err -b

    0: emerg
    1: alert
    2: crit
    3: err
    4: warning
    5: notice
    6: info
    7: debug

journalclt --no-pager
# prints unprintable characters

# using json
journalctl -b -u nginx -o json
journalctl -b -u nginx -o json-pretty

journalctl -a

# disk size
journalctl --disk-usage
journalctl --vacuum-size=1G
journalctl --vacuum-time=1years
# limit journal expansion: /etc/systemd/journald.conf 
    SystemMaxUse=: Specifies the maximum disk space that can be used by the journal in persistent storage.
    SystemKeepFree=: Specifies the amount of space that the journal should leave free when adding journal entries to persistent storage.
    SystemMaxFileSize=: Controls how large individual journal files can grow to in persistent storage before being rotated.
    RuntimeMaxUse=: Specifies the maximum disk space that can be used in volatile storage (within the /run filesystem).
    RuntimeKeepFree=: Specifies the amount of space to be set aside for other uses when writing data to volatile storage (within the /run filesystem).
    RuntimeMaxFileSize=: Specifies the amount of space that an individual journal file can take up in volatile storage (within the /run filesystem) before being rotated.