userdbctl

systemd
userdbctl 1
userdbctl Inspect users, groups and group memberships
`userdbctl` OPTIONS COMMAND NAME

## Description

`userdbctl` may be used to inspect user and groups (as well as group memberships) of the system. This client utility inquires user/group information provided by various system services, both operating on JSON user/group records (as defined by the JSON User Record and JSON Group Record definitions), and classic UNIX NSS/glibc user and group records. This tool is primarily a client to the User/Group Record Lookup API via Varlink.

## Options

The following options are understood:

`--output=`MODE

  Choose the output mode, takes one of `classic`, `friendly`, `table`, `json`. If `classic`, an output very close to the format of `/etc/passwd` or `/etc/group` is generated. If `friendly` a more comprehensive and user friendly, human readable output is generated; if `table` a minimal, tabular output is generated; if `json` a JSON formatted output is generated. Defaults to `friendly` if a user/group is specified on the command line, `table` otherwise.

`--service=`SERVICE:SERVICE…
`-s` SERVICE:SERVICE…

  Controls which services to query for users/groups. Takes a list of one or more service names, separated by `:`. See below for a list of well-known service names. If not specified all available services are queried at once.

`--with-nss=`BOOL

  Controls whether to include classic glibc/NSS user/group lookups in the output. If `--with-nss=no` is used any attempts to resolve or enumerate users/groups provided only via glibc NSS is suppressed. If `--with-nss=yes` is specified such users/groups are included in the output (which is the default).

`--synthesize=`BOOL

  Controls whether to synthesize records for the root and nobody users/groups if they aren't defined otherwise. By default (or `yes`) such records are implicitly synthesized if otherwise missing since they have special significance to the OS. When `no` this synthesizing is turned off.

`-N`

  This option is short for `--with-nss=no` `--synthesize=no`. Use this option to show only records that are natively defined as JSON user or group records, with all NSS/glibc compatibility and all implicit synthesis turned off.

## Commands

The following commands are understood:

`user` USER…

  List all known users records or show details of one or more specified user records. Use `--output=` to tweak output mode.

`group` GROUP…

  List all known group records or show details of one or more specified group records. Use `--output=` to tweak output mode.

`users-in-group` GROUP…

  List users that are members of the specified groups. If no groups are specified list all user/group memberships defined. Use `--output=` to tweak output mode.

`groups-of-user` USER…

  List groups that the specified users are members of. If no users are specified list all user/group memberships defined (in this case `groups-of-user` and `users-in-group` are equivalent). Use `--output=` to tweak output mode.

`services`

  List all services currently providing user/group definitions to the system. See below for a list of well-known services providing user information.

`ssh-authorized-keys`

  This operation is not a public, user-facing interface. It is used to allow the SSH daemon to pick up authorized keys from user records, see below.

## Well-Known Services

The `userdbctl services` command will list all currently running services that provide user or group definitions to the system. The following are well-known services are shown among this list.

`io.systemd.DynamicUser`

  This service is provided by the system service manager itself (i.e. PID 1) and makes all users (and their groups) synthesized through the `DynamicUser=` setting in service unit files available to the system (see systemd.exec 5 for details about this setting).

`io.systemd.Home`

  This service is provided by systemd-homed.service 8 and makes all users (and their groups) belonging to home directories managed by that service available to the system.

`io.systemd.Multiplexer`

  This service is provided by systemd-userdbd.service 8 and multiplexes user/group look-ups to all other running lookup services. This is the primary entry point for user/group record clients, as it simplifies client side implementation substantially since they can ask a single service for lookups instead of asking all running services in parallel. `userdbctl` uses this service preferably, too, unless `--with-nss=` or `--service=` are used, in which case finer control over the services to talk to is required.

`io.systemd.NameSeviceSwitch`

  This service is (also) provided by systemd-userdbd.service 8 and converts classic NSS/glibc user and group records to JSON user/group records, providing full backwards compatibility. Use `--with-nss=no` to disable this compatibility, see above. Note that compatibility is actually provided in both directions: nss-systemd 8 will automatically synthesize classic NSS/glibc user/group records from all JSON user/group records provided to the system, thus using both APIs is mostly equivalent and provides access to the same data, however the NSS/glibc APIs necessarily expose a more reduced set of fields only.

Note that `userdbctl` has internal support for NSS-based lookups too. This means that if neither `io.systemd.Multiplexer` nor `io.systemd.NameSeviceSwitch` are running look-ups into the the basic user/group databases will still work.

## Integration with SSH

The `userdbctl` tool may be used to make the list of SSH authorized keys possibly contained in a user record available to the SSH daemon for authentication. For that configure the following in sshd_config 5:

    …
    AuthorizedKeysCommand /usr/bin/userdbctl ssh-authorized-keys %u
    AuthorizedKeysCommandUser root
    …

## Exit status

On success, 0 is returned, a non-zero failure code otherwise.

## See Also

systemd 1, systemd-userdbd.service 8, systemd-homed.service 8, nss-systemd 8, getent 1