Systemd

Build dependency graph. The package graphviz is required.

systemd-analyze dot | dot -Tsvg > systemd.svg

Show the systemd configuration paths (with precedence)

systemctl -p UnitPath show

List cgroups with

systemd-cgls

List jobs

systemctl list-jobs

Show properties of a unit or only a specific property of a unit

systemctl show unit
systemctl show -p type unit

For example, sshd is wanted by multi-user.target

$ systemctl show -p WantedBy sshd
WantedBy=multi-user.target

Unit types

Type= is one of

Type	Description
simple	TODO
forking
notify
dbus
oneshot
idle

Dependencies

Wants should be the default because the actual unit will not fail even if the dependency fails which results in a more robust system.

Keyword	Description
Requires	strict. If dependency fails the, unit fails.
Wants	If dependency fails, the unit is still activated.
Requisite	Dependency must already be running, otherwise the unit fails to activate.
Conflicts	The conflicted unit is deactivated if it's active. A simultaneous activation of conflicting units fails.

Instead of specifying a direct dependency in the unit itself, a dependency for a unit can also be specified in another unit (so in the dependency unit). This offers the advantage that when new units are added, only this new unit has to be edited and can specify itself as a dependency for an existing unit without modyfing that existing unit.

Keyword	Description
WantedBy	See Wants. if this dependency fails, the other unit is still activated.
RequiredBy	See Requires. A strict dependency.

TODO: unit types explanation TODO: p143 specifiers