How to set static DNS with dhclient while resolv.conf keeps getting overwritten?

Question

Following the Debian NetworkConfiguration wiki, I've been trying to setup static OpenNIC DNS with no success. The first thing I tried was directly editing /etc/resolv.conf, but it keeps getting overwritten. The wiki page lists three possible sources of the overwrite:

1. The resolvconf program
2. The network-manager daemon
3. DHCP clients

$ apt-cache policy resolvconf
resolvconf:
  Installed: (none)
  Candidate: 1.76.1
  Version table:
     1.76.1 0
        500 http://ftp.us.debian.org/debian/ jessie/main amd64 Packages
$ apt-cache policy network-manager
network-manager:
  Installed: (none)
  Candidate: 0.9.10.0-7
  Version table:
     0.9.10.0-7 0
        500 http://ftp.us.debian.org/debian/ jessie/main amd64 Packages

Considering I don't have resolvconf or network-manager installed, we can assume the source is a DHCP client. I'm using wicd as an alternative to network-manager, but setting up static dns in the wicd-gtk properties doesn't work. Thus, I edited /etc/dhcp/dhclient.conf by adding supersede domain-name-servers 50.116.40.226;, but my /etc/resolv.conf is still:

$ cat /etc/resolv.conf
nameserver 2001:558:feed::2
nameserver 2001:558:feed::1

What is the hell is going on here? Should I install resolvconf to see if it will work? Should I give up on wicd and install network-manager?

Solution 1

Use the following workaround to prevent the dhcp client from updating your carefully crafted /etc/resolv.conf:

# chattr +i /etc/resolv.conf

Solution 2

I think that your DHCP server sends unsolicited responses, so your resolv.conf was overwritten also if you set the supersede parameter. Adding the +i attr may be a solution but requires that you manually unset and re set it if you have to do some changes.

You can, indeed, write some scripts on the client side (see man 8 dhclient-script).

This topic is also explained in debian wiki:

Another approach makes use of dhclient-script's hook scripts. According to dhclient-script(8):

When it starts, the client script first defines a shell function, make_resolv_conf , which is later used to create the /etc/resolv.conf file. To override the default behaviour, redefine this function in the enter hook script. Therefore, we can stop dhclient from overwriting resolv.conf by doing the following:

echo 'make_resolv_conf() { :; }' > /etc/dhcp/dhclient-enter-hooks.d/leave_my_resolv_conf_alone
chmod 755 /etc/dhcp/dhclient-enter-hooks.d/leave_my_resolv_conf_alone

The execute bit is required because dhclient-script uses run-parts(8) to decide which files to read. For that same reason, the filename must not contain anything but letters, digits, underscores and hyphens.

Comments

[ctrl-d]

It's probably a bug in dhclient, which i also ran into. It ignores the supersede. I ended up making /etc/resolv.conf immutable with chattr. But i'm interested in a permanent solution too.

[lscstu22]

@ctrl-d Bravo, sudo sh -c 'printf "name server 169.57.14.220\nnameserver 190.10.8.128\n" > /etc/resolv.conf' && sudo chattr +i /etc/resolv.conf works! Post an answer along the same lines, and I'll accept it

[ctrl-d]

You're welcome. Good that it works for you too.

[lscstu22]

@roaima sorry for the late reply, but no it wasn't: -rw-r--r-- 1 root root 49 Dec 14 18:19 resolv.conf

[Patrick Mevzek]

What version of Debian do you use? If this is a recent one, you have systemd on it, and it overwrites /etc/resolv.conf on networl changes.

[lscstu22]

I'd like to add I had to combine the editing and chattr commands into one with && for this to work since /etc/resolv.conf was being overwritten so quickly. Check out the question comments above.

[ctrl-d]

I just put in: nameserver 127.0.0.1 and chattr-ed it.