Mailing List Archive: resolv.conf full of old info

resolv.conf full of old info

Oct 18, 2022, 3:21 PM

Post #1 of 4 (175 views)

I've noticed that /etc/resolv.conf seems to accumulate obsolete,
useless info as my laptop moves from one network to another. It looks
like dhcpcd adds stuff when a connection comes up, but never removes
it when the connection goes down.

There are search entries and nameserver entries from networks I
haven't been connected to for a long time.

Even when there are no network interfaces up/configured,
/etc/resolv.conf is full of entries -- and none of them are useful or
valid.

I've tried shutting down all of the network interfaces, deleteting all
of the leases from /var/lib/dhcpcd and then removing resolv.conf. The
next time any interface comes up, /etc/resolv.conf is again full of
obsolete stuff along with the valid entries for the interface that has
just come up.

How do you get rid of old entries that show up in resolv.conf?

Re: resolv.conf full of old info [ In reply to ]

grant.b.edwards at gmail

Oct 18, 2022, 5:00 PM

Post #2 of 4 (175 views)

Permalink

On 2022-10-18, Grant Edwards <grant.b.edwards@gmail.com> wrote:

> I've noticed that /etc/resolv.conf seems to accumulate obsolete,
> useless info as my laptop moves from one network to another. It looks
> like dhcpcd adds stuff when a connection comes up, but never removes
> it when the connection goes down.

This appears to be caused by the "persistent" option in dhcpcd.conf,
which is set by default. I commented it out, and now resolv.conf
behaves rationally: it only contains info for network connections that
are up.

Why would dhcpcd have the persistent option enabled by default?

--
Grant

Re: Re: resolv.conf full of old info [ In reply to ]

confabulate at kintzios

Oct 19, 2022, 2:22 AM

Post #3 of 4 (174 views)

Permalink

On Wednesday, 19 October 2022 01:00:31 BST Grant Edwards wrote:
> On 2022-10-18, Grant Edwards <grant.b.edwards@gmail.com> wrote:
> > I've noticed that /etc/resolv.conf seems to accumulate obsolete,
> > useless info as my laptop moves from one network to another. It looks
> > like dhcpcd adds stuff when a connection comes up, but never removes
> > it when the connection goes down.
>
> This appears to be caused by the "persistent" option in dhcpcd.conf,
> which is set by default. I commented it out, and now resolv.conf
> behaves rationally: it only contains info for network connections that
> are up.
>
> Why would dhcpcd have the persistent option enabled by default?
>
> --
> Grant

I think because this causes less breakage in those cases where netmount,
remote syslog-ng, SSH clients, or root mounted NFS is in play? This is what
the man page says about it:

"... dhcpcd normally de-configures the interface and configuration when it
exits. Sometimes, this isn't desirable if, for example, you have root mounted
over NFS or SSH clients connect to this host and they need to be notified of
the host shutting down."

Re: resolv.conf full of old info [ In reply to ]

grant.b.edwards at gmail

Oct 19, 2022, 6:39 AM

Post #4 of 4 (173 views)

Permalink

On 2022-10-19, Michael <confabulate@kintzios.com> wrote:
> On Wednesday, 19 October 2022 01:00:31 BST Grant Edwards wrote:
>> On 2022-10-18, Grant Edwards <grant.b.edwards@gmail.com> wrote:
>>
>> Why would dhcpcd have the persistent option enabled by default?
>
> I think because this causes less breakage in those cases where netmount,
> remote syslog-ng, SSH clients, or root mounted NFS is in play? This is what
> the man page says about it:
>
> "... dhcpcd normally de-configures the interface and configuration when it
> exits. Sometimes, this isn't desirable if, for example, you have root mounted
> over NFS or SSH clients connect to this host and they need to be notified of
> the host shutting down."

I guess that makes sense. What was confusing was that I read the man
page which said it was normally disabled, and since I had never
touched the config file, and wasn't passing the -p option I assumed it
was disabled -- then I finally looked through the default config file,
where it's "nomrally enabled".

--
Grant

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