# resolv.conf

Related articles

- Improving performance#Network

The configuration file for DNS resolvers is `/etc/resolv.conf`. From its man page:

  The resolver is a set of routines in the C library that provide access to the Internet Domain Name System (DNS). 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.

## DNS in Linux

Your ISP (usually) provides working DNS servers, and a router may also add an extra DNS server in case you have your own cache server. Switching between DNS servers does not represent a problem 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.

### Testing

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 www5.yahoo.com

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

    $ drill @ip.of.name.server www5.yahoo.com

For example to test Google's name servers:

    $ drill @8.8.8.8 www5.yahoo.com

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

    $ drill @127.0.0.1 www5.yahoo.com

## Alternative DNS servers

To use alternative DNS servers, edit `/etc/resolv.conf` and add them to the top of the file so they are used first, optionally removing or commenting out already listed servers. Currently, you may include a maximum of three `nameserver` lines.

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 locally caching nameserver/resolver like dnsmasq or unbound. Using a local DNS caching resolver, most likely you will not set the `nameserver` to the actual DNS server but to `127.0.0.1`. See the article for the program you are using for DNS caching.

### OpenNIC

OpenNIC provides free uncensored nameservers with additional features.

Tip: OpenNIC offers many different nameservers located in multiple countries. Pick some of the nearest nameservers for optimal performance.

    # OpenNIC IPv4 nameservers (US)
    nameserver 107.170.95.180
    nameserver 75.127.14.107

### OpenDNS

OpenDNS provides free alternative nameservers:

    # OpenDNS IPv4 nameservers
    nameserver 208.67.222.222
    nameserver 208.67.220.220

    # OpenDNS IPv6 nameservers
    nameserver 2620:0:ccc::2
    nameserver 2620:0:ccd::2

### Google

Google's nameservers can be used as an alternative:

    # Google IPv4 nameservers
    nameserver 8.8.8.8
    nameserver 8.8.4.4

    # Google IPv6 nameservers
    nameserver 2001:4860:4860::8888
    nameserver 2001:4860:4860::8844

### Comodo

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

    # Comodo nameservers
    nameserver 8.26.56.26
    nameserver 8.20.247.20

### Yandex

Yandex.DNS have three options:

    # Basic Yandex.DNS - Quick and reliable DNS
    nameserver 77.88.8.8              # Preferred IPv4 DNS
    nameserver 77.88.8.1              # Alternate IPv4 DNS

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

    # Safe Yandex.DNS - Protection from virus and fraudulent content
    nameserver 77.88.8.88             # Preferred IPv4 DNS
    nameserver 77.88.8.2              # Alternate IPv4 DNS

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

    # Family Yandex.DNS - Without adult content
    nameserver 77.88.8.7              # Preferred IPv4 DNS
    nameserver 77.88.8.3              # Alternate IPv4 DNS

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

Yandex.DNS' speed is the same in all 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.

### UncensoredDNS

UncensoredDNS is a free uncensored DNS resolver who also answers queries on port 5353 if you are behind a firewall blocking outgoing port 53.

    # censurfridns.dk IPv4 nameservers
    nameserver 91.239.100.100    ## anycast.censurfridns.dk
    nameserver 89.233.43.71      ## ns1.censurfridns.dk

    # censurfridns.dk IPv6 nameservers
    nameserver 2001:67c:28a4::             ## anycast.censurfridns.dk
    nameserver 2002:d596:2a92:1:71:53::    ## ns1.censurfridns.dk

## 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.

### With NetworkManager

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

    dns=none

`/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.

### Using openresolv

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

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

### Modify the dhcpcd config

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`:

    static domain_name_servers=8.8.4.4 8.8.8.8

### Write-protect /etc/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

### Use timeout option to reduce hostname 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

## Tips and tricks

### 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.

Category:

- Domain Name System