buttslock will lock your screen when your machine goes to sleep

buttslock/Dockerfile

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+#
+# This container will listen to DBus events to be notified when your
+# computer goes to sleep. When such events happen, it will lock the
+# screen with a fancy lock.
+#
+# It needs to be started with a few bind-mounts:
+# - /etc/passwd, /etc/shadow (read-only)
+# - /var/run/dbus, the X11 socket (typically /tmp/.X11-unix)
+# And it also requires the USER and DISPLAY environment variables to be set.
+#
+FROM alpine
+RUN apk update
+RUN apk add i3lock imagemagick py-dbus py-gobject scrot ttf-liberation xkeyboard-config
+ADD buttslock.py buttslock.sh lock.png /
+CMD /buttslock.py

buttslock/buttslock.py

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+#!/usr/bin/env python
+
+# Shamelessly pasted from:
+# http://serverfault.com/questions/573379/system-suspend-dbus-upower-signals-are-not-seen
+
+from datetime import datetime
+import dbus
+import gobject
+from dbus.mainloop.glib import DBusGMainLoop
+import os
+
+def handle_sleep(*args):
+    print "%s    PrepareForSleep%s" % (datetime.now().ctime(), args)
+    if len(args)>0 and args[0]:
+        os.system("/buttslock.sh")
+
+DBusGMainLoop(set_as_default=True)     # integrate into gobject main loop
+bus = dbus.SystemBus()                 # connect to system wide dbus
+bus.add_signal_receiver(               # define the signal to listen to
+    handle_sleep,                      # callback function
+    'PrepareForSleep',                 # signal name
+    'org.freedesktop.login1.Manager',  # interface
+    'org.freedesktop.login1'           # bus name
+)
+
+loop = gobject.MainLoop()
+loop.run()
+

buttslock/buttslock.sh

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+#!/bin/sh
+
+# Shamelessly copied from:
+# https://github.com/meskarune/i3lock-fancy
+
+# All options are here: http://www.imagemagick.org/Usage/blur/#blur_args
+#BLURTYPE="0x5" # 7.52s
+#BLURTYPE="0x2" # 4.39s
+#BLURTYPE="5x3" # 3.80s
+BLURTYPE="2x8" # 2.90s
+#BLURTYPE="2x3" # 2.92s
+
+# I still have to figure out how to get imagemagick fonts to work in Alpine
+#FONT="-font Liberation-Sans"
+FONT=
+
+scrot /tmp/scrot.png
+convert /tmp/scrot.png \
+    -level 0%,100%,0.6 -blur $BLURTYPE $FONT \
+    -pointsize 26 -fill white -gravity center \
+    -annotate +0+200 'Type password to unlock' \
+    /tmp/conv.png
+composite -gravity center /lock.png /tmp/conv.png /tmp/lock.png
+#i3lock --textcolor=ffffff00 --insidecolor=ffffff1c --ringcolor=ffffff3e --linecolor=ffffff00 --keyhlcolor=00000080 --ringvercolor=00000000 --insidevercolor=0000001c --ringwrongcolor=00000055 --insidewrongcolor=0000001c  -i $IMAGE
+i3lock -i /tmp/lock.png --ignore-empty-password
+