Difference between revisions of "Systemd"

Revision as of 02:08, 14 May 2015

systemd is a suite of system management daemons, libraries, and utilities designed as a central management and configuration platform for the Linux computer operating system.

Example usage

• Check if you are running "init" or "systemd":

$ cat /proc/1/comm
systemd

• Restart network:

$ systemctl restart network.target

• stop and mask the firewalld service (see: iptables vs. firewalld):

$ systemctl stop firewalld
$ systemctl mask firewalld

• Miscellaneous:

$ systemctl list-units
$ systemctl list-units -t service
$ systemctl list-units | grep .service
$ systemctl list-units -t target
$ systemctl list-unit-files
$ systemctl list-unit-files -t target
$ systemctl list-dependencies multi-user.target
$ systemctl [status|stop|enable|disable|restart] ssh.service
$ systemctl is-enabled ssh.service
$ systemctl [reboot|poweroff|suspend]

$ systemctl --failed
  UNIT              LOAD   ACTIVE SUB    DESCRIPTION
● pollinate.service loaded failed failed Seed the pseudo random number generator on first boot
● vboxadd.service   loaded failed failed LSB: VirtualBox Linux Additions kernel modules
LOAD   = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB    = The low-level unit activation state, values depend on unit type.

• cgroup tree

$ systemd-cgls
├─1 /sbin/init
├─system.slice
│ ├─dbus.service
│ │ └─776 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
│ ├─cron.service
│ │ └─692 /usr/sbin/cron -f
...

• ps with cgroups:

$ alias psc='ps xawf -eo pid,user,cgroup,args'

systemd-analyze

• Analyze system boot-up performance

$ systemd-analyze
Startup finished in 5.223s (kernel) + 7.781s (userspace) = 13.004s

• Plot all dependencies of any unit whose name starts with "avahi-daemon":

$ systemd-analyze dot 'avahi-daemon.*' | dot -Tsvg > avahi.svg
$ eog avahi.svg

• Plot the dependencies between all known target units:

$ systemd-analyze dot --to-pattern='*.target' --from-pattern='*.target' | dot -Tsvg > targets.svg
$ eog targets.svg

journalctl

Note: combine with syslog-ng for backward compatibility.

$ journalctl
$ journalctl | grep -Ei 'error|fail'
$ journalctl -b  # show only logs from this boot
$ journalctl -b -1 # show only logs from previous boot
$ journalctl -u ssh  # show only logs for a given unit
$ journalctl -f  # follow (somewhat analogous to `tail -f /var/log/messages`)
$ journalctl -f -u ssh.service  # show only logs for ssh unit and follow

timedatectl

Note: Most of these commands will need to be run as either root or sudo and is only valid for systems using systemd.

• List all available timezones on your computer/server:

$ timedatectl list-timezones

• Set your computer's/server's timezone:

$ timedatectl set-timezone region/timezone

• For instance, to set your timezone to United States Pacific Time (PST; -8GMT):

$ timedatectl set-timezone America/Vancouver

Your system will be updated to use the selected timezone. You can verify with:

$ timedatectl

      Local time: Fri, 2012-11-02 09:26:46 CET
  Universal time: Fri, 2012-11-02 08:26:46 UTC
        RTC time: Fri, 2012-11-02 08:26:45
        Timezone: Europe/Warsaw
      UTC offset: +0100
     NTP enabled: no
NTP synchronized: no
 RTC in local TZ: no
      DST active: no
 Last DST change: CEST → CET, DST became inactive
      Sun, 2012-10-28 02:59:59 CEST
      Sun, 2012-10-28 02:00:00 CET
 Next DST change: CET → CEST, DST will become active
      the clock will jump one hour forward
      Sun, 2013-03-31 01:59:59 CET
      Sun, 2013-03-31 03:00:00 CEST

• Enable an NTP daemon (chronyd):

$ timedatectl set-ntp true
==== AUTHENTICATING FOR org.freedesktop.timedate1.set-ntp ===
Authentication is required to control whether network time synchronization shall be enabled.
Authenticating as: user
Password: ********
==== AUTHENTICATION COMPLETE ===

$ systemctl status chronyd.service
chronyd.service - NTP client/server
Loaded: loaded (/lib/systemd/system/chronyd.service; enabled)
Active: active (running) since Fri, 2012-11-02 09:36:25 CET; 5s ago
...

External links

• Official website