How to Configure Networking on Ubuntu

Configure network using init networking (text mode)

    /etc/network/interfaces

12.04 or later

    $ sudo /etc/init.d/networking restart

Normally dns-* option in /etc/resolv.conf can be configured in /etc/network/interfaces. Don’t need to specify it in /etc/resolvconf/resolv.conf.d

    dns-search
    dns-nameserver
    dns-nameservers

/etc/resolv.conf is an symlink to /run/resolvconf/resolv.conf or /etc/resolvconf/run/resolv.conf

note: in resolv.conf, do use “search” instead of “domain” option because the search feature supersedes the domain feature. Unlike domain, search accepts multiple arguments.

Once configured in /etc/network/interfaces, use resolvconf tool

    $ man resolvconf
    $ resolvconf -u

If /etc/resolv.conf doesn’t look right, maybe the resolvconf interface database needs to be updated by -d (delete) and -a (add) arguments

    $ resolvconf -d eth0
    $ ls /etc/resolvconf/run/interface       # you shouldn't see eth0 file
    $ resolvconf -a eth0
    $ ls /etc/resolvconf/run/interface       # now you should see the file and its content matched yours

In otherwords, to update the database you have to call resolvconf with the -a or -d option. That happens behind the scenes when you run ifup or ifdown. So, normally, as with any other change to /etc/network/interfaces, to activate changes to the dns-* options you have to ifdown the interface in question and ifup it again. Or you can reboot.

referrence

If you don’t want resolv.conf to take effect, make /etc/resolv.conf a regular file

check if resolvconf install

    $ dpkg --list | grep resolv

if not installed

    $ sudo apt-get install resolvconf

add config in /etc/resolvconf/resolv.conf.d/head

agian, /etc/resolv.conf is an symlink to /run/resolvconf/resolv.conf or /etc/resolvconf/run/resolv.conf

Configure network using network manager gui (graphic mode)

restart all interface

    $ sudo service network-manager restart

restart specific interface

    $ sudo service network-interface restart INTERFACE=eth0

Caveat

There is a bug that if 2 network interfaces configured on network manager gui and/or /etc/network/interfaces, there will be confusion. Suggestion is to configure on /etc/network/interfaces on both interfaces.

error message looks similar to this

    syslog.1:Oct  6 12:32:26 myhost NetworkManager[763]: <info> Unmanaged Device found; state CONNECTED forced. (see http://bugs.launchpad.net/bugs/191889)
    syslog.1:Oct  6 12:32:26 myhost NetworkManager[763]: <info> Activation (eth0) Beginning DHCPv4 transaction (timeout in 45 seconds)
    syslog.1:Oct  6 12:32:26 myhost NetworkManager[763]: <info> dhclient started with pid 14990
    syslog.1:Oct  6 12:32:26 myhost NetworkManager[763]: <info> Activation (eth0) Beginning IP6 addrconf.
    syslog.1:Oct  6 12:32:26 myhost NetworkManager[763]: <info> Activation (eth0) Stage 3 of 5 (IP Configure Start) complete.
    syslog.1:Oct  6 12:32:26 myhost NetworkManager[763]: <info> (eth0): DHCPv4 state changed nbi -> preinit
    syslog.1:Oct  6 12:32:46 myhost NetworkManager[763]: <info> (eth0): IP6 addrconf timed out or failed.
    syslog.1:Oct  6 12:32:46 myhost NetworkManager[763]: <info> Activation (eth0) Stage 4 of 5 (IP6 Configure Timeout) scheduled...
    syslog.1:Oct  6 12:32:46 myhost NetworkManager[763]: <info> Activation (eth0) Stage 4 of 5 (IP6 Configure Timeout) started...
    syslog.1:Oct  6 12:32:46 myhost NetworkManager[763]: <info> Activation (eth0) Stage 5 of 5 (IP Configure Commit) started...
    syslog.1:Oct  6 12:32:46 myhost NetworkManager[763]: <info> Activation (eth0) Stage 5 of 5 (IP Configure Commit) failed (no IP configuration found)

link to bug