Re: NetworkManager, dns= and resolv.conf override

[Thomas HUMMEL <thomas hummel pasteur fr>]

On 3/12/20 2:05 PM, Thomas HUMMEL wrote:
> Hello Thomas, Hello everybody,
>
> In short : in a setup where I don't state any 'dns=' NM directive, I 
> don't understand why /etc/resolv.conf (file, not symlink) is not overriden.

Sorry to insist : any insight about this ?

thanks for your help...
> I'm running CentOS-8.1 on HPC compute nodes provisionned by the xCAT 
> software.
> Basically nodes PXE-boot and download a stateless CentOS-8.1 image.
>
> xCAT provides a so called 'postscript' mechanism (called confignetwork 
> -s) to turn the dynamically (DHCP) assigned node's ip address into a 
> static ip address. It does this by creating an additionnal NM profile 
> with higher autoconnect priority.
>
> for instance :
>
> - profile initially retrieved by PXE/DHCP :
>
> # cat /etc/sysconfig/network-scripts/ifcfg-enp33s0f0
> DEVICE=enp33s0f0
> BOOTPROTO=dhcp
> HWADDR=ac:1f:6b:c8:ee:16
> ONBOOT=yes
>
> - higher priority profile after xCAT 'confignetwork -s' script is run :
>
> # cat /etc/sysconfig/network-scripts/ifcfg-xcat-enp33s0f0
> TYPE=Ethernet
> PROXY_METHOD=none
> BROWSER_ONLY=no
> BOOTPROTO=none
> IPADDR=192.168.152.3
> PREFIX=20
> DEFROUTE=yes
> IPV4_FAILURE_FATAL=no
> IPV6INIT=yes
> IPV6_AUTOCONF=yes
> IPV6_DEFROUTE=yes
> IPV6_FAILURE_FATAL=no
> IPV6_ADDR_GEN_MODE=stable-privacy
> NAME=xcat-enp33s0f0
> UUID=9de3e814-a286-44e9-b66d-3cc14694d808
> DEVICE=enp33s0f0
> ONBOOT=yes
> AUTOCONNECT_PRIORITY=9
> MTU=1500
>
> # Expected and working behavios :
>
> What I experienced is that first the node gets via DHCP, as expected, a 
> working /etc/resolv.conf file and then after xCAT confignetwork -s 
> postscript is run, the new profile is loaded and up but /etc/resolv.conf 
> is empty as, as can be seen above, the profile does not provide any dns 
> properties.
>
> I worked around this by adding 'dns=none' in a NetworkManager .conf 
> file. And it worked : the /etc/resolv.conf file initially written by 
> DHCP was left untouched.
>
> # Unexpected and unexplained behavior :
>
> What I don't understand is that, then if I manually remove the 
> 'dns=none' setting and either restart NM and/or reload+reactivate the 
> profile, /etc/resolv.conf is not, as I was expecting, emptied by NM.
>
> Can you help me figure out what I am missing ?
>
> Thanks for your help
>
> --
> Thomas HUMMEL
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