`libnss_systemd.so.2` ( 8 )

разрешение имен пользователей и групп UNIX для поиска пользователей / групп через Varlink (UNIX user and group name resolution for user/group lookup via Varlink)

Имя (Name)

nss-systemd, libnss_systemd.so.2 - UNIX user and group name
       resolution for user/group lookup via Varlink

Синопсис (Synopsis)

libnss_systemd.so.2

Описание (Description)

nss-systemd is a plug-in module for the GNU Name Service Switch (NSS) functionality of the GNU C Library (glibc), providing UNIX user and group name resolution for services implementing the User/Group Record Lookup API via Varlink[1], such as the system and service manager systemd(1) (for its DynamicUser= feature, see systemd.exec(5) for details), systemd-homed.service(8), or systemd-machined.service(8).

This module also ensures that the root and nobody users and groups (i.e. the users/groups with the UIDs/GIDs 0 and 65534) remain resolvable at all times, even if they aren't listed in /etc/passwd or /etc/group, or if these files are missing.

This module preferably utilizes systemd-userdbd.service(8) for resolving users and groups, but also works without the service running.

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

It is recommended to place "systemd" after the "files" or "compat" entry of the /etc/nsswitch.conf lines so that /etc/passwd, /etc/group, /etc/shadow and /etc/gshadow based mappings take precedence.

STATIC DROP-IN JSON USER/GROUP RECORDS

Besides user/group records acquired via the aforementioned
       Varlink IPC interfaces and the synthesized root and nobody
       accounts, this module also makes user and group accounts
       available to the system that are defined in static drop-in files
       in the /etc/userdb/, /run/userdb/, /run/host/userdb/ and
       /usr/lib/userdb/ directories.

       This is a simple mechanism to provide static user and group
       records via JSON drop-in files. Such user records should be
       defined in the format described by the JSON User Records[2]
       specification and be placed in one of the aforementioned
       directories under a file name composed of the user name suffixed
       with .user, with a world-readable access mode. A symlink named
       after the user record's UID formatted in decimal and suffixed
       with .user pointing to the primary record file should be created
       as well, in order to allow both lookups by username and by UID.
       Privileged user record data (e.g. hashed UNIX passwords) may
       optionally be provided as well, in a pair of separate companion
       files with the .user-privileged suffix. The data should be stored
       in a regular file named after the user name, suffixed with
       .user-privileged, and a symlink pointing to it, named after the
       used numeric UID formatted in decimal with the same suffix. These
       companion files should not be readable to anyone but root.
       Example:

           -rw-r--r--. 1 root root  723 May 10 foobar.user
           -rw-------. 1 root root  123 May 10 foobar.user-privileged
           lrwxrwxrwx. 1 root root   19 May 10 4711.user -> foobar.user
           lrwxrwxrwx. 1 root root   19 May 10 4711.user-privileged -> foobar.user-privileged

       Similarly, group records following the format described in JSON
       Group Record[3] may be defined, using the file suffixes .group
       and .group-privileged.

       The primary user/group record files (i.e. those with the .user
       and .group suffixes) should not contain the "privileged" section
       as described in the specifications. The privileged user/group
       record files (i.e. those with the .user-privileged and
       .group-privileged suffixes) should contain this section,
       exclusively.

       Note that static user/group records generally do not override
       conflicting records in /etc/passwd or /etc/group or other account
       databases. In fact, before dropping in these files a reasonable
       level of care should be taken to avoid user/group name and
       UID/GID conflicts.

Конфигурация в /etc/nsswitch.conf (Configuration in /etc/nsswitch.conf)

Here is an example /etc/nsswitch.conf file that enables nss-systemd 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 SYSTEMD-MACHINED.SERVICE

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 ? /usr/lib/systemd/systemd vu-rawhide-0 731 ? /usr/lib/systemd/systemd-journald vu-rawhide-192 734 ? /usr/lib/systemd/systemd-networkd vu-rawhide-193 738 ? /usr/lib/systemd/systemd-resolved vu-rawhide-0 742 ? /usr/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 ? /usr/lib/systemd/systemd --user vu-rawhide-0 753 ? (sd-pam) vu-rawhide-0 1628 ? login -- zbyszek vu-rawhide-1000 1630 ? /usr/lib/systemd/systemd --user vu-rawhide-1000 1631 ? (sd-pam) vu-rawhide-1000 1637 pts/8 -zsh

Смотри также (See also)

systemd(1), systemd.exec(5), nss-resolve(8), nss-myhostname(8),
       nss-mymachines(8), systemd-userdbd.service(8),
       systemd-homed.service(8), systemd-machined.service(8),
       nsswitch.conf(5), getent(1)

Примечание (Note)

1. User/Group Record Lookup API via Varlink https://systemd.io/USER_GROUP_API

2. JSON User Records https://systemd.io/USER_RECORD

3. JSON Group Record https://systemd.io/GROUP_RECORD

Исходный текст на man7.org

libnss_systemd.so.2 ( 8 )