sd_get_seats, sd_get_sessions, sd_get_uids, sd_get_machine_names — Determine available seats, sessions, logged in users and virtual machines/containers
#include <systemd/sd-login.h>
| int sd_get_seats( | char*** seats ); | 
| int sd_get_sessions( | char*** sessions ); | 
| int sd_get_uids( | uid_t** users ); | 
| int sd_get_machine_names( | char*** machines ); | 
sd_get_seats() may be used
                to determine all currently available local
                seats. Returns a NULL terminated array of seat
                identifiers. The returned array and all strings it
                references need to be freed with the libc
                free(3)
                call after use. Note that instead of an empty array
                NULL may be returned and should be considered
                equivalent to an empty array.
Similar, sd_get_sessions() may
                be used to determine all current login sessions.
Similar, sd_get_uids() may
                be used to determine all Unix users who currently have login sessions.
Similar,
                sd_get_machine_names() may be
                used to determine all current virtual machines and
                containers on the system.
Note that the returned lists are not sorted and in an undefined order.
On success sd_get_seats(),
                sd_get_sessions(),
                sd_get_uids() and
                sd_get_machine_names() return the
                number of entries in the arrays. On failure, these
                calls return a negative errno-style error code.
The sd_get_seats(),
                sd_get_sessions(),
                sd_get_uids() and
                sd_get_machine_names() interfaces
                are available as shared library, which can be compiled
                and linked to with the
                libsystemd-login
                pkg-config(1)
                file.