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Mihai
Asked: 2015-05-09 01:22:27 +0800 CST

How do I force NetworkManager to update /etc/resolv.conf?

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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?

redhat

5 Answers

  1. Best Answer

    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

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  2. 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
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  3. 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
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    • 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:

    • Set IPv4 DNS settings to Google DNS entries 8.8.8.8 and 8.8.4.4: sudo nmcli c m eth0 ipv4.dns "8.8.8.8 8.8.4.4"
    • Save changes to system files (like /etc/resolv.conf, etc.) with: sudo nmcli c up eth0

    Bonus:

    • Do the whole thing to a remote server over ssh: ssh remote-server 'sudo nmcli c m eth0 ipv4.dns "8.8.8.8 8.8.4.4" && sudo nmcli c up eth0'
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  5. 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:

    1. 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.

    1. Add whatever settings to the /etc/sysconfig/network-scripts/ifcfg-eth0:0 file are desired to apply to the /etc/resolv.conf file. Example:

    DNS1="8.8.8.8 7.7.7.7"

    DOMAIN="urdomain1.com urdomain2.com"

    1. The new settings in the ifcfg-eth0:0 can be "switched on" (added) in the /etc/resolv.conf by simply running the following command:

    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.

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