nss-myhostname(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | EXAMPLE | SEE ALSO | COLOPHON

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

NAME         top

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

SYNOPSIS         top

       libnss_myhostname.so.2

DESCRIPTION         top

       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.

       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" either between "resolve"
       and "traditional" modules like "dns", or after them. In the first
       version, well-known names like "localhost" and the machine
       hostname are given higher priority than the external
       configuration. This is recommended when the external DNS servers
       and network are not absolutely trusted. In the second version,
       external configuration is given higher priority and
       nss-myhostname only provides a fallback mechanism. This might be
       suitable in closely controlled networks, for example on a company
       LAN.

EXAMPLE         top

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

           passwd:         compat systemd
           group:          compat [SUCCESS=merge] systemd
           shadow:         compat

           # Either (untrusted network, see above):
           hosts:          mymachines resolve [!UNAVAIL=return] files myhostname dns
           # Or (only trusted networks):
           hosts:          mymachines resolve [!UNAVAIL=return] files dns 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         top

       systemd(1), nss-systemd(8), nss-resolve(8), nss-mymachines(8),
       nsswitch.conf(5), getent(1)

COLOPHON         top

       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 2020-12-18.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2020-12-18.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 247                                            NSS-MYHOSTNAME(8)

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