I am working on a project that involves an IOT device (the now deprecated Intel Galileo). I am looking at hardening these devices and I noticed that the systemd-resolved service is listening on all interfaces (

root@hostname:~# netstat -altnp
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0  *               LISTEN      240/systemd-resolve

After reading the freedesktop.org description of the service here, it states that,

systemd-resolved is a system service that provides network name resolution to local applications.

I ran a test where I ran ping to google.com where the systemd-resolved was running. I then disabled the service and sent a ping to yahoo.com. There was no packet loss for either request.

My question(s) are as follows:

What is this service doing?

If it is providing name resolution to local applications, why does it listen on the interface?

Is this a security concern?

What are the potential impacts of disabling this service?

Thanks in advance for any information / help. Apologies if I have not complied with question format, first time post. Please edit as required.

  • There is currently a security issue with systemd-resolver and so I would keep up to date with patches for this service and in the mean time disable it is possible. Best option would be to create a test rig and test that everything works as expected. Systemd-resolver is designed for systemd inter process communication but many of the legacy applications haven't been written for systemd and so won't reference systemd-resolver. – Raman Sailopal Jul 3 '17 at 20:55
  • 1
    Thanks for the reply @Raman. We are in the process of testing disabling. I was aware of an exploit issued on Ubuntu wrt to systemd-resolved. Thanks again – jeeves Jul 6 '17 at 10:35

systemd-resolved is needed by systemd. Unless you're installing an alternative DNS resolver, you should keep it.

It's important to note that it is actually listening for UDP packets on to do DNS resolution for you:

# netstat -npa | grep systemd-resolve
tcp        0      0  *               LISTEN      205/systemd-resolve
tcp6       0      0 :::5355                 :::*                    LISTEN      205/systemd-resolve
udp        0      0 *                           205/systemd-resolve
udp        0      0  *                           205/systemd-resolve
udp6       0      0 :::5355                 :::*                                205/systemd-resolve

The port 5355 sockets are to implement Link-Local Multicast Name Resolution (LLMNR) which is a feature only useful in LANs.

To disable it, edit /etc/systemd/resolved.conf and change the line




and then restart the service with service systemd-resolved restart and check again:

# netstat -npa | grep systemd-resolve
udp        0      0 *                           404/systemd-resolve

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