Start by downloading the latest ev3dev release from http://www.ev3dev.org/download/.
Once downloaded, set it up as a loop device. Find out what the first unused loop device is by running losetup -f.
This tells you which loop device will be used once set up. On my system, it printed /dev/loop0. Now we can run
the command to actually set up the loop device:
sudo losetup -Pf /path/to/ev3dev.img
This will have created a few device endpoints in /dev: /dev/loop0, /dev/loop0p1, and /dev/loop0p2.
These are the loop device and its two partitions. We're interested in the second partition, and will mount
it with the default settings (both read and write) at /mnt.
sudo mount /dev/loop0p2 /mnt
As root, open /mnt/etc/fstab in a text editor and edit it as shown below. Change the options for /boot/flash and /
to include the read-only flag ro. At the end of the file, add a new virtual file system for /tmp so that temporary
files can still be created. Because the EV3 is short on RAM, we're only using 20M of it for this purpose.
#<file system> <mount point> <type> <options> <dump> <pass>
/dev/mmcblk0p1 /boot/flash vfat defaults,errors=remount-ro,noatime,ro 0 2
/dev/mmcblk0p2 / ext4 defaults,errors=remount-ro,noatime,ro 0 1
proc /proc proc defaults 0 0
tmpfs /tmp tmpfs defaults,size=20M 0 0
Start by disabling connman, as we will not be using it.
sudo ln -s /dev/null /mnt/etc/systemd/system/connman.service
As root, create /mnt/etc/network/interfaces with -rw-r--r- permissions and write to it as shown below.
# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d
auto lo
iface lo inet loopback
# Automatically configure WiFi
auto wlan0
# Allow the wifi device to be removed and reinserted
allow-hotplug wlan0
# Get a network address from DHCP
iface wlan0 inet dhcp
# Load WiFi configuration from this file
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
Create /mnt/etc/wpa_supplicant/wpa_supplicant.conf with -rw------ permissions and write to it as shown below.
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=ev3dev
update_config=1
network={
ssid="YourSSID"
psk="YourPre-SharedKey"
}
You will not be able to run systemctl enable service normally because everything is read-only, so you'll have to create
the required symlinks by hand. For a normal service that is WantedBy=multi-user.target, this entails creating a symlink
to your service in /etc/systemd/system/multi-user.target.wants/. For example:
sudo ln -s /etc/systemd/system/mycustom.service /etc/systemd/system/multi-user.target.wants/mycustom.service
Once you have made your changes to the ev3dev image, you should properly unmount it. Start by running umount on
your mount point /mnt:
sudo umount /mnt
Once unmounted, detach the original loop device. Make sure to use the correct loop device so you don't detach the wrong thing by accident.
sudo losetup -d /dev/loop0