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| The '''Name Service Switch''' ('''NSS''') file (`/etc/nsswitch.conf`) defines the order of operations for various services, among them being name resolution. | The [[Linux/NsSwitchConf|Name Service Switch (NSS) configuration file]] (`/etc/nsswitch.conf`) defines the order of operations for various services, among them being name resolution. |
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| See [[Linux/nsswitch.conf|here]] for more details on configuring `/etc/nsswitch`. |
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| The '''hosts''' file (`/etc/hosts`) is a list of addresses and names, especially for local hosts and machines. A basic hosts file looks like: | The [[Linux/Hosts|hosts file]] (`/etc/hosts`) is a list of addresses and names, especially for local hosts and machines. A basic hosts file looks like: |
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| See [[Linux/hosts|here]] for more details on configuring `/etc/hosts`. |
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| The '''resolver''' configuration file (`/etc/resolv.conf`) is a list of nameservers to query for name resolution. The file is read sequentially for up to 3 nameservers for each lookup. As such, changes are effective immediately. | The [[Linux/ResolvConf|resolver configuration file]] (`/etc/resolv.conf`) is a list of nameservers to query for name resolution. Changes are immediately effective. |
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| See [[Linux/resolv.conf|here]] for more details on configuring `/etc/resolv.conf`. |
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| * [[Linux/SystemdResolved|systemd-resolved]] and it's userland utility `resolvectl(1)` * [[Linux/SystemdResolved#ResolveConf|systemd-resolveconf]] * [[OpenResolv|openresolve]] * [[Dhcpcd|dhcpcd]] * [[NetworkManager]] |
* [[Linux/SystemdResolved|systemd-resolved(8)]] and it's userland utility `resolvectl(1)` * [[Linux/SystemdResolved#ResolveConf|systemd-resolveconf(8)]] * [[OpenResolv|openresolve]] with [[Linux/ResolvConfConf|resolveconf.conf(5)]] * [[Dhcpcd|dhcpcd(8)]] * [[NetworkManager|NetworkManager(8)]] |
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| * `dig(1)` (see [[Bind]]) used as `dig @SERVER NAME TYPE` | * [[Bind/Dig|dig(1)]] |
DNS on Linux
Domain Name Resolution (DNS) on Linux is done in a very similar way to DNS on BSD. It is worth reiterating that DNS was invented for BSD.
Contents
Name resolution
Name Service Switch
The Name Service Switch (NSS) configuration file (/etc/nsswitch.conf) defines the order of operations for various services, among them being name resolution.
A minimal configuration looks like...
hosts: files dns
This configuration will require a fully configured hosts file, as seen below.
Consider instead this configuration, which makes use of libraries and services from the systemd project. This will enable some omissions from the hosts file.
hosts: files mymachines myhostname dns
Hosts
The hosts file (/etc/hosts) is a list of addresses and names, especially for local hosts and machines. A basic hosts file looks like:
127.0.0.1 localhost
Resolver
The resolver configuration file (/etc/resolv.conf) is a list of nameservers to query for name resolution. Changes are immediately effective.
If the resolver file is being configured directly, then it should look like:
nameserver 8.8.8.8
Services that manipulate the resolver file include:
systemd-resolved(8) and it's userland utility resolvectl(1)
Utilities
drill(1), used as drill NAME @SERVER TYPE
Multicast name resolution
Multicast domain name resolution (mDNS) is an expansion of the DNS protocol. An mDNS broadcaster makes use of port 5353 and resolves names in the .local domain.
Note that there is also partial/coincidental support for link-local multicast name resolution (LLMNR) in many of the Linux implementations of mDNS. LLMNR is a similar but deliberately incompatible protocol (using port 5355) and also with a limited scope for features.