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 257.4                                                                                  NSS-MYHOSTNAME(8)