NAME

       sd_seat_get_active, sd_seat_get_sessions, sd_seat_can_tty, sd_seat_can_graphical -
       Determine state of a specific seat

SYNOPSIS

       #include <systemd/sd-login.h>

       int sd_seat_get_active(const char *seat, char **session, uid_t *uid);

       int sd_seat_get_sessions(const char *seat, char ***ret_sessions, uid_t **ret_uids,
                                unsigned int *ret_n_uids);

       int sd_seat_can_tty(const char *seat);

       int sd_seat_can_graphical(const char *seat);

DESCRIPTION

       sd_seat_get_active() may be used to determine which session is currently active on a seat,
       if there is any. Returns the session identifier and the user identifier of the Unix user
       the session is belonging to. Either the session or the user identifier parameter can be
       passed NULL, in case only one of the parameters shall be queried. The returned string
       needs to be freed with the libc free(3) call after use.

       sd_seat_get_sessions() may be used to determine all sessions on the specified seat.
       Returns two arrays, one (NULL terminated) with the session identifiers of the sessions and
       one with the user identifiers of the Unix users the sessions belong to. An additional
       parameter may be used to return the number of entries in the latter array. This value is
       the same as the return value if the return value is nonnegative. The output parameters may
       be passed as NULL in case these output values are not needed. The arrays and the strings
       referenced by them 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.

       sd_seat_can_tty() may be used to determine whether a specific seat provides TTY
       functionality, i.e. is useful as a text console.

       sd_seat_can_graphical() may be used to determine whether a specific seat provides graphics
       functionality, i.e. is useful as a graphics display.

       If the seat parameter of any of these functions is passed as NULL, the operation is
       executed for the seat of the session of the calling process, if there is any.

RETURN VALUE

       On success, sd_seat_get_active() returns 0 or a positive integer. On success,
       sd_seat_get_sessions() returns the number of entries in the session identifier array. If
       the test succeeds, sd_seat_can_tty() and sd_seat_can_graphical() return a positive
       integer, if it fails 0. On failure, these calls return a negative errno-style error code.

   Errors
       Returned errors may indicate the following problems:

       -ENODATA
           The given field is not specified for the described seat.

       -ENXIO
           The specified seat is unknown.

       -EINVAL
           An input parameter was invalid (out of range, or NULL, where that is not accepted).

       -ENOMEM
           Memory allocation failed.

NOTES

       Functions described here are available as a shared library, which can be compiled against
       and linked to with the libsystemd pkg-config(1) file.

       The code described here uses getenv(3), which is declared to be not multi-thread-safe.
       This means that the code calling the functions described here must not call setenv(3) from
       a parallel thread. It is recommended to only do calls to setenv() from an early phase of
       the program when no other threads have been started.

HISTORY

       sd_seat_can_tty() and sd_seat_can_graphical() were added in version 186.

SEE ALSO

       systemd(1), sd-login(3), sd_session_get_seat(3)