Archlinux i3-wm on a docking station

Written 03 Jul 2017 by Sergei Turukin

I’m using Archlinux with i3 tiling window manager. On the hardware side, this laptop sometimes sits on a docking station with external monitor attached to it. Periodically, I take it away from my desk to work in a different environment. Here are several tips’n’tricks I found useful.

Monitor hotplugging

First thing that is really convenient is to automate monitor setup. It is either one laptop screen or a combination of laptop and external monitor.

There are lots of recipes on the internet that employ udev rules and custom shell scripts. I won’t suggest any novel ideas andjust share my solution with description and some problems workarounds.

First, here is udev rule (place it into `/etc/udev/rules.d/*.conf):

KERNEL=="card0", ACTION=="change", SUBSYSTEM=="drm", ENV{DISPLAY}=":0", ENV{XAUTHORITY}="/home/USERNAME/.Xauthority", RUN+="/home/USERNAME/bin/hotplug
_monitor.sh"

Some things to note:

1. Replace USERNAME with actual username
2. Use udevadm monitor to monitor events and tweak KERNEL variable as needed (could be card1, for example)
3. XAuthority file location could different, check your distro
4. Call udevadm control --reload-rules after any changes to the file

Adding this rule will call specified script on every plug/unplug event. Here is my sample script:

#!/usr/bin/bash

export DISPLAY=:0
export XAUTHORITY=/home/USERNAME/.Xauthority

set -e
MONITOR='DP-3'

function wait_for_monitor {
    xrandr | grep $MONITOR | grep '\bconnected'
    while [ $? -ne 0 ]; do
            logger -t "waiting for 100ms"
            sleep 0.1
            xrandr | grep $MONITOR | grep '\bconnected'
    done
 }

EXTERNAL_MONITOR_STATUS=$(cat /sys/class/drm/card0-$MONITOR/status )
if [ $EXTERNAL_MONITOR_STATUS  == "connected" ]; then
    wait_for_monitor
    xrandr --output $MONITOR --auto --primary --output LVDS-1 --auto --left-of $MONITOR
    /home/USERNAME/bin/i3plug.py restore
else
    /home/USERNAME/bin/i3plug.py save
    xrandr --output $MONITOR --off
fi

feh --bg-scale /home/USERNAME/wallpaper.jpg

Pretty simple: it checks specified monitor status and applies either configuration depending on its connectivity. Important trick is wait_for_monitor function. I found that X server (or xrandr) sometimes significantly lags behind udev/kernel event. This function ensures xrandr actually sees externel monitor connected.

Another cool thing here is i3plug.py. Initially I found this script somewhere on the web and slightly modified it to my needs. It saves current i3 layout and can restore it some time later. Obviously, it saves the layout on monitor unplug (undocking) and restores when laptop again finds its place on the docking station.

#!/usr/bin/env python
import os
import i3
import sys
import pickle


PATH = "/home/USERNAME/.i3/workspace_mapping"


def showHelp():
    print(sys.argv[0] + " [save|restore]")


if __name__ == '__main__':
    if len(sys.argv) < 2:
        showHelp()
        sys.exit(1)

    if sys.argv[1] == 'save':
        pickle.dump(i3.get_workspaces(), open(PATH, "wb"))
    elif sys.argv[1] == 'restore':
        try:
            workspace_mapping = pickle.load(open(PATH, "rb"))
        except Exception:
            print("Can't find existing mappings...")
            sys.exit(1)

        for workspace in workspace_mapping:
            i3.msg('command', 'workspace %s' % workspace['name'])
            i3.msg('command', 'move workspace to output %s' % workspace['output'])
        for workspace in filter(lambda w: w['visible'], workspace_mapping):
            i3.msg('command', 'workspace %s' % workspace['name'])
    else:
        showHelp()
        sys.exit(1)

Wired and wireless internet switch

Another useful addition is to use wired connection (with RJ45 cable attached to dock station) when using dock and WiFi without it. This is achieved with a help of netctl failover profile. Archwiki article perfectly explains how to do that.

In short, install ifenslave package and enable bonding:

$ cat /etc/modules-load.d/bonding.conf
bonding

$ cat /etc/modprobe.d/bonding.conf
options bonding mode=active-backup miimon=100 primary=eth0 max_bonds=0

Create failover netctl profile (cat /etc/netctl/failover), tune wired and wireless interfaces names:

Description='A wired connection with failover to wireless'
Interface='bond0'
Connection=bond
BindsToInterfaces=('enp0s25' 'wlp3s0')
IP='dhcp'

Create wpa_supplicant service:

$ cat /etc/wpa_supplicant/wpa_supplicant-wlan0.conf
ctrl_interface=/run/wpa_supplicant
update_config=1

network={
    ssid="SSID"
    psk=PSK
}

Finally, enable netctl and wpa_supplicant@ template service. That’s it.