Ubuntu 16.10+ uses
systemd-resolved as DNS resolver.
I prefer the setup 16.04 uses,
dnsmasq as the resolver.
How can I do that on 16.10+, especially on 17.04?
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dnsmasq packages are still available in 16.10 and 17.04.
dnsmasq and dependencies (or at least download their packages) before disabling
sudo apt-get install dnsmasq
systemd-resolved and verify
dnsmasq is running:
sudo systemctl stop systemd-resolved sudo systemctl disable systemd-resolved systemctl status dnsmasq
dnsmasq to taste. After applying your settings, restart
sudo systemctl stop dnsmasq sudo systemctl start dnsmasq
After step 2 you might be without a working system resolver until step 3 is complete. You may need to restart the networking subsystem (or simply reboot) to get
dnsmasq functioning with the default configs. In my testing, adding a known DNS server to
/etc/dnsmasq.conf and restarting
dnsmasq was enough to get it working in a liveCD environment.
In addition to the answer of @quixotic:
Make sure you have in /etc/NetworkManager/NetworkManager.conf :
if you need to add it, restart NetworkManager like this:
sudo systemctl restart NetworkManager
/etc/resolv.conf needs to be a symlink to
/var/run/NetworkManager/resolv.conf . could be done like this
sudo rm /etc/resolv.conf; sudo ln -s /var/run/NetworkManager/resolv.conf /etc/resolv.conf
For (X)Ubuntu 18.04 (see my answer at stackexchange).
Here is copy of it (should I make a copy?)
Here is solution for (X)Ubuntu 18.04 Bionic.
sudo apt install dnsmasq
Disable systemd-resolved listener on port 53 (do not touch /etc/systemd/resolved.conf, because it may be overwritten on upgrade):
$ cat /etc/systemd/resolved.conf.d/noresolved.conf [Resolve] DNSStubListener=no
and restart it
$ sudo systemctl restart systemd-resolved
(alternatively disable it completely by
$ sudo systemctl disable systemd-resolved.service)
Delete /etc/resolv.conf and create again. This is important, because resolv.conf is a symbolic link to /run/systemd/resolve/stub-resolv.conf by default. If you will not delete symbolic link, the file will be overwritten by systemd on reboot (even though we disabled systemd-resolved!). Also NetworkManager (NM) checks if it is a symbolic link to detect systemd-resolved configuration.
$ sudo rm /etc/resolv.conf $ sudo touch /etc/resolv.conf
Disable overwriting of /etc/resolv.conf by NM (there is also an option rc-manager, but it does not work, despite it is described in a manual):
$ cat /etc/NetworkManager/conf.d/disableresolv.conf [main] dns=none
and restart it:
$ sudo systemctl restart NetworkManager
Tell dnsmasq to use resolv.conf from NM:
$ cat /etc/dnsmasq.d/nmresolv.conf resolv-file=/var/run/NetworkManager/resolv.conf
and restart it:
$ sudo systemctl restart dnsmasq
Use dnsmasq for resolving:
$ cat /etc/resolv.conf # Use local dnsmasq for resolving nameserver 127.0.0.1
According to the manual of systemd-resolved, systemd-resolved provides with name resolution services via three different interfaces:
The glibc getaddrinfo(3) API as defined by RFC3493 and its related resolver functions, including gethostbyname(3). This API is widely supported, including beyond the Linux platform. In its current form it does not expose DNSSEC validation status information however, and is synchronous only. This API is backed by the glibc Name Service Switch (nss(5)). Usage of the glibc NSS module nss-resolve(8) is required in order to allow glibc's NSS resolver functions to resolve host names via systemd-resolved.
It seems that the first two interfaces won't interfere in normal DNS resolution and for me the problem is likely to reside on the third.
In the manual of nss-resolve:
To activate the NSS module, add "resolve" to the line starting with "hosts:" in /etc/nsswitch.conf. Specifically, it is recommended to place "resolve" early in /etc/nsswitch.conf's "hosts:" line (but after the "files" or "mymachines" entries), right before the "dns" entry if it exists, followed by "[!UNAVAIL=return]", to ensure DNS queries are always routed via systemd-resolved(8) if it is running, but are routed to nss-dns if this service is not available
So what is needed is to make "dns" precedes "resolve" in "host:" line of /etc/nsswitch.conf. And then
getaddrinfo should simply adhere to /etc/resolv.conf .
This solution only prevents systemd-resolved from handling all the DNS resolution requests and is not restricted to a specific network manager. And it also makes sure LLMNR and mDNS service are operating normally.
( I am not fair familiar with how name resolution works under Linux and also unsure about what I understood from these manuals. Pleaes point out if I got something wrong. Thx :) )