I have desktop edition of Ubuntu.
I like the Terminal so that that I prefer to shutdown my computer with the shutdown command.
However when I type shutdown now it prompts me to enter my password.Is there any way I can shutdown my computer using this command without entering my password?
Open up a terminal (CTRL + T)
and type the following sudo visudo
Add the following line:
%group_name ALL=(ALL) NOPASSWD: /sbin/poweroff, /sbin/reboot, /sbin/shutdown
or
user_name ALL=(ALL) NOPASSWD: /sbin/poweroff, /sbin/reboot, /sbin/shutdown
This allows the user/group to run the above three commands, using sudo, however with no password.
So, sudo poweroff will now result in a passwordless shutdown.
However, to make this even cleaner, we'll add an alias, so that running shutdown calls sudo shutdown now.
Open ~/.bash_aliases for editing.
nano ~/.bash_aliases
Insert the following line at the end of the file:
alias shutdown='sudo shutdown now'
Finally, load the changes to the .bash_aliases file...
source ~/.bash_aliases
Try it out!
shutdown
Thanks, Eric.
A safe way to do this without using sudo and without tinkering with the system, is by executing these one-liner commands:
(This is due to Ubuntu's shift in using systemd instead of Upstart)
systemctl poweroff
systemctl reboot
systemctl suspend
systemctl hibernate
systemctl hybrid-sleep
Since hibernate is normally disabled by default in Ubuntu systems, you can enable this by checking this answer. Original source here.
Shutdown:
/usr/bin/dbus-send --system --print-reply --dest="org.freedesktop.ConsoleKit" /org/freedesktop/ConsoleKit/Manager org.freedesktop.ConsoleKit.Manager.Stop
Restart:
/usr/bin/dbus-send --system --print-reply --dest="org.freedesktop.ConsoleKit" /org/freedesktop/ConsoleKit/Manager org.freedesktop.ConsoleKit.Manager.Restart
consolekit 
should of course be installed your system.
Other commands you may like:
Suspend:
/usr/bin/dbus-send --system --print-reply --dest="org.freedesktop.UPower" /org/freedesktop/UPower org.freedesktop.UPower.Suspend
Hibernate: (if enabled on your system)
/usr/bin/dbus-send --system --print-reply --dest="org.freedesktop.UPower" /org/freedesktop/UPower org.freedesktop.UPower.Hibernate
unity uses many gnome services, and in that case too - you can shutdown gnome way.
gnome-session-quit --power-off --force --no-prompt
will do the job.
On Ubuntu 20.04 LTS, I created a polkit file with
echo "[Shutdown or suspend without a password]
Identity=unix-user:$USER
Action=org.freedesktop.login1.set-wall-message;org.freedesktop.login1.halt;org.freedesktop.login1.suspend
ResultAny=yes
" | sudo tee /etc/polkit-1/localauthority/50-local.d/allow_shutdown_suspend.pkla
With this, systemctl halt and systemctl suspend work without a password. This also work remotely with e.g. ssh 192.168.0.55 -t 'systemctl suspend'.
While you can use the method of allowing NOPASSWD on /usr/sbin/shutdown, although another, DE-independent solution is to just use init 0.
