CentOS - Feb 2020 - From network-scripts to NetworkManager on a router : questions

Le 18/02/2020 ? 12:28, Anand Buddhdev a ?crit?:
> Neither. The DNS configuration should not normally be bound to a
> specific interface, so don't configure it with any interface. If you
do,
> and that interface goes down, your DNS config also disappears.
I would like to do that very much, only NetworkManager makes you jump through 
burning loops to do so.

With network-scripts, it was just a matter of editing resolv.conf with 
nameserver and search domain directives.

I can't do that anymore, because /etc/resolv.conf gets squashed by 
NetworkManager. If I don't fill in DNS information for the interfaces, then
all
I get is an empty "#Generated by NetworkManager" line.

On the other hand, using nmtui, the only place where I can actually fill in DNS 
information is in the interface-specific dialogs.

After googling around for this problem, it looks like I'm not the only one 
scratching my head.

Any suggestions ?

Niki

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On 18/02/2020 16:37, Nicolas Kovacs wrote:
> I can't do that anymore, because /etc/resolv.conf gets squashed by
> NetworkManager. If I don't fill in DNS information for the interfaces,
> then all I get is an empty "#Generated by NetworkManager" line.
Oh yes. Are you still sure you want to use NetworkManager? It's a pain!
> On the other hand, using nmtui, the only place where I can actually fill
> in DNS information is in the interface-specific dialogs.
> 
> After googling around for this problem, it looks like I'm not the only
> one scratching my head.
> 
> Any suggestions ?
Yes. Do this:

# cat >/etc/NetworkManager/conf.d/dns.conf <<EOF
[main]
rc-manager=unmanaged
EOF

# systemctl reload NetworkManager

This tells NetworkManager to leave /etc/resolv.conf alone. Now you can
put whatever you like in /etc/resolv.conf, and it will be left untouched.

Regards,
Anand

On 2/18/20 9:37 AM, Nicolas Kovacs wrote:
> Le 18/02/2020 ? 12:28, Anand Buddhdev a ?crit?:
>> Neither. The DNS configuration should not normally be bound to a
>> specific interface, so don't configure it with any interface. If
you do,
>> and that interface goes down, your DNS config also disappears.
> 
> I would like to do that very much, only NetworkManager makes you jump
> through burning loops to do so.
> 
> With network-scripts, it was just a matter of editing resolv.conf with
> nameserver and search domain directives.
> 
> I can't do that anymore, because /etc/resolv.conf gets squashed by
> NetworkManager. If I don't fill in DNS information for the interfaces,
> then all I get is an empty "#Generated by NetworkManager" line.
> 
> On the other hand, using nmtui, the only place where I can actually fill
> in DNS information is in the interface-specific dialogs.
Or use 'nmcli con mod <interface_name> ipv4.dns
"8.8.8.8"'

or edit:

/etc/sysconfig/network-scripts/ifcfg-<interface-name>
> 
> After googling around for this problem, it looks like I'm not the only
> one scratching my head.
> 
> Any suggestions ?
> 
> Niki
> 

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Le 18/02/2020 ? 16:51, Anand Buddhdev a ?crit?:
> This tells NetworkManager to leave /etc/resolv.conf alone. Now you can
> put whatever you like in /etc/resolv.conf, and it will be left untouched.
I just found the answer after some more experimenting.

1. If you put some DNS information in any of your ifcfg-* interfaces, 
then NetworkManager will overwrite /etc/resolv.conf with whatever it 
find in there.

   BUT...

2. If there is no DNS information in any of the ifcfg-* files, then 
NetworkManager will leave your manually edited /etc/resolv.conf 
configuration untouched. And this is the default behavior, no need to 
configure it specifically.

Problem solved. :o)

Thanks very much to everybody in this thread for your contribution.

Niki

-- 
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T?l. : 04 66 63 10 32
Mob. : 06 51 80 12 12

On Tue, Feb 18, 2020 at 04:37:29PM +0100, Nicolas Kovacs
wrote:
>
> Le 18/02/2020 ? 12:28, Anand Buddhdev a ?crit?:
> > Neither. The DNS configuration should not normally be bound to a
> > specific interface, so don't configure it with any interface. If
you do,
> > and that interface goes down, your DNS config also disappears.
> 
> I would like to do that very much, only NetworkManager makes you jump
> through burning loops to do so.
> 
> With network-scripts, it was just a matter of editing resolv.conf with
> nameserver and search domain directives.
> 
> I can't do that anymore, because /etc/resolv.conf gets squashed by
> NetworkManager. If I don't fill in DNS information for the interfaces,
then
> all I get is an empty "#Generated by NetworkManager" line.
> 
> On the other hand, using nmtui, the only place where I can actually fill in
> DNS information is in the interface-specific dialogs.
> 
> After googling around for this problem, it looks like I'm not the only
one
> scratching my head.
According to 'man nm-settings-ifcfg-rh', PEERDNS=no is the old
network-services services mechanism for not changing /etc/resolv.conf,
while in NM it just means never add automatic nameservers to
resolv.conf from DHCP, PPP, VPN, etc.  Turning off all DNS
updates means adding:

[main]
dns=none

... to the NetworkManager.conf (or preferably in an
/etc/NetworkManager/conf.d/ file) is probably going to be the most
effective way.  I've seen PEERDNS=no make NetworkManager not overwrite
my resolv.conf but maybe I should be extra careful and drop in a
config file that turns off all dns updating features of
NetworkManager. 

-- 
Jonathan Billings <billings at negate.org>

Le 18/02/2020 ? 16:51, Anand Buddhdev a ?crit?:
> Oh yes. Are you still sure you want to use NetworkManager? It's a pain!
As much as I'm a firm believer in the KISS principle, I don't like to
"swim
against the current". As someone on this list said it earlier, Red Hat
provides
a certain set of tools meant to be used. And since the official guide 
"Considerations in adopting RHEL 8" explicitly states that network
scripts are
considered obsolete, I thought I'd do my best to wrap my head around this
new
way of doing things, like I did before with systemd.

Cheers,

Niki

-- 
Microlinux - Solutions informatiques durables
7, place de l'?glise - 30730 Montpezat
Site : https://www.microlinux.fr
Mail : info at microlinux.fr
T?l. : 04 66 63 10 32
Mob. : 06 51 80 12 12

Le 18/02/2020 ? 17:43, Jonathan Billings a ?crit?:
> According to 'man nm-settings-ifcfg-rh', PEERDNS=no is the old
> network-services services mechanism for not changing /etc/resolv.conf,
> while in NM it just means never add automatic nameservers to
> resolv.conf from DHCP, PPP, VPN, etc.  Turning off all DNS
> updates means adding:
> 
> [main]
> dns=none
> 
> ... to the NetworkManager.conf (or preferably in an
> /etc/NetworkManager/conf.d/  file) is probably going to be the most
> effective way.  I've seen PEERDNS=no make NetworkManager not overwrite
> my resolv.conf but maybe I should be extra careful and drop in a
> config file that turns off all dns updating features of
> NetworkManager.
See my previous mail on that subject.

tl;dr : as long as you don't provide any DNS information for any of the 
interfaces, /etc/resolv.conf does *not* get overwritten.

-- 
Microlinux - Solutions informatiques durables
7, place de l'?glise - 30730 Montpezat
Site : https://www.microlinux.fr
Mail : info at microlinux.fr
T?l. : 04 66 63 10 32
Mob. : 06 51 80 12 12