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 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 "file" 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)