Ubuntu Manpage: nss-mymachines, libnss_mymachines.so.2 - Provide hostname resolution for local container

Provided by: libnss-mymachines_245.4-4ubuntu3.24_amd64

NAME

       nss-mymachines, libnss_mymachines.so.2 - Provide 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.

The module also provides name resolution for user and group identifiers mapped to
containers. All names from the range allocated to a given container container are exposed
on the host as "vu-container-uid" and "vg-container-gid" (see example below). This
functionality only applies to containers using user namespacing (see the description of
--private-users in systemd-nspawn(1)).

To activate the NSS module, add "mymachines" to the lines starting with "hosts:",
"passwd:" and "group:" in /etc/nsswitch.conf.

It is recommended to place "mymachines" after the "files" or "compat" entry of the
/etc/nsswitch.conf lines to make sure that its mappings are preferred over other resolvers
such as DNS, but so that /etc/hosts, /etc/passwd and /etc/group based mappings take
precedence.

CONFIGURATION IN /ETC/NSSWITCH.CONF

       Here is an example /etc/nsswitch.conf file that enables nss-mymachines correctly:

           passwd:         compat mymachines systemd
           group:          compat mymachines systemd
           shadow:         compat

           hosts:          files mymachines resolve [!UNAVAIL=return] dns myhostname
           networks:       files

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

           netgroup:       nis

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

           $ getent passwd vu-rawhide-0 vu-rawhide-81
           vu-rawhide-0:*:20119552:65534:vu-rawhide-0:/:/usr/sbin/nologin
           vu-rawhide-81:*:20119633:65534:vu-rawhide-81:/:/usr/sbin/nologin

           $ getent group vg-rawhide-0 vg-rawhide-81
           vg-rawhide-0:*:20119552:
           vg-rawhide-81:*:20119633:

           $ ps -o user:15,pid,tty,command -e|grep '^vu-rawhide'
           vu-rawhide-0      692 ?        /lib/systemd/systemd
           vu-rawhide-0      731 ?        /lib/systemd/systemd-journald
           vu-rawhide-192    734 ?        /lib/systemd/systemd-networkd
           vu-rawhide-193    738 ?        /lib/systemd/systemd-resolved
           vu-rawhide-0      742 ?        /lib/systemd/systemd-logind
           vu-rawhide-81     744 ?        /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
           vu-rawhide-0      746 ?        /usr/sbin/sshd -D ...
           vu-rawhide-0      752 ?        /lib/systemd/systemd --user
           vu-rawhide-0      753 ?        (sd-pam)
           vu-rawhide-0     1628 ?        login -- zbyszek
           vu-rawhide-1000  1630 ?        /lib/systemd/systemd --user
           vu-rawhide-1000  1631 ?        (sd-pam)
           vu-rawhide-1000  1637 pts/8    -zsh

           $ 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.

NAME

SYNOPSIS

DESCRIPTION

CONFIGURATION IN /ETC/NSSWITCH.CONF

MAPPINGS PROVIDED BY NSS-MYMACHINES

SEE ALSO