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 2020-09-18.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-09-18.)  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 246                                                NSS-MYHOSTNAME(8)

Pages that refer to this page: 30-systemd-environment-d-generator(7)systemd.directives(7)systemd.index(7)libnss_mymachines.so.2(8)libnss_resolve.so.2(8)libnss_systemd.so.2(8)nss-mymachines(8)nss-resolve(8)nss-systemd(8)