systemctl

Question 1

systemctl

Help pages 1-2

Answer 1

systemd is a Linux initialization system and service manager that includes features like parallel initialization, on-demand starting of daemons, mount and automount point maintenance, snapshot support, and processes tracking using Linux control groups. systemd provides a logging daemon and other tools and utilities to help with common system administration tasks.

Question 2

systemctl

Help page 3

Answer 2

systemd is commonly used like:

systemctl start application.service

systemctl stop application.service

Question 3

systemctl stop application.service

systemctl start application.service

systemctl reload application.service

systemctl status application.service

systemctl restart application.service

systemctl enable application.service

systemctl disable application.service

Answer 3

stop, Stops an application

start, Starts an application

reload, Asks an application to reload its configuration

status, Show terse runtime status information about application

restart, Stops and starts an application

enable, Enables an application by adding symlinks to the units Install directory thus allowing it to start at boot

disable, Disables the application from starting at boot via removing the symlinks

Question 4

systemctl is-active application.service

systemctl is-enabled application.service

systemctl is-failed application.service

Answer 4

is-active, Returns the current unit state active or inactive, an exit code of 0 will be used for active

is-enabled, Outputs whether a service is enabled or disabled and an exit code of 0 will be used for enabled

is-failed, Checks whether the specified unit is in a failed state, returns an exit code of 0 if it is failed.

Question 5

systemctl list-units

Answer 5

Lists all active units the systemd knows about.

The output has the following columns:

UNIT: The systemd unit name

LOAD: Whether the unit’s configuration has been parsed by systemd. The configuration of loaded units is kept in memory.

ACTIVE: A summary state about whether the unit is active. This is usually a fairly basic way to tell if the unit has started successfully or not.

SUB: This is a lower-level state that indicates more detailed information about the unit. This often varies by unit type, state, and the actual method in which the unit runs.

DESCRIPTION: A short textual description of what the unit is/does.

Question 6

systemctl list-units –all

Answer 6

This shows any and all units that have been loaded or attempted to load regardless of their state.