Systemd is a system and service manager for Linux, compatible with SysV and LSB init scripts. Systemd provides:
* Aggressive parallelization capabilities
* Uses socket and D-Bus activation for starting services
* Offers on-demand starting of daemons, keeps track of processes using Linux cgroups
* Supports snapshotting and restoring of the system state
* Maintains mount and automount points
* Implements an elaborate transactional dependency-based service control logic.
The `systemctl` command is the primary tool to manage Systemd. It combines the functionality of SysVinit's `service` and `chkconfig` commands into a single tool you can use to enable and disable services permanently or only for the current session.
Systemd manages _units_, which are representations of system resources and services. This following list shows the unit types that Systemd can manage:
service::
A service on the system, including instructions for starting, restarting, and stopping the service.
socket::
A network socket associated with a service.
device::
A device specifically managed with Systemd.
mount::
A mountpoint managed with Systemd.
automount::
A mountpoint automatically mounted on boot.
swap::
Swap space on the system.
target::
A synchronization point for other units. Usually used to start enabled services on boot.
path::
A path for path-based activation. For example, you can start services based on the state of a certain path, such as whether it exists or not.
timer::
A timer to schedule activation of another unit.
snapshot::
A snapshot of the current Systemd state. Usually used to rollback after making temporary changes to Systemd.
slice::
Restrivtion of resources through Linux Control Group nodes (cgroups).
