101.3 CHANGE RUNLEVELS/BOOT TARGETS, SHUTDOWN & REBOOT

• Set the default runlevel or boot targe
• Change between runlevels/boot targets including single user mod
• Shutdown and reboot from the command line
• Alert users before switching runlevels/boot targets or other major system events
• The following is a partial list of the used files, terms and utilities:
  • □ /etc/inittab
    □ shutdown
    □ init
    □ /etc/init.d
    □ telinit
    □ system
    □ systemctl
    □ /etc/systemd/
    □ / usr/lib/system /
    □ wall

SET THE DEFAULT RUNLEVEL OR BOOT TARGET

• The init process is the first program to run at boot time
• Reads from scripts in /etc/init.d
  • SysVinit  (CentOS/RHEL 6 and earlier)
  • Upstart init daemon (Ubuntu, Fedora 9-14)
  • Systemd init daemon (CentOS/RHEL 7, Fedora 15+)
• /sbin/telinit command sends signals to init in order to change runlevels
• Runlevel-releated commands
  • systemctl get-default (Show default)
  • runlevel    (Show current runlevel)

CHANGE BETWEEN RUNLEVELS/BOOT TARGETS INCLUDING SINGLE USER MODE

• Change runlevels with systemctl, init or telinit
  • systemctl isolate graphical.target (Change runlevel w/isolation)
  • init [runlevel] or telinit [runlevel]

SysVInit Runlevel | System d Target | Description
0 | poweroff.target | Halts the system
1 | rescue.target | Single-user mode
2 | multi-user.target | Multi-user without networking
3 |multi-user.target | Multi-user with networking
4 |multi-user.target | User configurable
5 |graphical.target | Multi-user with GUI
6 |reboot.target | Reboots the system

SHUTDOWN AND REBOOT FROM THE COMMAND LINE

• Shutdown system options
  • init 0
  • telinit 0
  • shutdown
  • reboot -p (reboot w/poweroff)
  • poweroff
  • halt

• Reboot system options
  • init 6
  • telinit 6
  • shutdown -f
  • reboot [-f] (optional force option)