nss-myhostname(8) — Linux manual page

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 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)

COLOPHON

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
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       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 257~devel                                      NSS-MYHOSTNAME(8)

Pages that refer to this page: systemd.directives(7), systemd.index(7), nss-mymachines(8), nss-resolve(8), nss-systemd(8)

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