systemd
is a system and service manager. systemctl
is a main command of systemd
$ journalctl
list all running services, sockets, etc. (units).
# systemctl isolate graphical.target
analog to runlevel5 of SysV
# systemctl isolate multi-user.target
... level3
# systemctl isolate rescue.target
... level1
$ systemctl poweroff
$ systemctl reboot
# systemctl disable gdm
# systemctl enable xdm
$ systemd-cgls
$ ps xawf -eo pid,user,cgroup,args
tree view of processes belonging to services and logged-in user.
$ tree /etc/systemd/
currently used units
$ tree /lib/systemd/
all available units
# systemctl stop
terminates the running unit.
# systemctl disable
prevents activation of unit on boot, by socket or bus (or by other triggers) activation. Howerver, the unit can be started manually.
# systemct mask
or
# ln -s /dev/null /etc/systemd/system/example.service
# systemctl daemon-reload
disable unit completely (can not be started anymore).
systemd-analyze
or
journalctl --since=today | grep userspace
show the boot-up time (the time spent in the kernel before userspace has been reached).
systemd-analyze blame
print a list of all running units, ordered by the time they took to initialize.