====== Boot Systems Into Different Targets Manually ======

**General Information**

There are no longer runlevels; systemd uses "targets". 

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===== Systemd Units =====

Unit configuration file locations
  * /usr/lib/systemd/system => system unit configuration files (default with system)
  * /etc/systemd/system => additional configuration files (downloaded or custom)

\\
Show available unit types
<code bash>
systemctl -t help
</code>

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===== Systemd Targets =====

Some common targets
  * poweroff.target => power off the system
  * emergency.target => single user (root), root file system mounted, do not mount any other file systems, no network services.
    * Used if the system cannot be repaired in rescue.target
  * rescue.target => single user environment (root), mount local file systems, with minimum services loaded, no network services.
  * multi-user.target => Multi-user non-graphical, with all file systems and networking
  * graphical.target => GUI environment, multi-user, with all file systems and networking
  * reboot.target => reboot the system

\\
What targets are currently active?
<code bash>
systemctl -t target
</code>
  * Look for either emergency, rescue, multi-user, or graphical.
  * **Note**: If you are in the graphical target, multi-user will also be active, since multi-user is a dependency of graphical.

\\
Current default target
<code bash>
systemctl get-default
</code>

\\
Set default to graphical target
<code bash>
systemctl set-default graphical.target
</code>

\\
List loaded unit files (systemctl) of type target (--type=target) whether they are active or not (--all)
<code bash>
systemctl --type=target --all
</code>
  * systemctl list-units => "list-units" is the default command to systemctl if none specified
  * --type=target => show loaded, active units of the target type
  * --all => show all loaded unit files, even if they are not active

\\
List all installed unit files on the system
<code bash>
systemctl list-unit-files
</code>

\\
View a target's dependencies
<code bash>
systemctl list-dependencies multi-user.target
</code>
  * List what will start upon entering multi-user.target

\\
Move from graphical target to multi-user (command prompt)
<code bash>
systemctl isolate multi-user.target
</code>
  * Stops all GUI services, goes to command line login prompt

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===== Other Systemctl Commands =====

**Note:** By default, systemctl commands will only show the active configuration files unless you pass the "--all" option

  * systemctl --type=service => list all loaded and active only service unit config files
  * systemctl --type=service --all => list all loaded and active or inactive units
  * systemctl is-active servicename => check if service is active or inactive
  * systemctl is-enabled servicename => check if service is enabled or disabled 
  * systemctl --failed --type=service => list all failed services
  * systemctl list-unit-files --type=service => view enabled and disabled settings for all units installed on the OS of the service type

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===== Boot to rescue mode =====

To boot to something other than the default target, such as the rescue target, during boot:
  - Interrupt boot process at grub menu
  - Press "e" to edit the boot entry
  - Navigate to the "linux16" kernel entry
  - Append "systemd.unit=rescue.target"
  - Ctrl+x to continue boot process

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