To 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. For example this would take you to single user mode
# shutdown now
To 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.
# shutdown −h now
To broad−casted the message to all users, for example.
# shutdown −h now “Warning system malfunction, self−destruct imminent“
To Shut down at a particular time.
# shutdown −h 11:50
To Reboot at a particular time
# shutdown −r 11:50
Shutdown −h vs poweroff
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
To reboot the Linux system
# shutdown −r now
Shutdown ( −r = reboot) the computer immediately. It begins the reboot procedure, press CTRL−C to break it.
To reboot with a message.
# shutdown −r now “Warning system rebooting, all files will be destroyed”
Same as the shutdown −r now the following command works soft rebooting the system
May be used from a terminal to reboot or shutdown, it depends on your system configuration. Note that this doesn’t work from an xterminal. CTRL−ALT−DEL begins the reboot/shutdown immediately, the user does not have to be logged in.
To disable CTRL−ALT−DEL from rebooting your computer (or to have it do something different), you can edit the/etc/inittab file (as root).
ca::ctrlaltdel:/sbin/shutdown −t3 −r now
You could also change the command it runs for example if you changed the −r to a −h the computer would turn off instead of rebooting, or you could have it do anything you want. It’s up to your creativity to make it do something interesting.
Hard-way of shutdown / rebooting
We can do this by making use of the kernels sysrq-trigger magical key. WARNING : Following may lead to data loss or file system corruption so use at your own risk.
Enable the sysrq-trigger kernel variable.
# echo 1 > /proc/sys/kernel/sysrq
And then use the following command to trigger the hard reboot.
# echo b > /proc/sysrq-trigger
To shutdown the system instently
# echo o > /proc/sysrq-trigger
Always use sync command before trying the above options.