debian - connect to wifi automatically when in range

Question

I have a LeMaker Guitar with Lemuntu installed. My wpa_supplicant.conf file looks like this:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
   ssid="MySSID"
   psk="MyPasswd"
}

and my /etc/network/interfaces file looks like this:

auto wlan0
iface wlan0 inet dhcp
pre-up wpa_supplicant -B -i wlan0 -c/etc/wpa_supplicant/wpa_supplicant.conf
pre-down killall -q wpa_supplicant

When I boot up my Guitar and the wi-fi router is already running the wi-fi connects just fine. But when I boot up my Guitar and power up router after, it does not connect. I tried to create cron job that every minute does dhclient wlan0 but it didn't work.

So my question is, how to connect automatically to this wi-fi if it goes up after I booted the Guitar.

Answer 1

Solution: Network-Manager without GUI.

I tried half a dozen tutorials using wpa-supplicant, iw and /etc/network/interfaces. But they all did not work for me. Probably because they did not describe at all what they were doing. So I always ran into a point where it did not work and there was no error message nor any way to find out the source of the problem.

Finally I simply tried installing the default network-manager. Which happens to be the gnome-network-manager but without the GUI components (-> --no-install-recommends).

So in short, the solution is:

sudo apt install --no-install-recommends network-manager
nmcli connection add ifname wlan0 type wifi ssid MySSID
nmcli connection edit wifi-wlan0

While editing the config file you have to set WPA-PSK and the plain text password:

nmcli> goto wifi
nmcli 802-11-wireless> set mode infrastructure 
nmcli 802-11-wireless> back 
nmcli> goto wifi-sec 
nmcli 802-11-wireless-security> set key-mgmt wpa-psk 
nmcli 802-11-wireless-security> set psk your-plain-text-password
nmcli 802-11-wireless-security> save 
nmcli 802-11-wireless-security> quit 

After that reboot and enjoy! The network-manager will take care of everything!

If it complains about permission, the recommended way seems to be to modify/overwrite the policykit rules from /usr/share/polkit-1/actions/org.freedesktop.NetworkManager.policy. I gave up on that and used sudo instead. If anybody knows a clean way to do it, tell us please!

Here is a very good guide, but it's in german: https://wiki.ubuntuusers.de/NetworkManager/NetworkManager_ohne_GUI/

Answer 2

This is a sample script to check the wlan0 stat , connecting and getting an IP address through dhcp:

/bin/ip link set wlan0 up
if grep -q 0 /sys/class/net/wlan0/carrier
then
killall wpa_supplicant
/sbin/wpa_supplicant -B -i wlan0 -c/etc/wpa_supplicant/wpa_supplicant.conf  > /dev/null 2>&1
/sbin/dhclient -r
/sbin/dhclient  > /dev/null 2>&1
fi

A cron job to run this script every minute.

* * * * * /path/to/script.sh

Edit : you can use ping to test the connectivity.

/bin/ping -q -c3 8.8.8.8  > /dev/null
if [ $? -ne 0 ]
then
killall wpa_supplicant
/bin/ip link set wlan0 up
/sbin/wpa_supplicant -B -i wlan0 -c/etc/wpa_supplicant/wpa_supplicant.conf  > /dev/null 2>&1
/sbin/dhclient -r
/sbin/dhclient  > /dev/null 2>&1
fi