Screen Locking on Sleep

This page explains what you can do to have your screen locked when the machine goes to sleep (f.ex. when you close the laptop lid). It assumes that you do not want or can't use the mechanism provided by your desktop environment (KDE, Gnome) or by the lock program (xscreensaver). As an example screen lock program, the i3lock program is used below.

Note, that both examples below require you to specify the user that will be suspending the laptop. In other words - it is not a solution for multiuser laptops. You are welcome to update this page with solutions that work with multiuser laptops. [would User=$USER work?]

When running systemd

Add a file /etc/systemd/system/i3lock.service with the following contents: 

# source: https://bbs.archlinux.org/viewtopic.php?pid=1170536#p1170536 by 65kid
#
[Unit]
Description=i3lock
Before=sleep.target

[Service]
User=the_login_of_the_user_that_suspends
Type=forking
Environment=DISPLAY=:0
ExecStart=/usr/bin/i3lock

[Install]
WantedBy=sleep.target

Now enable the service from the command line as root with: 

# systemctl enable i3lock.service

When running sysvinit

The following was working for me (TpO) on Debian wheezy under sysvinit, but stopped working on Debian jessie under systemd.

Add a file /etc/pm/sleep.d/01_screenlock with the following contents: 

#
# 01_screenlock: lock screen at suspend with i3lock
# based on http://bbs.archlinux.org/viewtopic.php?id=68158 by mokkurkalve
#

IS_ACTIVE="$( pidof i3lock )"

lock_screen() {
  # skip if i3lock is allready running
  if [ ! "$IS_ACTIVE" ]; then
       su - the_login_of_the_user_that_suspends -c "/bin/sh -c 'DISPLAY=:0.0 /usr/bin/i3lock'" &
  fi
}

case $1 in
   hibernate)
       lock_screen
       ;;
   suspend)
       lock_screen
       ;;
   thaw)
       # not required.
       ;;
   resume)
       # not required.
       ;;
   *) exit $NA
       ;;
esac