how does /etc/network/interfaces actually work? information maybe missing in man page

blueSn0w · 08-19-2014, 12:16 PM

Hi LQ users, this is my first post here so if i am posting this in a wrong way please tell me

.

To the problem.
I was trying to learn how to connect to a wpa2 secured network without the GUI network manager. So i followed a tutorial (sadly i do not remember where it was) and it told me how to configure the /etc/wpa_supplicant.conf and /etc/network/interfaces files in order to connect to wifi.

according to interfaces man page there are no options to write in the "iface wathever manual" stanza. But i have two lines there defining that (i supose) wpa_supplicant will use.

My question is: As interfaces manpage does not show these options, where do i find how it works, what program is actually reading this file (i suposed ifup, but ifup:s manpage does not explain how these options are used either.)
Is it ifup that starts up the interface at startup and sends the options to wpa_suplicant?

This is my interface file:

Code:

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

auto eth1
iface eth1 inet manual
        wpa-driver nl80211  <- this line is explained nowere
        wpa-roam /etc/wpa_supplicant.conf <- or this

iface hallo inet dhcp

... and this is my wpa_supplicant.conf file:

Code:

ctrl_interface=/var/run/wpa_supplicant
ctrl_interface_group=netdev
update_config=1

network={
        ssid="hallo"
        #psk="mypassword"
        psk=somecode i suppose is secret
        id_str="hallo"
}

I supose i could have found how this works somewhere. But i searched and didnt really find how it works. Is there any "official" page that does actually explain how these commands work?

If it is important: my distro is linux mint KDE and i dont have any gui network manager running

rtmistler · 08-19-2014, 12:30 PM

Welcome to LQ!

I've not done this with /etc/network/interfaces but instead written a script and left any semblence of my wireless device out of the interfaces file.

The gist of my script:

Code:

# $ESSID and $PSK were passing arguments to my script
# ESSID is the SSID of the WIFI
# PSK is the shared secret for WPA
# $IFACE is my wireless interface which is typically wpa0 for my case

/sbin/start-stop-daemon -K -x /sbin/wpa_supplicant;
/usr/bin/wpa_passphrase $ESSID $PSK > $HOME/wpa.conf;
/sbin/wpa_supplicant -B -Dwext -i$IFACE -c$HOME/wpa.conf;

# Then beyond this I'd either have a static IP
# or I'd obtain one via dhclient
# Static IP:

ifconfig $IFACE $IP_ADDR
route add default gw $GATEWAY

# DHCP:

dhclient $IFACE

How I got there was web searching and trial/error with my system until I got a reliable way to get it working. So perhaps things are different on your system, but here's hoping that some of these suggestions help.

ondoho · 08-19-2014, 01:17 PM

it pays to look at the age of the tutorials one is following, and if they're suitable for or targeted at your distro.

also, if you want to go the (semi-)manual way, you might have to actually uninstall or at least thoroughly disable networkmanager, which digs its greedy claws deep into your system.

blueSn0w · 08-19-2014, 01:42 PM

Thank you very much for your quick responses!

I am really sorry that i didnt specify that my setup was actually working quite well for me.
And yes i did remove the networkmanager that was installed before.
Thank you rtmistler for your script! I think i will try to understand it and then use it, as i wasn't really understanding what was going on in the background with my previous setup.

PS. why have you used ; signs at the end of the first lines in your script?

rtmistler · 08-19-2014, 01:54 PM

Quote:

Originally Posted by blueSn0w

PS. why have you used ; signs at the end of the first lines in your script?

That's mainly due to my scripting style. The semicolon means that this is the end of a command, and hence someone could write a script line as:

Code:

ls;ls -a;

Placing it all on the same physical line. I tend to still use the semicolon at the end of commands; however you can avoid that if your commands are all on separate lines.