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
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 at all 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.
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.
Returned errors may indicate the following problems:
The given field is not specified for the described user.
The specified seat is unknown.
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.
Memory allocation failed.
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systemd 233 SD_UID_GET_STATE(3)