NAME

       sd_uid_get_state, sd_uid_is_on_seat, sd_uid_get_sessions, sd_uid_get_seats, sd_uid_get_display -
       Determine login state of a specific Unix user ID

SYNOPSIS

       #include <systemd/sd-login.h>

       int sd_uid_get_state(uid_t uid, char **state);

       int sd_uid_is_on_seat(uid_t uid, int require_active, const char *seat);

       int sd_uid_get_sessions(uid_t uid, int require_active, char ***sessions);

       int sd_uid_get_seats(uid_t uid, int require_active, char ***seats);

       int sd_uid_get_display(uid_t uid, char **session);

DESCRIPTION

       sd_uid_get_state() may be used to determine the login state of a specific Unix user identifier. The
       following states are currently known: "offline" (user not logged in at all), "lingering" (user not logged
       in, but some user services running), "online" (user logged in, but not active, i.e. has no session in the
       foreground), "active" (user logged in, and has at least one active session, i.e. one session in the
       foreground), "closing" (user not logged in, and not lingering, but some processes are still around). In
       the future additional states might be defined, client code should be written to be robust in regards to
       additional state strings being returned. The returned string needs to be freed with the libc free(3) call
       after use.

       sd_uid_is_on_seat() may be used to determine whether a specific user is logged in or active on a specific
       seat. Accepts a Unix user identifier and a seat identifier string as parameters. The require_active
       parameter is a boolean value. If non-zero (true), this function will test if the user is active (i.e. has
       a session that is in the foreground and accepting user input) on the specified seat, otherwise (false)
       only if the user is logged in (and possibly inactive) on the specified seat.

       sd_uid_get_sessions() may be used to determine the current sessions of the specified user. Accepts a Unix
       user identifier as parameter. The require_active parameter controls whether the returned list shall
       consist of only those sessions where the user is currently active (> 0), where the user is currently
       online but possibly inactive (= 0), or logged in but possibly closing the session (< 0). The call returns
       a NULL terminated string array of session identifiers in sessions which needs to be freed by the caller
       with the libc free(3) call after use, including all the strings referenced. If the string array parameter
       is passed as NULL, the array will not be filled in, but the return code still indicates the number of
       current sessions. Note that instead of an empty array NULL may be returned and should be considered
       equivalent to an empty array.

       Similarly, sd_uid_get_seats() may be used to determine the list of seats on which the user currently has
       sessions. Similar semantics apply, however note that the user may have multiple sessions on the same seat
       as well as sessions with no attached seat and hence the number of entries in the returned array may
       differ from the one returned by sd_uid_get_sessions().

       sd_uid_get_display() returns the name of the "primary" session of a user. If the user has graphical
       sessions, it will be the oldest graphical session. Otherwise, it will be the oldest open session.

RETURN VALUE

       On success, sd_uid_get_state() returns 0 or a positive integer. If the test succeeds, sd_uid_is_on_seat()
       returns a positive integer; if it fails, 0.  sd_uid_get_sessions() and sd_uid_get_seats() return the
       number of entries in the returned arrays.  sd_uid_get_display() returns a non-negative code on success.
       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 user.

       -ENXIO
           The specified seat is unknown.

       -EINVAL
           An input parameter was invalid (out of range, or NULL, where that is not accepted). This is also
           returned if the passed user ID is 0xFFFF or 0xFFFFFFFF, which are undefined on Linux.

       -ENOMEM
           Memory allocation failed.

NOTES

       These APIs are implemented as a shared library, which can be compiled and linked to with the
       libsystemd pkg-config(1) file.

SEE ALSO

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