NSS-MYMACHINES(8) nss-mymachines NSS-MYMACHINES(8)
NAME
nss-mymachines, libnss_mymachines.so.2 - Hostname resolution for local
container instances
SYNOPSIS
libnss_mymachines.so.2
DESCRIPTION
nss-mymachines is a plug-in module for the GNU Name Service Switch
(NSS) functionality of the GNU C Library (glibc), providing hostname
resolution for the names of containers running locally that are
registered with systemd-machined.service(8). The container names are
resolved to the IP addresses of the specific container, ordered by
their scope. This functionality only applies to containers using
network namespacing (see the description of --private-network in
systemd-nspawn(1)). Note that the name that is resolved is the one
registered with systemd-machined, which may be different than the
hostname configured inside of the container.
Note that this NSS module only makes available names of the containers
running immediately below the current system context. It does not
provide host name resolution for containers running side-by-side with
the invoking system context, or containers further up or down the
container hierarchy. Or in other words, on the host system it provides
host name resolution for the containers running immediately below the
host environment. When used inside a container environment however, it
will not be able to provide name resolution for containers running on
the host (as those are siblings and not children of the current
container environment), but instead only for nested containers running
immediately below its own container environment.
To activate the NSS module, add "mymachines" to the line starting with
"hosts:" in /etc/nsswitch.conf.
It is recommended to place "mymachines" before the "resolve" or "dns"
entry of the "hosts:" line of /etc/nsswitch.conf in order to make sure
that its mappings are preferred over other resolvers such as DNS.
CONFIGURATION IN /ETC/NSSWITCH.CONF
Here is an example /etc/nsswitch.conf file that enables nss-mymachines
correctly:
passwd: compat systemd
group: compat [SUCCESS=merge] systemd
shadow: compat 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
EXAMPLE: MAPPINGS PROVIDED BY NSS-MYMACHINES
The container "rawhide" is spawned using systemd-nspawn(1):
# systemd-nspawn -M rawhide --boot --network-veth --private-users=pick
Spawning container rawhide on /var/lib/machines/rawhide.
Selected user namespace base 20119552 and range 65536.
...
$ machinectl --max-addresses=3
MACHINE CLASS SERVICE OS VERSION ADDRESSES
rawhide container systemd-nspawn fedora 30 169.254.40.164 fe80::94aa:3aff:fe7b:d4b9
$ ping -c1 rawhide
PING rawhide(fe80::94aa:3aff:fe7b:d4b9%ve-rawhide (fe80::94aa:3aff:fe7b:d4b9%ve-rawhide)) 56 data bytes
64 bytes from fe80::94aa:3aff:fe7b:d4b9%ve-rawhide (fe80::94aa:3aff:fe7b:d4b9%ve-rawhide): icmp_seq=1 ttl=64 time=0.045 ms
...
$ ping -c1 -4 rawhide
PING rawhide (169.254.40.164) 56(84) bytes of data.
64 bytes from 169.254.40.164 (169.254.40.164): icmp_seq=1 ttl=64 time=0.064 ms
...
# machinectl shell rawhide /sbin/ip a
Connected to machine rawhide. Press ^] three times within 1s to exit session.
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
...
2: host0@if21: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 96:aa:3a:7b:d4:b9 brd ff:ff:ff:ff:ff:ff link-netnsid 0
inet 169.254.40.164/16 brd 169.254.255.255 scope link host0
valid_lft forever preferred_lft forever
inet6 fe80::94aa:3aff:fe7b:d4b9/64 scope link
valid_lft forever preferred_lft forever
Connection to machine rawhide terminated.
SEE ALSO
systemd(1), systemd-machined.service(8), machinectl(1), nss-systemd(8),
nss-resolve(8), nss-myhostname(8), nsswitch.conf(5), getent(1)
systemd 252 NSS-MYMACHINES(8)
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