How do I lock the screen from a terminal? [duplicate]

Simple:

gnome-screensaver-command -l

The following can also work, if the screensaver is set to lock when activate (see screensaver settings), since the command activates the screensaver:

gnome-screensaver-command -a

You can add an alias to the command by editing the file .bashrc (or .bash_aliases) in your home directory:

gedit $HOME/.bashrc

and adding the following line:

alias lock='gnome-screensaver-command -l'

Then from terminal:

source .profile

This will activate the alias. From now on, the alias lock in a terminal will have the effect of locking the screen.

In addition to what January said, this also works:

gnome-screensaver-command --lock

or

gnome-screensaver-command -l

According to the gnome-screensaver-command man page...

-l, --lock                 Tells the running screensaver process to lock the screen immediately
-a, --activate             Turn the screensaver on (blank the screen)

For further clarification, here is another question/answer (also by January) which describes the differences between invoking the lock and activating your screensaver:

Difference between gnome-screensaver-command -a and gnome-screensaver-command -l

Starting in Ubuntu 14.04, Unity's lock screen no longer uses gnome-screensaver. The command gnome-screensaver-command -l will still work in most cases, but see this question for exceptions.

If that command does not work (say, for instance, that gnome-screensaver is not installed), bringing up the proper Unity lock screen (not the greeter where you can switch users) can be done via this command in a terminal:

dbus-send --type=method_call --dest=org.gnome.ScreenSaver /org/gnome/ScreenSaver org.gnome.ScreenSaver.Lock

Please install vlock. Then you can switch to a VT (text terminal, using Ctrl+Alt+F1) and run

vlock -a -s

This works whether you have X11 running or not.

$!(sleep 10s ;  xset dpms force suspend) & xdg-screensaver lock

this starts the screen saver in locked mode and then puts your display in standby. sweet and simple, no sudo. command line or shell script works fine. i use this for a keyboard hotkey. Ubuntu Mate 15.10

In case that you need to lock the screen on a terminal in a non-GUI environment you could make use of screen

While in screen press the following key combinations to lock the terminal.

Ctrl + a

Ctrl + x

In my case xdg-screensaver lock is works perfectly fine. Also I save it by the setting or when I press window+L it will lock the screen immediately

For LightDM users, try dm-tool switch-to-greeter.

A dirty hack of using the shortcut Ctrl+Alt+L for the locking the screen from a terminal:

1. Install xdotool from the software center or from the terminal as follows:

   sudo apt-get install xdotool
   

2. Type the following to lock the screen from the terminal:

   xdotool key Ctrl+alt+l
   

Refer to the manual page for xdotool for more.

It depends on your display manager. I have lightdm, I can do dm-tool lock to bring up a lock screen. It's not really secure, though, I found an easy way to bypass it.