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?

Solution

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

Comments

[2707974]

Do you try to simple add dns server in nm-applet for connection?

[hiro protagonist]

i am in the rescue session - command line only - there is no nm-applet.

[2707974]

Then try to write dns to /etc/resolv.conf. Edit /etc/resolv.conf and add nameserver ip_address_of_dns

[hiro protagonist]

that is the best workaround i could come up with so far - but it changes the configuration on the disk...

[2707974]

You must to change something if you wont dns to work :)

[hiro protagonist]

nope. found a way!

[2707974]

Great, I must remember. Up vote from me.

[Pablo Bianchi]

Moreover, that file stands clearly with a "# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN".

[hiro protagonist]

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).