'\" t
.TH "SD_SEAT_GET_ACTIVE" "3" "" "systemd 256.7" "sd_seat_get_active"
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.SH "NAME"
sd_seat_get_active, sd_seat_get_sessions, sd_seat_can_tty, sd_seat_can_graphical \- Determine state of a specific seat
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-login\&.h>
.fi
.ft
.HP \w'int\ sd_seat_get_active('u
.BI "int sd_seat_get_active(const\ char\ *" "seat" ", char\ **" "session" ", uid_t\ *" "uid" ");"
.HP \w'int\ sd_seat_get_sessions('u
.BI "int sd_seat_get_sessions(const\ char\ *" "seat" ", char\ ***" "ret_sessions" ", uid_t\ **" "ret_uids" ", unsigned\ int\ *" "ret_n_uids" ");"
.HP \w'int\ sd_seat_can_tty('u
.BI "int sd_seat_can_tty(const\ char\ *" "seat" ");"
.HP \w'int\ sd_seat_can_graphical('u
.BI "int sd_seat_can_graphical(const\ char\ *" "seat" ");"
.SH "DESCRIPTION"
.PP
\fBsd_seat_get_active()\fR
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
\fBNULL\fR, in case only one of the parameters shall be queried\&. The returned string needs to be freed with the libc
\fBfree\fR(3)
call after use\&.
.PP
\fBsd_seat_get_sessions()\fR
may be used to determine all sessions on the specified seat\&. Returns two arrays, one (\fBNULL\fR
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
\fBNULL\fR
in case these output values are not needed\&. The arrays and the strings referenced by them need to be freed with the libc
\fBfree\fR(3)
call after use\&. Note that instead of an empty array
\fBNULL\fR
may be returned and should be considered equivalent to an empty array\&.
.PP
\fBsd_seat_can_tty()\fR
may be used to determine whether a specific seat provides TTY functionality, i\&.e\&. is useful as a text console\&.
.PP
\fBsd_seat_can_graphical()\fR
may be used to determine whether a specific seat provides graphics functionality, i\&.e\&. is useful as a graphics display\&.
.PP
If the
\fIseat\fR
parameter of any of these functions is passed as
\fBNULL\fR, the operation is executed for the seat of the session of the calling process, if there is any\&.
.SH "RETURN VALUE"
.PP
On success,
\fBsd_seat_get_active()\fR
returns 0 or a positive integer\&. On success,
\fBsd_seat_get_sessions()\fR
returns the number of entries in the session identifier array\&. If the test succeeds,
\fBsd_seat_can_tty()\fR
and
\fBsd_seat_can_graphical()\fR
return a positive integer, if it fails 0\&. On failure, these calls return a negative errno\-style error code\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-ENODATA\fR
.RS 4
The given field is not specified for the described seat\&.
.RE
.PP
\fB\-ENXIO\fR
.RS 4
The specified seat is unknown\&.
.RE
.PP
\fB\-EINVAL\fR
.RS 4
An input parameter was invalid (out of range, or
\fBNULL\fR, where that is not accepted)\&.
.RE
.PP
\fB\-ENOMEM\fR
.RS 4
Memory allocation failed\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "HISTORY"
.PP
\fBsd_seat_can_tty()\fR
and
\fBsd_seat_can_graphical()\fR
were added in version 186\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-login\fR(3), \fBsd_session_get_seat\fR(3)