halt command in Linux with examples

This command in Linux is used to instruct the hardware to stop all the CPU functions. Basically, it reboots or stops the system. If the system is in runlevel 0 or 6 or using the command with –force option, it results in rebooting of the system otherwise it results in shutdown.

Syntax:

halt [OPTION]...

Options:

OPTION	DESCRIPTION
-f, –force	It does not invoke shutdown.
-w, –wtmp-only	It will not call shutdown or the reboot system call but writes the shutdown record to /var/log/wtmp file.
-p, –poweroff	To behave as poweroff
–verbose	Gives verbose messages when reebooting which helps in debugging problems with shutdown.

Files:

◈ /var/log/wtmp : Consists a new runlevel record for the shutdown time.

◈ /var/run/utmp : Gets updated by a shutdown time record when the current runlevel will be read.

Example 1: To cease all CPU function on the system.

$halt

Output:

Broadcast message from ubuntu@ubuntu

root@ubuntu:/var/log# (/dev/pts/0) at 10:15...

The system is going down for halt NOW.

Example 2: To power off the system using halt command.

$halt -p

Output:

Broadcast message from ubuntu@ubuntu

(/dev/pts/0) at 10:16...

The system is going down for power off NOW.

Example 3: halt command with -w option to write shutdown record.

$halt -w

Note: For this, there will be no output on the screen.