Difference between revisions of "Domain name resolution"

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{{Move|DNS configuration|Article should describe nsswitch.conf, resolv.conf, caching DNS servers and utilities like dig & drill.|section=Rewrite}}
{{Move|DNS configuration|Article should describe nsswitch.conf, resolv.conf, caching DNS servers and utilities like dig & drill.|section=Rewrite}}
A client for the [[Wikipedia:Domain Name System|Domain Name System]] (DNS) is called a [[Wikipedia:DNS resolver|DNS resolver]].
The configuration file for DNS resolvers is {{ic|/etc/resolv.conf}}. From {{man|5|resolv.conf}}:
The configuration file for DNS resolvers is {{ic|/etc/resolv.conf}}. From {{man|5|resolv.conf}}:

Revision as of 12:17, 21 May 2018

Tango-go-next.pngThis article or section is a candidate for moving to DNS configuration.Tango-go-next.png

Notes: Article should describe nsswitch.conf, resolv.conf, caching DNS servers and utilities like dig & drill. (Discuss in Talk:Domain name resolution#Rewrite)

The configuration file for DNS resolvers is /etc/resolv.conf. From resolv.conf(5):

The resolver is a set of routines in the GNU C library (glibc) that provide access to the Domain Name System. The resolver configuration file contains information that is read by the resolver routines the first time they are invoked by a process. The file is designed to be human readable and contains a list of keywords with values that provide various types of resolver information.
If this file does not exist, only the name server on the local machine will be queried; the domain name is determined from the hostname and the domain search path is constructed from the domain name.

To use #Alternative DNS servers, edit /etc/resolv.conf and add them at the top of the list so they are used first, optionally removing or commenting out other servers. Currently, you may include a maximum of three nameservers.

Note: Changes made to /etc/resolv.conf take effect immediately.
Tip: If you require more flexibility, e.g. more than three nameservers, you can use a local DNS resolver like dnsmasq or unbound. In this case the nameserver IP address will likely be

DNS in Linux

ISPs usually provide working DNS servers. A router may also add an extra DNS server in case it has its own cache server. Switching between DNS servers is transparent for Windows users, because if a DNS server is slow or does not work it will immediately switch to a better one. However, Linux usually takes longer to timeout, which could be the reason why you are getting a delay.


Use drill (provided by package ldns) before any changes, repeat after making the adjustments and compare the query time(s). The following command uses the nameservers set in /etc/resolv.conf:

$ drill www.archlinux.org

You can also specify a specific nameserver's ip address, bypassing the settings in your /etc/resolv.conf:

$ drill @ip.of.name.server www.archlinux.org

For example to test Google's name servers:

$ drill @ www.archlinux.org

To test a local name server (such as unbound) do:

$ drill @ www.archlinux.org

Preserve DNS settings

dhcpcd, netctl, NetworkManager, and various other processes can overwrite /etc/resolv.conf. This is usually desirable behavior, but sometimes DNS settings need to be set manually (e.g. when using a static IP address). There are several ways to accomplish this.

  • If you are using dhcpcd, see #Modify the dhcpcd config below.
  • If you are using netctl and static IP address assignment, do not use the DNS* options in your profile, otherwise resolvconf is called and /etc/resolv.conf overwritten.

Systemd-resolved configuration

systemd-resolved(8) is a systemd service that provides network name resolution to local applications. systemd-resolved has four different modes for handling resolv.conf. We will focus here on the two most relevant modes.

  1. The mode in which systemd-resolved is a client of the /etc/resolv.conf. This mode preserves /etc/resolv.conf and is compatible with the procedures described in this page.
  2. The systemd-resolved's recommended mode of operation: the DNS stub file as indicated below contains both the local stub as the only DNS servers and a list of search domains.
search lan

The service users are advised to redirect the /etc/resolv.conf file to the local stub DNS resolver file /run/systemd/resolve/stub-resolv.conf managed by systemd-resolved. This propagates the systemd managed configuration to all the clients. This can be done by deleting or renaming the existing /etc/resolv.conf and replacing it by a symbolic link to the systemd stub:

# ln -s /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf

In this mode, the DNS servers are provided in the resolved.conf(5) file:


In order to check the DNS actually used by systemd-resolved, the command to use is:

$ systemd-resolve --status
  • To understand the context around the DNS choices and switches, one can turn on detailed debug information for systemd-resolved as described in Systemd#Diagnosing a service.
  • The mode of operation of systemd-resolved is detected automatically, depending on whether /etc/resolv.conf is a symlink to the local stub DNS resolver file or contains server names.

Prevent NetworkManager modifications

Tango-go-next.pngThis article or section is a candidate for moving to NetworkManager#Prevent overwriting of resolv.conf.Tango-go-next.png

Notes: NetworkManager configuration belongs to the NetworkManager article. (Discuss in Talk:Domain name resolution#Rewrite)

To stop NetworkManager from modifying /etc/resolv.conf, edit /etc/NetworkManager/NetworkManager.conf and add the following in the [main] section:


/etc/resolv.conf might be a broken symlink that you will need to remove after doing that. Then, just create a new /etc/resolv.conf file.

NetworkManager also offers hooks via so called dispatcher scripts that can be used to alter the /etc/resolv.conf after network changes. See NetworkManager#Network services with NetworkManager dispatcher and NetworkManager(8) for more information.


openresolv provides a utility resolvconf, which is a framework for managing multiple DNS configurations. See resolvconf(8) and resolvconf.conf(5) for more information.

The configuration is done in /etc/resolvconf.conf and running resolvconf -u will generate /etc/resolv.conf.

Note that NetworkManager can be configured to use openresolv, see NetworkManager#Configure NetworkManager resolv.conf management mode to use resolvconf.

Modify the dhcpcd config

Tango-go-next.pngThis article or section is a candidate for moving to dhcpcd#Prevent overwriting of resolv.conf.Tango-go-next.png

Notes: dhcpcd configuration belongs to the dhcpcd article. (Discuss in Talk:Domain name resolution#Rewrite)

dhcpcd's configuration file may be edited to prevent the dhcpcd daemon from overwriting /etc/resolv.conf. To do this, add the following to the last section of /etc/dhcpcd.conf:

nohook resolv.conf

Alternatively, you can create a file called /etc/resolv.conf.head containing your DNS servers. dhcpcd will prepend this file to the beginning of /etc/resolv.conf.

Or you can configure dhcpcd to use the same DNS servers every time. To do this, add the following line at the end of your /etc/dhcpcd.conf, where dns-server-ip-addressses is a space separated list of DNS IP addresses.

static domain_name_servers=dns-server-ip-addresses

For example, to set it to Google's DNS servers:

static domain_name_servers=

Write-protect resolv.conf

Another way to protect your /etc/resolv.conf from being modified by anything is setting the immutable (write-protection) attribute:

# chattr +i /etc/resolv.conf

Tips and tricks

Limit lookup time

If you are confronted with a very long hostname lookup (may it be in pacman or while browsing), it often helps to define a small timeout after which an alternative nameserver is used. To do so, put the following in /etc/resolv.conf.

options timeout:1

Hostname lookup delayed with IPv6

If you experience a 5 second delay when resolving hostnames it might be due to a DNS-server/Firewall misbehaving and only giving one reply to a parallel A and AAAA request (source). You can fix that by setting the following option in /etc/resolv.conf:

options single-request

Local domain names

If you want to be able to use the hostname of local machine names without the fully qualified domain names, then add a line to resolv.conf with the local domain such as:

domain example.com

That way you can refer to local hosts such as mainmachine1.example.com as simply mainmachine1 when using the ssh command, but the drill command still requires the fully qualified domain names in order to perform lookups.

Alternative DNS servers

Tango-go-next.pngThis article or section is a candidate for moving to Public DNS servers.Tango-go-next.png

Notes: This page describes DNS resolvers, while a list of public DNS servers is relevant it's a different topic. (Discuss in Talk:Domain name resolution#)

Cisco Umbrella (formerly OpenDNS)

OpenDNS provided free alternative nameservers, was bought by Cisco in Nov. 2016 and continues to offer OpenDNS as end-user product of its "Umbrella" product suite with focus on Security Enforcement, Security Intelligence and Web Filtering. The old nameservers still work but are pre-configured to block adult content:

IPv4 nameservers

IPv6 nameservers



Cloudflare provides a service committed to never writing the querying IP addresses to disk and wiping all logs within 24 hours, with the exception of providing data to APNIC labs for research purposes. APNIC and Cloudfare committed to treat all data with high privacy standards in their research agreement statement.

IPv4 nameservers:

IPv6 nameservers:



Comodo provides another IPv4 set, with optional (non-free) web-filtering. Implied in this feature is that the service hijacks the queries.


DNS.WATCH focuses on neutrality and security and provides two servers located in Germany with no logging and with DNSSEC enabled. Note they welcome commercial sponsorship.    # resolver1.dns.watch    # resolver2.dns.watch


Google's nameservers can be used as an alternative:

IPv4 nameservers

IPv6 nameservers



OpenNIC provides free uncensored nameservers located in multiple countries. The full list of public servers is available at servers.opennic.org and a shortlist of nearest nameservers for optimal performance is generated on their home page.

To retrieve a list of nearest nameservers, an API is also available and returns, based on the URL parameters provided, a list of nameservers in the desired format. For example to get the 200 nearest IPv4 servers, one can use https://api.opennicproject.org/geoip/?list&ipv=4&res=200&adm=0&bl&wl.

Alternatively, the anycast servers below can be used; while reliable their latency fluctuates a lot.

IPv4 nameservers (Worldwide Anycast)

IPv6 nameservers (Worldwide Anycast)

  • The use of OpenNIC DNS servers will allow host name resolution in the traditional Top-Level Domain (TLD) registries, but also in OpenNIC or afiliated operated namespaces: .o, .libre, .dyn...
  • The tool opennic-up — automates the renewal of the DNS servers with the most responsive OpenNIC servers
https://github.com/kewlfft/opennic-up || opennic-upAUR


Quad9 is a free DNS service founded by IBM, Packet Clearing House and Global Cyber Alliance; its primary unique feature is a blocklist which avoids resolving known malicious domains. The addresses below are worldwide anycast.

IPv4 nameservers    ## "secure", with blocklist and DNSSEC    ## no blocklist, no DNSSEC

IPv6 nameservers

2620:fe::fe    ## "secure", with blocklist and DNSSEC
2620:fe::10    ## no blocklist, no DNSSEC


UncensoredDNS is a free uncensored DNS service. It is run by a private individual and consists in one anycast served by multiple servers and one unicast node hosted in Denmark.

IPv4 nameservers    ## anycast.censurfridns.dk      ## unicast.censurfridns.dk

IPv6 nameservers

2001:67c:28a4::   ## anycast.censurfridns.dk
2a01:3a0:53:53::  ## unicast.censurfridns.dk
Note: Its servers listen to port 5353 as well as the standard port 53. This can be used in case your ISP hijacks port 53.


Yandex.DNS has servers in Russia, Eastern and Western Europe and has three options, Basic, Safe and Family:

Basic Yandex.DNS - Quick and reliable DNS              # Preferred IPv4 DNS              # Alternate IPv4 DNS

2a02:6b8::feed:0ff     # Preferred IPv6 DNS
2a02:6b8:0:1::feed:0ff # Alternate IPv6 DNS

Safe Yandex.DNS - Protection from virus and fraudulent content             # Preferred IPv4 DNS              # Alternate IPv4 DNS

2a02:6b8::feed:bad     # Preferred IPv6 DNS
2a02:6b8:0:1::feed:bad # Alternate IPv6 DNS

Family Yandex.DNS - Without adult content              # Preferred IPv4 DNS              # Alternate IPv4 DNS

2a02:6b8::feed:a11     # Preferred IPv6 DNS
2a02:6b8:0:1::feed:a11 # Alternate IPv6 DNS

Yandex.DNS' speed is the same in the three modes. In Basic mode, there is no traffic filtering. In Safe mode, protection from infected and fraudulent sites is provided. Family mode enables protection from dangerous sites and blocks sites with adult content.