How to Set targets in RHEL/CentOS 7?

How to Set targets in RHEL/CentOS 7?

Previous versions of RHEL, which were distributed with SysV init , implemented a
predefined set of runlevels that represented specific modes of operation. These runlevels were numbered from 0 to 6. In RHEL/CentOS 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.

Runlevel Target Units Description
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.

How to get the Default Target ?
[root@dockerserver ~]# systemctl get-default
multi-user.target
[root@dockerserver ~]#

How to List all target ?
[root@dockerserver ~]# systemctl list-units --type target --all
  UNIT                   LOAD      ACTIVE   SUB    DESCRIPTION
  basic.target           loaded    active   active Basic System
  cryptsetup.target      loaded    active   active Encrypted Volumes
  emergency.target       loaded    inactive dead   Emergency Mode
  final.target           loaded    inactive dead   Final Step
  getty.target           loaded    active   active Login Prompts
  graphical.target       loaded    inactive dead   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-online.target  loaded    active   active Network is Online
  network-pre.target     loaded    inactive dead   Network (Pre)
  network.target         loaded    active   active Network
  nss-user-lookup.target loaded    inactive dead   User and Group Name Lookups
  paths.target           loaded    active   active Paths
  remote-fs-pre.target   loaded    inactive dead   Remote File Systems (Pre)
  remote-fs.target       loaded    active   active Remote File Systems
  rescue.target          loaded    inactive dead   Rescue Mode
  shutdown.target        loaded    inactive dead   Shutdown
  slices.target          loaded    active   active Slices
  sockets.target         loaded    active   active Sockets
  sound.target           loaded    active   active Sound Card
  swap.target            loaded    active   active Swap
  sysinit.target         loaded    active   active System Initialization
● syslog.target          not-found inactive dead   syslog.target
  time-sync.target       loaded    inactive dead   System Time Synchronized
  timers.target          loaded    active   active Timers
  umount.target          loaded    inactive dead   Unmount All Filesystems

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.

27 loaded units listed.

How to Change Default target?
Check the Current Runlevel or Target.
[root@Linux-box yum.repos.d]# systemctl get-default
multi-user.target
Or
Who -r


Set the Default target.
[root@Linux-box yum.repos.d]# systemctl set-default graphical.target
Removed symlink /etc/systemd/system/default.target.
Created symlink from /etc/systemd/system/default.target to /usr/lib/systemd/system/graphical.target.
[root@Linux-box yum.repos.d]#

How to change to rescue mode?
[root@dockerserver ~]# systemctl rescue
PolicyKit daemon disconnected from the bus.
We are no longer a registered authentication agent.

Broadcast message from root@dockerserver.org on pts/0 (Sat 2018-08-18 13:21:51 IST):

The system is going down to rescue mode NOW!

[root@dockerserver ~]#
How to Change current target?
[root@dockerserver ~]# systemctl isolate graphical.target
[root@dockerserver ~]#

How to Change 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 RHEL7, emergency mode requires the root password.

[root@dockerserver ~]# systemctl emergency
PolicyKit daemon disconnected from the bus.
We are no longer a registered authentication agent.