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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.
• 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.
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.
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 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
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 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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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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