NSS-MYHOSTNAME(8)		nss-myhostname		     NSS-MYHOSTNAME(8)

NAME
       nss-myhostname, libnss_myhostname.so.2 - Hostname resolution for the
       locally configured system hostname

SYNOPSIS
       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.

       •   The hostname "_outbound" is resolved to the local IPv4 and IPv6
	   addresses that are most likely used for communication with other
	   hosts. This is the preferred source addresses of default gateways
	   if specified, or determined by requesting a routing decision to the
	   configured default gateways from the kernel and then using the
	   local IP addresses selected by this decision. This hostname is only
	   available if there is at least one local default gateway
	   configured. This assigns a stable hostname to the local outbound IP
	   addresses, useful for referencing them 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" after "files" and before "dns".
       This resolves well-known hostnames like "localhost" and the machine
       hostnames locally. It is consistent with the behaviour of nss-resolve,
       and still allows overriding via /etc/hosts.

       Please keep in mind that nss-myhostname (and nss-resolve) also resolve
       in the other direction — from locally attached IP addresses to
       hostnames. If you rely on that lookup being provided by DNS, you might
       want to order things differently.

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

	   passwd:	   files systemd
	   group:	   files [SUCCESS=merge] systemd
	   shadow:	   files systemd
	   gshadow:	   files systemd

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

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

	   netgroup:	   nis

       To test, use glibc's getent(1) 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)

systemd 258						     NSS-MYHOSTNAME(8)