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In Xubuntu 14.04, I tried to use both ip and ifconfig to handle a network interface, but they gave the same result.

$ sudo ifconfig wlan0 down
$ sudo ip link set wlan0 down

both correcly put down the interface and the connectivity does not work; but then

$ sudo ifconfig wlan0 up
$ sudo ip link set wlan up

did not restore the connectivity!

This is the output of ip link show after putting the interface down:

wlan0: <BROADCAST,MULTICAST> mtu 1500 qdisc mq state DOWN group default qlen 1000
link/ether <my_MAC_address> brd ff:ff:ff:ff:ff:ff
inet 192.168.1.29/24 brd 192.168.1.255 scope global wlan0
   valid_lft forever preferred_lft forever

and this is the output after putting the interface up:

wlan0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
link/ether <my_MAC_address> brd ff:ff:ff:ff:ff:ff
inet 192.168.1.29/24 brd 192.168.1.255 scope global wlan0
   valid_lft forever preferred_lft forever

So it has no carrier and I can't access the web, but it has an IP!

1) Why? Shouldn't the up command restore the previous situation? I had to turn off and on the physical switch of the wireless board to browse again the web. I also tried with dhclient -r wlan0 and dhclient wlan0, but the result was that neither the physical switch was useful and I had to restart the whole system.

2) Even after putting the interface down, the GUI connectivity icon was active and a connection to the wireless Access-Point was normally shown (even if no webpages were actually available). Why?

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2 Answers 2

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12

I think that ifconfig is not handling wireless stuff like ESSID, channel and key. Take a look to iwconfig instead.

http://manpages.ubuntu.com/manpages/vivid/en/man8/iwconfig.8.html

-EDIT-

You can also use "NetworkManager command line" nmcli: https://askubuntu.com/questions/461825/connect-to-wifi-from-command-line

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  • 1
    thanks, but can you provide some example about deactivating and reactivating the wireless card? After reading the original manual (the one you provided is in Italian!) I did not find such an example.
    – BowPark
    Commented Feb 17, 2016 at 15:42
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    If using WPA take also a look to wpasupplicant. A search to "ubuntu WPA wifi command line" will give you many links like: ubuntuforums.org/showthread.php?t=1798927 askubuntu.com/questions/461825/…
    – sgargel
    Commented Feb 18, 2016 at 9:50
  • with the second link I succeded to correctly shut down and then put up the interface. Maybe you can include it in your answer, and I will choose it.
    – BowPark
    Commented Feb 18, 2016 at 22:56
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1) This answer is only for a wired connection. Use ifup and ifdown, not ifconfig, unless you want to manually specify the parameters. ifup will look at your network configuration in /etc/network/interfaces (or wherever your distro puts it).

2) If you're using wpa for your wifi, you cannot connect to it with just ifup; a helper application must be configured and running (usually wpa_supplicant). Usually your distro will provide you with network scripts to perform these tasks automatically.

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  • Ok, yes I use WPA very often. So a configuration is needed to be set up when the interface turns up again, which makes the re-connection a non-trivial task?
    – BowPark
    Commented Feb 17, 2016 at 18:46

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