Yrurtj

With Network Manager in Red Hat 7, I am seeing an issue where the old/wrong search domain is being used after changing the hostname. In /etc/resolv.conf, I see:

# Generated by NetworkManager

search **ec2.internal** d.sample.com

nameserver 172.31.0.2

When I type hostname, I see my desired output:

[root@testing01 ~]# hostname

testing01.d.sample.com

But instead of replacing the search domains, it is appending the new domain name to the search domains. I want to completely get rid of ec2.internal and give this domain the ax altogether. Editing the /etc/resolv.conf file directly gets clobbered by Network Manager. I don't want to disable Network Manager, and I'd rather not disable NM's management of /etc/resolv.conf unless I absolutely have to.

So, 1) Why does NM keep reverting my search domain and 2) how can I fix this using nmcli or command line tools only?

The /etc/resolv.conf file will always be overwritten when there is a change or update to the network. You can control what is written by editing files in the /etc/resolvconf/resolv.conf.d/ folder... namely the head file.

Place this in the /etc/resolvconf/resolv.conf.d/head file:

nameserver 172.31.0.2

search testing01.d.sample.com

Now this will be the header of the /etc/resolv.conf each time it's updated.

Update

For Redhat based systems, use these steps:

Edit your network script which is located at: /etc/sysconfig/network-scripts. You will see an entry for the network devices detected (i.e. ifcfg-eth0 for the network adapter eth0).

Edit this file (/etc/sysconfig/network-scripts/ifcfg-eth0):

Append this line:

DOMAIN=sample.com

Also run this command:

$ sudo hostnamectl set-hostname --static "testing01.d.sample.com"

You'll most likely have to reboot the system to make the changes take effect.

After a few hours of poking around, I was able to resolve this. It turns out, this was being set via DHCP:

nmcli -f ip4 device show eth0

IP4.ADDRESS[1]:                         172.31.53.162/20

IP4.GATEWAY:                            172.31.48.1

IP4.DNS[1]:                             172.31.0.2

IP4.DOMAIN[1]:                          ec2.internal

I was able to override IP4.DOMAIN[1] by overriding a network interface's ipv4.dns-search value:

nmcli connection modify uuid `nmcli connection show --active | grep 802-3-ethernet | awk '{print $(NF-2)}' | tail -n 1` ipv4.dns-search d.sample.com

Or more simply,

nmcli connection modify System eth0 ipv4.dns-search "d.sample.com"

Then you have to restart NetworkManager

systemctl restart NetworkManager.service

I also found that because I was working with an Amazon instance, I needed to update my cloud.cfg file.

If "nmcli connection modify ..." has changed your connection file but not your active connection:

nmcli c load /etc/NetworkManager/system-connections/the-connection-name[-possibly-uuid-too]

man nmcli:
connection--
load filename...
Load/reload one or more connection files from disk. Use this after manually editing a connection file to ensure that NetworkManager is aware of its latest state.