nss-myhostname

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## Name

nss-myhostname, libnss_myhostname.so.2 — Provide hostname resolution for the locally configured system hostname.

## Synopsis

`libnss_myhostname.so.2`

## Description

nss-myhostname is a plugin 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 hostname "`localhost`" is 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, "`myhostname`" has to be added to the line starting with "`hosts:`" in `/etc/nsswitch.conf`.

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

## Example

Here's an example `/etc/nsswitch.conf` file, that enables myhostname correctly:

    passwd:   compat
    group:    compat
    shadow:   compat

    hosts:    files dns mymachines 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-mymachines(8), nsswitch.conf(5), getent(1)