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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 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)
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