'\" t
.TH "NSS\-MYHOSTNAME" "8" "" "systemd 241" "nss-myhostname"
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.\" http://bugs.debian.org/507673
.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
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.SH "NAME"
nss-myhostname, libnss_myhostname.so.2 \- Provide hostname resolution for the locally configured system hostname\&.
.SH "SYNOPSIS"
.PP
libnss_myhostname\&.so\&.2
.SH "DESCRIPTION"
.PP
\fBnss\-myhostname\fR
is a plug\-in module for the GNU Name Service Switch (NSS) functionality of the GNU C Library (\fBglibc\fR), primarily providing hostname resolution for the locally configured system hostname as returned by
\fBgethostname\fR(2)\&. The precise hostnames resolved by this module are:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
The local, configured hostname is resolved to all locally configured IP addresses ordered by their scope, or \(em if none are configured \(em the IPv4 address 127\&.0\&.0\&.2 (which is on the local loopback) and the IPv6 address ::1 (which is the local host)\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
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\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
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\&.
.RE
.PP
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
\fBnss\-myhostname\fR
enabled, changing
/etc/hosts
is unnecessary, and on many systems, the file becomes entirely optional\&.
.PP
To activate the NSS modules, add
"myhostname"
to the line starting with
"hosts:"
in
/etc/nsswitch\&.conf\&.
.PP
It is recommended to place
"myhostname"
last in the
nsswitch\&.conf\*(Aq
"hosts:"
line to make sure that this mapping is only used as fallback, and that any DNS or
/etc/hosts
based mapping takes precedence\&.
.SH "EXAMPLE"
.PP
Here is an example
/etc/nsswitch\&.conf
file that enables
\fBnss\-myhostname\fR
correctly:
.sp
.if n \{\
.RS 4
.\}
.nf
passwd:         compat mymachines systemd
group:          compat mymachines systemd
shadow:         compat

hosts:          files mymachines resolve [!UNAVAIL=return] dns \fBmyhostname\fR
networks:       files

protocols:      db files
services:       db files
ethers:         db files
rpc:            db files

netgroup:       nis
.fi
.if n \{\
.RE
.\}
.PP
To test, use
\fBglibc\fR\*(Aqs
\fBgetent\fR
tool:
.sp
.if n \{\
.RS 4
.\}
.nf
$ 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
.fi
.if n \{\
.RE
.\}
.PP
In this case, the local hostname is
\fIomega\fR\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1),
\fBnss-systemd\fR(8),
\fBnss-resolve\fR(8),
\fBnss-mymachines\fR(8),
\fBnsswitch.conf\fR(5),
\fBgetent\fR(1)