10.3. Working with systemd Targets

Previous versions of Red Hat Enterprise Linux, which were distributed with SysV init or Upstart, implemented a predefined set of runlevels that represented specific modes of operation. These runlevels were numbered from 0 to 6 and were defined by a selection of system services to be run when a particular runlevel was enabled by the system administrator. In Red Hat Enterprise Linux 7, the concept of runlevels has been replaced with systemd targets.
Systemd targets are represented by target units. Target units end with the .target file extension and their only purpose is to group together other systemd units through a chain of dependencies. For example, the graphical.target unit, which is used to start a graphical session, starts system services such as the GNOME Display Manager (gdm.service) or Accounts Service (accounts-daemon.service) and also activates the multi-user.target unit. Similarly, the multi-user.target unit starts other essential system services such as NetworkManager (NetworkManager.service) or D-Bus (dbus.service) and activates another target unit named basic.target.
Red Hat Enterprise Linux 7 is distributed with a number of predefined targets that are more or less similar to the standard set of runlevels from the previous releases of this system. For compatibility reasons, it also provides aliases for these targets that directly map them to SysV runlevels. Table 10.6, “Comparison of SysV Runlevels with systemd Targets” provides a complete list of SysV runlevels and their corresponding systemd targets.

Table 10.6. Comparison of SysV Runlevels with systemd Targets

RunlevelTarget UnitsDescription
0 runlevel0.target, poweroff.target Shut down and power off the system.
1 runlevel1.target, rescue.target Set up a rescue shell.
2 runlevel2.target, multi-user.target Set up a non-graphical multi-user system.
3 runlevel3.target, multi-user.target Set up a non-graphical multi-user system.
4 runlevel4.target, multi-user.target Set up a non-graphical multi-user system.
5 runlevel5.target, graphical.target Set up a graphical multi-user system.
6 runlevel6.target, reboot.target Shut down and reboot the system.
To view, change, or configure systemd targets, use the systemctl utility as described in Table 10.7, “Comparison of SysV init Commands with systemctl” and in the sections below. The runlevel and telinit commands are still available in the system and work as expected, but are only included for compatibility reasons and should be avoided.

Table 10.7. Comparison of SysV init Commands with systemctl

Old CommandNew CommandDescription
runlevel systemctl list-units --type target Lists currently loaded target units.
telinit runlevel systemctl isolate name.target Changes the current target.

10.3.1. Viewing the Default Target

To determine which target unit is used by default, run the following command: 
systemctl get-default
This command resolves the symbolic link located at /etc/systemd/system/default.target and displays the result. For information on how to change the default target, see Section 10.3.3, “Changing the Default Target”. For information on how to list all currently loaded target units, see Section 10.3.2, “Viewing the Current Target”.

Example 10.10. Viewing the Default Target

To display the default target unit, type: 
~]$ systemctl get-default
graphical.target

10.3.2. Viewing the Current Target

To list all currently loaded target units, type the following command at a shell prompt: 
systemctl list-units --type target
For each target unit, this commands displays its full name (UNIT) followed by a note whether the unit has been loaded (LOAD), its high-level (ACTIVE) and low-level (SUB) unit activation state, and a short description (DESCRIPTION).
By default, the systemctl list-units command displays only active units. If you want to list all loaded units regardless of their state, run this command with the --all or -a command line option: 
systemctl list-units --type target --all
See Section 10.3.1, “Viewing the Default Target” for information on how to display the default target. For information on how to change the current target, see Section 10.3.4, “Changing the Current Target”.

Example 10.11. Viewing the Current Target

To list all currently loaded target units, run the following command: 
~]$ systemctl list-units --type target
UNIT                  LOAD   ACTIVE SUB    DESCRIPTION
basic.target          loaded active active Basic System
cryptsetup.target     loaded active active Encrypted Volumes
getty.target          loaded active active Login Prompts
graphical.target      loaded active active Graphical Interface
local-fs-pre.target   loaded active active Local File Systems (Pre)
local-fs.target       loaded active active Local File Systems
multi-user.target     loaded active active Multi-User System
network.target        loaded active active Network
paths.target          loaded active active Paths
remote-fs.target      loaded active active Remote File Systems
sockets.target        loaded active active Sockets
sound.target          loaded active active Sound Card
spice-vdagentd.target loaded active active Agent daemon for Spice guests
swap.target           loaded active active Swap
sysinit.target        loaded active active System Initialization
time-sync.target      loaded active active System Time Synchronized
timers.target         loaded active active Timers

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.

17 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.

10.3.3. Changing the Default Target

To configure the system to use a different target unit by default, type the following at a shell prompt as root: 
systemctl set-default name.target
Replace name with the name of the target unit you want to use by default (for example, multi-user). This command replaces the /etc/systemd/system/default.target file with a symbolic link to /usr/lib/systemd/system/name.target, where name is the name of the target unit you want to use. For information on how to change the current target, see Section 10.3.4, “Changing the Current Target”. For information on how to list all currently loaded target units, see Section 10.3.2, “Viewing the Current Target”.

Example 10.12. Changing the Default Target

To configure the system to use the multi-user.target unit by default, run the following command as root: 
~]# systemctl set-default multi-user.target
rm '/etc/systemd/system/default.target'
ln -s '/usr/lib/systemd/system/multi-user.target' '/etc/systemd/system/default.target'

10.3.4. Changing the Current Target

To change to a different target unit in the current session, type the following at a shell prompt as root: 
systemctl isolate name.target
Replace name with the name of the target unit you want to use (for example, multi-user). This command starts the target unit named name and all dependent units, and immediately stops all others. For information on how to change the default target, see Section 10.3.3, “Changing the Default Target”. For information on how to list all currently loaded target units, see Section 10.3.2, “Viewing the Current Target”.

Example 10.13. Changing the Current Target

To turn off the graphical user interface and change to the multi-user.target unit in the current session, run the following command as root: 
~]# systemctl isolate multi-user.target

10.3.5. Changing to Rescue Mode

Rescue mode provides a convenient single-user environment and allows you to repair your system in situations when it is unable to complete a regular booting process. In rescue mode, the system attempts to mount all local file systems and start some important system services, but it does not activate network interfaces or allow more users to be logged into the system at the same time. In Red Hat Enterprise Linux 7, rescue mode is equivalent to single user mode and requires the root password.
To change the current target and enter rescue mode in the current session, type the following at a shell prompt as root: 
systemctl rescue
This command is similar to systemctl isolate rescue.target, but it also sends an informative message to all users that are currently logged into the system. To prevent systemd from sending this message, run this command with the --no-wall command line option: 
systemctl --no-wall rescue
For information on how to enter emergency mode, see Section 10.3.6, “Changing to Emergency Mode”.

Example 10.14. Changing to Rescue Mode

To enter rescue mode in the current session, run the following command as root: 
~]# systemctl rescue

Broadcast message from root@localhost on pts/0 (Fri 2013-10-25 18:23:15 CEST):

The system is going down to rescue mode NOW!

10.3.6. Changing to Emergency Mode

Emergency mode provides the most minimal environment possible and allows you to repair your system even in situations when the system is unable to enter rescue mode. In emergency mode, the system mounts the root file system only for reading, does not attempt to mount any other local file systems, does not activate network interfaces, and only starts a few essential services. In Red Hat Enterprise Linux 7, emergency mode requires the root password.
To change the current target and enter emergency mode, type the following at a shell prompt as root: 
systemctl emergency
This command is similar to systemctl isolate emergency.target, but it also sends an informative message to all users that are currently logged into the system. To prevent systemd from sending this message, run this command with the --no-wall command line option: 
systemctl --no-wall emergency
For information on how to enter rescue mode, see Section 10.3.5, “Changing to Rescue Mode”.

Example 10.15. Changing to Emergency Mode

To enter emergency mode without sending a message to all users that are currently logged into the system, run the following command as root: 
~]# systemctl --no-wall emergency