nss-myhostname

systemd
Developer Lennart Poettering lennart@poettering.net
nss-myhostname 8
nss-myhostname libnss_myhostname.so.2 Provide hostname resolution for the locally configured system hostname.

`libnss_myhostname.so.2`

## Description

`nss-myhostname` is a plug-in module for the GNU Name Service Switch (NSS) functionality of the GNU C Library (`glibc`), primarily providing hostname resolution for the locally configured system hostname as returned by gethostname 2. The precise hostnames resolved by this module are:

- The local, configured hostname is resolved to all locally configured IP addresses ordered by their scope, or — if none are configured — the IPv4 address 127.0.0.2 (which is on the local loopback) and the IPv6 address ::1 (which is the local host).

- The hostnames `localhost` and `localhost.localdomain` (as well as any hostname ending in `.localhost` or `.localhost.localdomain`) are resolved to the IP addresses 127.0.0.1 and ::1.

- The hostname `_gateway` is resolved to all current default routing gateway addresses, ordered by their metric. This assigns a stable hostname to the current gateway, useful for referencing it independently of the current network configuration state.

Various software relies on an always-resolvable local hostname. When using dynamic hostnames, this is traditionally achieved by patching `/etc/hosts` at the same time as changing the hostname. This is problematic since it requires a writable `/etc` file system and is fragile because the file might be edited by the administrator at the same time. With `nss-myhostname` enabled, changing `/etc/hosts` is unnecessary, and on many systems, the file becomes entirely optional.

To activate the NSS modules, add `myhostname` to the line starting with `hosts:` in `/etc/nsswitch.conf`.

It is recommended to place `myhostname` last in the `nsswitch.conf`' `hosts:` line to make sure that this mapping is only used as fallback, and that any DNS or `/etc/hosts` based mapping takes precedence.

## Example

Here is an example `/etc/nsswitch.conf` file that enables `nss-myhostname` correctly:

    passwd:         compat mymachines systemd
    group:          compat mymachines systemd
    shadow:         compat

    hosts:          files mymachines resolve [!UNAVAIL=return] dns myhostname
    networks:       files

    protocols:      db files
    services:       db files
    ethers:         db files
    rpc:            db files

    netgroup:       nis

To test, use `glibc`'s `getent` tool:

    $ getent ahosts `hostname`
    ::1       STREAM omega
    ::1       DGRAM
    ::1       RAW
    127.0.0.2       STREAM
    127.0.0.2       DGRAM
    127.0.0.2       RAW

In this case, the local hostname is `omega`.

## See Also

systemd 1, nss-systemd 8, nss-resolve 8, nss-mymachines 8, nsswitch.conf 5, getent 1