Putting a network interface up/down from command line

  • 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?

  • sgargel

    sgargel Correct answer

    5 years ago

    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

    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.

    If using *WPA* take also a look to `wpasupplicant`. A search to "ubuntu WPA wifi command line" will give you many links like: http://ubuntuforums.org/showthread.php?t=1798927 http://askubuntu.com/questions/461825/connect-to-wifi-from-command-line

    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.

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Content dated before 6/26/2020 9:53 AM