If I add a new DNS server using nmcli connection modify eth0 +ipv4.dns 8.8.8.8, I still have to update /etc/resolv.conf for the resolver to pick up the changes, right? So how do I force the update?
The only way I found was restarting the network service: /etc/init.d/network restart. Is there a less invasive way -- a nmcli command, perhaps?
based on http://www.certdepot.net/rhel7-configure-ipv4-addresses/
nmcli connection up eth0
run after mod calls, worked for me.
P.S. you can use "nmcli -p connection show eth0" to see the configured vs active settings
If nmcli is NOT available (for example when NetworkManager is not installed) there is another way (handy on older Linux 6 distros) to add and remove new settings at will from /etc/resolv.conf without restarting network and without manually editing /etc/resolv.conf file. The steps are:
Create a virtual NIC following the steps as described here or any other reference on creating a virtual NIC (e.g. ifcfg-eth0:0).
Note: I also change BOOTPROTO=none and NM_CONTROLLED=no in the ifcfg-eth0:0 file.
DNS1="8.8.8.8 7.7.7.7"
DOMAIN="urdomain1.com urdomain2.com"
sudo ifup ifcfg-eth0:0
The new settings can be "switched off" (removed) by running:
sudo ifdown ifcfg-eth0:0
and this method should work on any distro whether it has nmcli or not. This is arguably a variation on Giomac's answer, but it has the additional advantage that this VNIC can be brought up and down without affecting anything except that it will update the /etc/resolv.conf in both (up and down) directions.
Add following to interface configuration file (/etc/sysconfig/network-scripts/ifcfg-ethX):
PEERDNS=yes
DNS1=1.2.3.4
DNS2=1.2.3.4
NM_CONTROLLED=yes
bring interface up:
ifup ethX
To do so, you will need to identify your network interface (i.e eth0)
# nmcli conn
NAME UUID TYPE DEVICE
eth0 74315f7c-1573-4150-9c0e-e06ad28cac95 802-3-ethernet eth0
#
# nmcli conn edit eth0
===| nmcli interactive connection editor |===
Editing existing '802-3-ethernet' connection: 'eth0'
Type 'help' or '?' for available commands.
Type 'describe [<setting>.<prop>]' for detailed property description.
You may edit the following settings: connection, 802-3-ethernet (ethernet), 802-1x, ipv4, ipv6, dcb
nmcli> print ipv4.dns-search
ipv4.dns-search: mydomain.linux.com
nmcli>
nmcli> set ipv4.dns-search mylinuxdomain.com,anotherdomain.com
nmcli>
nmcli> save permanent
Then restart your network. I use nmcli to do so: 1. To bring down
# nmcli conn down eth0
2. To bring up
# nmcli conn up eth0
Show available device to configure: nmcli c s
You will need the NAME or the UUID of that list. Let's assume the connection name is eth0.
Show the current IPv4 DNS settings of eth0: nmcli c s eth0 | grep ipv4.dns:
sudo nmcli c m eth0 ipv4.dns "8.8.8.8 8.8.4.4"sudo nmcli c up eth0Bonus:
ssh remote-server 'sudo nmcli c m eth0 ipv4.dns "8.8.8.8 8.8.4.4" && sudo nmcli c up eth0'
Searched quite some time for the correct answer, and found it in another stack overflow post (source). This annoying thing is a known systemd bug, so you need to recreate the symlink pointing to the correct file.
sudo rm -f /etc/resolv.conf
sudo ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf
reboot
Before you do this, check if the file contains the correct DNS entries:
sudo cat /run/systemd/resolve/resolv.conf
How to set DNS in CentOS/RHEL 7 & prevent NetworkManager from overwriting /etc/resolv.conf?
Source : [enter link description here][1]
The NetworkManager configuration is located here: /etc/NetworkManager/NetworkManager.conf Open this file using vim or your favorite text editor.
Search for the [main] section in this file. It should look something like this:
... [main] #plugins=ifcfg-rh,ibft ... Add dns=none just after the [main] tag like this:
...
[main]
dns=none
#plugins=ifcfg-rh,ibft
...
Go ahead and save the file.
Let’s restart the NetworkManager.service service so that it picks up the changes we made to the configuration.
sudo systemctl restart NetworkManager.service Note that the service name NetworkManager.service is case-sensitive.
Now, let’s add our nameservers to /etc/resolv.conf
Open this file in you favorite text editor and specify the name servers as follows:
# Generated by NetworkManager
nameserver 8.8.8.8
nameserver 8.8.4.4
CentOS / RHEL : DNS servers in /etc/resolv.conf change after a reboot/network service restart. How to make them permanent
Source : [https://www.thegeekdiary.com/centos-rhel-dns-servers-in-etcresolv-conf-change-after-a-rebootnetwork-service-restart-how-to-make-them-permanent/][2]
You would face this issue after a reboot or a network service restart. This usually happens as the scripts /etc/sysconfig/network-scripts/ifup-post and /etc/sysconfig/network-scripts/ifdown-post checks for the parameters “RESOLV_MODS=no” or “PEERDNS=no” in the network interface configuration file such as /etc/sysconfig/network-scripts/ifcfg-*. If these either of these parameters are not present, it will replace the contents of /etc/resolv.conf with /etc/resolv.conf.save. By default, PEERDNS and RESOLV_MODS are null.
The /etc/resolv.conf file will be overwritten if any network interfaces use DHCP for activation. To prevent this, ensure such interfaces have PEERDNS=no set in their ifcfg file, for example:
#cat /etc/sysconfig/network-scripts/ifcfg-eth0
TYPE=Ethernet
DEVICE=eth0
BOOTPROTO=dhcp
PEERDNS=no
The ifcfg-file directives DNS1 and DNS2 can also lead to modification of resolv.conf. To prevent this, either remove said directives or use chattr(1) to make resolv.conf immutable to changes, i.e.:
#chattr +i /etc/resolv.conf
