Unitrends Appliance DNS Servers change after a reboot/network restart.

ISSUE

DNS servers in /etc/resolv.conf change after a reboot/network service restart.

You would also see messages shown below in the /var/log/messages file:

Oct 10 12:40:52 hostname NET[22961]: /etc/sysconfig/network-scripts/ifdown-post : updated /etc/resolv.conf
Oct 10 12:40:57 hostname NET[23256]: /etc/sysconfig/network-scripts/ifup-post : updated /etc/resolv.conf

RESOLUTION

How to make entries in /etc/resolv.conf permanent

1. 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

2. 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

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