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NAME | SYNOPSIS | DESCRIPTION | EXAMPLE | SEE ALSO | COLOPHON |
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NSS-MYHOSTNAME(8) nss-myhostname NSS-MYHOSTNAME(8)
nss-myhostname, libnss_myhostname.so.2 - Hostname resolution for
the locally configured system hostname
libnss_myhostname.so.2
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.
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.
systemd(1), nss-systemd(8), nss-resolve(8), nss-mymachines(8),
nsswitch.conf(5), getent(1)
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 2021-04-01. (At that
time, the date of the most recent commit that was found in the
repository was 2021-04-01.) 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 248 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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