Shutting Down and Rebooting the System

Command Line

1. Shutdown the computer immediately (don't power down). Note that in UNIX systems this kind of shutdown means to go to "single-user mode". Single-user mode is a mode where only the administrator (root) has access to the computer, this mode is designed for maintenance and is often used for repairs.

   [root@myserver ~]# shutdown now
   
   /sbin/shutdown [-t sec] [-arkhncfFHP] time [warning-message]
   OPTIONS
   -a     Use /etc/shutdown.allow.
   -t sec Tell init to wait sec seconds between sending processes the warning and the kill signal, before changing to another run-level.
   -k     Don't really shutdown; only send the warning messages to everybody.
   -r     Reboot after shutdown.
   -h     Halt or poweroff after shutdown.
   -H     Halt action is to halt or drop into boot monitor on systems that support it.
   -P     Halt action is to turn off the power.
   -n     [DEPRECATED] Don't call init to do the shutdown but do it ourself. The use of this option is discouraged, and  its results are not always what you'd expect.
   -f     Skip fsck on reboot.
   -F     Force fsck on reboot.
   -c     Cancel an already running shutdown. With this option it is of course not possible to give the time argument, but you can enter a explanatory message on the command line that will be sent to all users.
    time   When to shutdown.
    warning-message  Message to send to all users.
   
     

2. Shutdown (-h = halt) the computer immediately. It begins the shutdown procedure, press CTRL-C (break-key) to stop it. After the end of the command you can also leave a message in quotation marks which will be broad-casted to all users.

   [root@myserver ~]# shutdown -h now "Warning system malfunction, self-destruct imminent"
     

3. On some systems, shutdown -h and halt do not actually turn the system's power off. On systems that do not power off with these commands use the poweroff command halt

   [root@myserver ~]# poweroff
   
   /sbin/poweroff [-n] [-w] [-d] [-f] [-i] [-h]
   OPTIONS
   -n     Don't sync before reboot or halt. Note that the kernel and storage drivers may still sync.
   -w     Don't actually reboot or halt but only write the wtmp record (in the /var/log/wtmp file).
   -d     Don't write the wtmp record. The -n flag implies -d.
   -f     Force halt or reboot, don't call shutdown.
   -i     Shut down all network interfaces just before halt or reboot.
   -h     Put all harddrives on the system in standby mode just before halt or poweroff.
        

4. Shutting down at a particular time

   [root@myserver ~]# shutdown -h 16:16
     

5. Shutdown ( -r = reboot) the computer immediately. It begins the reboot procedure, press CTRL-C (break-key) to stop it. After the end of the command you can also leave a message in quotation marks which will be broad-casted to all users.

   [root@myserver ~]# shutdown -r now "Warning system rebooting, all files will be destroyed"
   
   [root@myserver ~]# reboot
   
    /sbin/reboot [-n] [-w] [-d] [-f] [-i]
   OPTIONS
   -n     Don't sync before reboot or halt. Note that the kernel and storage drivers may still sync.
   -w     Don't actually reboot or halt but only write the wtmp record (in the /var/log/wtmp file).
   -d     Don't write the wtmp record. The -n flag implies -d.
   -f     Force halt or reboot, don't call shutdown.
   -i     Shut down all network interfaces just before halt or reboot.
     

6. Rebooting at a particular time

   [root@myserver ~]# shutdown -r 16:16
     

GUI

1. Shutdown: go to System => Shut down the computer or click Shut Down on log in screen.
2. Log out from the system: go to System => Log out [username] of this session to log in as a different user
3. Restart: click Restart on log in screen.

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Refer to:	redhat.com: Shutting Down/Rebooting the System
	cyberciti.biz: Linux Reboot Command Example