change DNS server in a non-persistent way (on the command-line) [rescue mode]

Question

is there a way i can change the DNS server on the command-line without having to change anything on the disk?

i recently booted into the rescue session and i got an IP address (using DHCP) but no DNS server. as my network config is usually done with the nm-applet in the desktop session and not in /etc/network/interfaces i would like to be able to provide a DNS server just for this rescue session and not write anything on disk.

this is usually possible by editing /run/resolvconf/resolv.conf. but resolvconf seems not to be running in the ubuntu 14.04 rescue session.

i was hoping there was something similar to the network configuration where i can configure an interface without having to edit a file:

# ifconfig eth0 192.168.2.5 netmask 255.255.255.0
# route add default gw 192.168.2.1

is there a way to do this for DNS in a rescue session on ubuntu 14.04?

Do you try to simple add `dns` server in `nm-applet` for connection? — 2707974, Oct 06 '15 at 07:05
i am in the rescue session - command line only - there is no `nm-applet`. — hiro protagonist, Oct 06 '15 at 07:06
Then try to write dns to `/etc/resolv.conf`. Edit `/etc/resolv.conf` and add `nameserver ip_address_of_dns` — 2707974, Oct 06 '15 at 07:12
that is the best workaround i could come up with so far - but it changes the configuration on the disk... — hiro protagonist, Oct 06 '15 at 07:14

hiro protagonist · Accepted Answer · 2019-07-02T08:50:32.060

7

i found a way to do this:

kill the dns service (there may be a more subtle way?)

# killall dnsmasq

restart the service using the desired upstream server:

# dnsmasq --server=192.168.2.1

on a newer ubuntu (one with systemd) this would be:

# systemd-resolve -i enp0s31f6 --set-dns=192.168.2.1  # --set-dnssec=true

check with:

# systemd-resolve --status

edited Jul 02 '19 at 08:50

answered Oct 06 '15 at 09:02

hiro protagonist

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score 0 · Answer 2 · edited Aug 22 '18 at 03:02

0

To get this to work, I added au.archive.ubuntu.com to the /etc/hosts file with an IP address I got from pinging it on my PC.

Then did apt update and it resolved.

edited Aug 22 '18 at 03:02

Stephen Rauch

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answered Aug 21 '18 at 23:52

Dan

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this will then only resolve that particular domain. any other DNS request will remain unresolved. but i agree, `apt` will work in the rescue session (but nothing else that needs DNS). – hiro protagonist Aug 22 '18 at 06:27

score 0 · Answer 3 · answered Oct 06 '15 at 07:31

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Navigate to this directory /etc/resolvconf/resolv.conf.d edit the head file using vi or vim with su privilege

sudo vi /etc/resolvconf/resolv.conf.d/head

add the following lines to the file

nameserver *DNS server IP*

save the file and use resolvconf utility to set the static DNS server address you entered by the following command

sudo resolvconf -u

answered Oct 06 '15 at 07:31

404

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thanks. but this requires writing on the disk. and in the rescue session `resolvconf` complains: `Error: /run/resolvconf/interface either does not exist or is not a directory`. removing the link `/etc/resolv.conf` and then writing directly into a file of that name seems simpler. – hiro protagonist Oct 06 '15 at 08:50
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Moreover, that file stands clearly with a "`# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN`". – Pablo Bianchi Jul 14 '17 at 00:41

change DNS server in a non-persistent way (on the command-line) [rescue mode]

3 Answers3