MINT > résoudre l’écrasement des DNS lors du reboot

UPDATE2 AND SOLUTION:I commented the part out (#Start to #End), that seemingly overwrites the /etc/resolv.conf file and sure enough. That was the culprit. So an obscure script caused all this trouble.

I changed the question to reflect, what actually needed to be known to solve my problem, so it would be easier to find for people with the same problem and so I could accept an answer.

Thanks for the help here in figuring things out.

 

Setting the immutable flag on resolv.conf doesn’t work as you expected as the file was not changed. The directory entry in /etc was changed when the file was renamed. You’d have to set /etc to be immutable - something you really don’t want to do.

@DougO’Neal I see. Thanks for the heads up.

8 Answers

1) You shouldn’t manually update your resolv.conf, because all changes will be overwritten by data that your local DHCP server provides. If you want it to be static, run sudo dpkg-reconfigure resolvconf and answer "no" to dynamic updates. If you want to add new entries there, edit /etc/resolvconf/resolv.conf.d/base and run sudo resolvconf -u, it will append your entries and DHCP server’s entries.

2) Try to edit your /etc/network/interfaces and add your entries there, like

auto eth0
iface eth0 inet dhcp
dns-search google.com
dns-nameservers dnsserverip

and then restart /etc/init.d/networking restart or sudo ifdown -a and sudo ifup -a

3) Your system uses udhcp which is a very small DHCP client program. The udhcp client negotiates a lease with the DHCP server and notifies a set of scripts when a leases is obtained or lost. You can read about it’s usage here or just edit this script (as you did).

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• 1I did add the entries into the /etc/resolvconf/resolv.conf.d/base and ran resolvconf -u. It didn’t work, unfortunately.
• Have you tried to run sudo dpkg-reconfigure resolvconf? After running resolvconf -u, your entries wasn’t in result file? How did you add them, like "nameserver 127.0.0.1″ or "search google.com"?
• I did run dpkg-reconfigure resolvconf. The entries were not in there. And I have entries with both nameserver ip and search domain.
• No, running dpkg-reconfigure resolvconf won’t add entries, but you can disable automatic updates. If you disable updates, you can edit resolv.conf manually and it shouldn’t be overwritten.
• My bad for phrasing it so clumsily, I was answering your comment sentence by sentence. After running resolvconf -u the entries were not added.

I ran into this too. Commenting out domain-name-server didn’t fix it for me either.

Also, I’m not using resolvconf, just plain /etc/resolv.conf.

I didn’t try using chattr +i to lock down resolv.conf because it seems too hacky. Also, I want Puppet to be able to modify resolv.conf when necessary.

The best solution I found overrides the default behavior of dhclient using its documented hooks.

Create a new file at /etc/dhcp/dhclient-enter-hooks.d/nodnsupdate with the following contents:

#!/bin/sh
make_resolv_conf() {
    :
}

Then make the file executable:

chmod +x /etc/dhcp/dhclient-enter-hooks.d/nodnsupdate

Now when dhclient runs -- either on reboot or when you manually run sudo ifdown -a ; sudo ifup -a -- it loads this script nodnsupdate. This script overrides an internal function called make_resolv_conf() that would normally overwrite resolv.conf and instead does nothing.

This worked for me on Ubuntu 12.04.

• Didn’t work on Ubuntu 18.04 :( /etc/resolv.conf was overwritten after reboot. – Dan Dascalescu Oct 21 at 4:50

Ubuntu 16.04 If the network interfaces for your server instance is controlled by DHCP, the dhclient program will overwrite your /etc/resolv.conf file whenever the networking service is restarted.

You can fix the issue by editing the /etc/dhcp/dhclient.conf file and adding “supersede” statements for domain-name, domain-search and domain-name-servers as follows:

supersede domain-name "local.com";
supersede domain-search "local.com";
supersede domain-name-servers 192.168.56.103;

In this particular case the name server is located at "192.168.56.103″ and the domain name is "local.com"

Note that each line is terminated by a semi-colon and the domain name is enclosed in double quotes.

• Unfortunately this didn’t work on Ubuntu 18.04. After rebooting, /etc/resolv.conf was overwritten with 127.0.0.53. – Dan Dascalescu Oct 21 at 4:52
• May be you can try this askubuntu.com/questions/1031279/… – Sand1512 Oct 21 at 10:21
• Also check if you are running dnsmasq – Sand1512 Oct 21 at 10:22

go to this directory:

  cd /etc/resolvconf/resolv.conf.d

Open the file named head and put the DNS IPs or names in there. Open the file named tail and put the domain in there. Reboot.

• That directory doesn’t exist by default on Ubuntu 18.04. Do you need to install a service that creates it? – Dan Dascalescu Oct 21 at 4:55

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0

In Azure VMs /etc/resolv.conf is not directly editable.

Try adding the DNS entiries in your network configuration files /etc/sysconfig/network-scripts/ifcfg-eth0 and so on like below:

DOMAIN=example.com

DNS1=10...*
DNS2=10...*
DNS3=10...*

and restart the network service after saving the files. you will see the configuration will then be added into the resolve.conf as well.

 

To make the DNS related changes in resolv.conf permanent, you need to change the DHCP configuration file named dhclient.conf. You can find the file in /etc/dhcp/dhclient.conf.

Open the file for editing (don’t forget to use sudo). You’ll see lines like these:

#supersede domain-name "fugue.com home.vix.com";
#prepend domain-name-servers 127.0.0.1;

Remove the preceding “#” and use the domain-name and/or domain-name-servers which you want. Save it. Now the DNS related changes will be permanent.

Credits goes to: https://itsfoss.com/resolvconf-permanent-ubuntu/

 

Use the below command to prevent the resolv.conf or any file from overwriting after reboot

chattr -V +i filename e.g chattr -V +i /etc/resolv.conf

To Revert Back the Change Use the below Command :

chattr -i filename - to re-enable insert to the file

chattr (Change Attribute) is a command line Linux utility that is used to set/unset certain attributes to a file in Linux system to secure accidental deletion or modification of important files and folders, even though you are logged in as a root user.

• I believe that the user in the question actually tried chattr, but obverved that this had no effect. – Kusalananda♦ Oct 15 at 21:25
• This will work for sure , The option user tried is for editing the file not for making it immutable – Ashish Jain Oct 16 at 13:09
• Please run the command with sudo chattr -V +i filename e.g sudo chattr -V +i /etc/resolv.conf – Ashish Jain Oct 16 at 13:16

On ubuntu 18.04 using NetworkManager. You need to remove the ‘resolv.conf’ file and let NetworkManager generate one for you.

To remove the file in terminal type sudo rm -f /etc/resolv.conf; this will delete the file for you.

Reboot the system and NetworkManager will generate a resolv.conf file for you.