I've been managing network connections on my laptop by hand, and I was just thinking that I'd like it to bring up its NICs automatically if it's plugged in, but I didn't want to use ifplugd for various reasons, and anyway, I like ifupdown and I want to stick with it.
I found Debian bug #120382 and it suggested using mii-tool in pre-up, and
that was just the right thing to do. The suggestion in the bug wasn't quite
the right syntax, but the right syntax was pretty obvious given the general
idea:
---------------------------------------------------------------------------
auto eth0
iface eth0 inet dhcp
pre-up /sbin/mii-tool eth0 | /bin/grep -qv "no link"
auto wlan0
iface wlan0 inet dhcp
pre-up /sbin/mii-tool eth0 | /bin/grep -q "no link"
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
---------------------------------------------------------------------------
The effect of this is that if I'm plugged into a wired network, eth0 fires
up dhclient. If I'm not, wpa_supplicant does its thing.
Interesting reading:
/usr/share/doc/ifupdown/examples/network-interfaces
There are a bunch of fun things you can do with ifupdown without invoking
the complexity of Network Manager documented there, but this mii-tool trick
isn't mentioned.
For folks on laptops, something worth learning is how to use
wpa_supplicant.conf to try a range of networks automatically. You can then
progressively try, for example, your home network, a work network, a coffee
shop network, and then look for open networks:
/usr/share/doc/wpasupplicant/README.Debian.gz
/usr/share/doc/wpasupplicant/examples/wpa_supplicant.conf
...and all only if the wired network isn't plugged in, if you use the
mii-tool trick.
Example /etc/wpa_supplicant/wpa_supplicant.conf:
---------------------------------------------------------------------------
network={
ssid="My Home"
psk="super secret"
priority=20
}
network={
ssid="Coffee Shop"
psk="also super secret"
priority=15
}
# But you're better off buying Fair Trade and drinking it at home.
# Work:
network={
ssid="MegaCorpWifi"
key_mgmt=WPA-EAP
eap=TTLS
identity="u...@example.com"
anonymous_identity="anonym...@example.com"
password="foobar"
ca_cert="blob://exampleblob"
priority=10
}
# Try open networks if none of the above are answering.
network={
key_mgmt=NONE
}
---------------------------------------------------------------------------
I'm mostly writing this so people realize that they aren't forced to use
some convoluted tool to flexibly manage networking. You can cover a wide
range of situations with good old ifupdown.
--
Mason Loring Bliss ma...@blisses.org Ewige Blumenkraft!
awake ? sleep : random() & 2 ? dream : sleep; -- Hamlet, Act III, Scene I
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