sd_login_monitor_get_events(3) — Linux manual page


SD_LOGIN_MONITOR_NEW(3)     sd_login_monitor_new     SD_LOGIN_MONITOR_NEW(3)

NAME         top

       sd_login_monitor_new, sd_login_monitor_unref,
       sd_login_monitor_unrefp, sd_login_monitor_flush,
       sd_login_monitor_get_fd, sd_login_monitor_get_events,
       sd_login_monitor_get_timeout, sd_login_monitor - Monitor login
       sessions, seats, users and virtual machines/containers

SYNOPSIS         top

       #include <systemd/sd-login.h>

       int sd_login_monitor_new(const char *category,
                                sd_login_monitor **ret);

       sd_login_monitor *sd_login_monitor_unref(sd_login_monitor *m);

       void sd_login_monitor_unrefp(sd_login_monitor **m);

       int sd_login_monitor_flush(sd_login_monitor *m);

       int sd_login_monitor_get_fd(sd_login_monitor *m);

       int sd_login_monitor_get_events(sd_login_monitor *m);

       int sd_login_monitor_get_timeout(sd_login_monitor *m,
                                        uint64_t *timeout_usec);

DESCRIPTION         top

       sd_login_monitor_new() may be used to monitor login sessions, users,
       seats, and virtual machines/containers. Via a monitor object a file
       descriptor can be integrated into an application defined event loop
       which is woken up each time a user logs in, logs out or a seat is
       added or removed, or a session, user, seat or virtual
       machine/container changes state otherwise. The first parameter takes
       a string which can be "seat" (to get only notifications about seats
       being added, removed or changed), "session" (to get only
       notifications about sessions being created or removed or changed),
       "uid" (to get only notifications when a user changes state in respect
       to logins) or "machine" (to get only notifications when a virtual
       machine or container is started or stopped). If notifications shall
       be generated in all these conditions, NULL may be passed. Note that
       in the future additional categories may be defined. The second
       parameter returns a monitor object and needs to be freed with the
       sd_login_monitor_unref() call after use.

       sd_login_monitor_unref() may be used to destroy a monitor object.
       Note that this will invalidate any file descriptor returned by

       sd_login_monitor_unrefp() is similar to sd_login_monitor_unref() but
       takes a pointer to a pointer to an sd_login_monitor object. This call
       is useful in conjunction with GCC's and LLVM's Clean-up Variable
       Attribute[1]. Note that this function is defined as inline function.
       Use a declaration like the following, in order to allocate a login
       monitor object that is freed automatically as the code block is left:

             __attribute__((cleanup(sd_login_monitor_unrefp))) sd_login_monitor *m = NULL;
             int r;
             r = sd_login_monitor_default(&m);
             if (r < 0)
               fprintf(stderr, "Failed to allocate login monitor object: %s\n", strerror(-r));

       sd_login_monitor_flush() may be used to reset the wakeup state of the
       monitor object. Whenever an event causes the monitor to wake up the
       event loop via the file descriptor this function needs to be called
       to reset the wake-up state. If this call is not invoked, the file
       descriptor will immediately wake up the event loop again.

       sd_login_monitor_unref() and sd_login_monitor_unrefp() execute no
       operation if the passed in monitor object is NULL.

       sd_login_monitor_get_fd() may be used to retrieve the file descriptor
       of the monitor object that may be integrated in an application
       defined event loop, based around poll(2) or a similar interface. The
       application should include the returned file descriptor as wake-up
       source for the events mask returned by sd_login_monitor_get_events().
       It should pass a timeout value as returned by
       sd_login_monitor_get_timeout(). Whenever a wake-up is triggered the
       file descriptor needs to be reset via sd_login_monitor_flush(). An
       application needs to reread the login state with a function like
       sd_get_seats(3) or similar to determine what changed.

       sd_login_monitor_get_events() will return the poll() mask to wait
       for. This function will return a combination of POLLIN, POLLOUT and
       similar to fill into the ".events" field of struct pollfd.

       sd_login_monitor_get_timeout() will return a timeout value for usage
       in poll(). This returns a value in microseconds since the epoch of
       CLOCK_MONOTONIC for timing out poll() in timeout_usec. See
       clock_gettime(2) for details about CLOCK_MONOTONIC. If there is no
       timeout to wait for this will fill in (uint64_t) -1 instead. Note
       that poll() takes a relative timeout in milliseconds rather than an
       absolute timeout in microseconds. To convert the absolute 'µs'
       timeout into relative 'ms', use code like the following:

           uint64_t t;
           int msec;
           sd_login_monitor_get_timeout(m, &t);
           if (t == (uint64_t) -1)
             msec = -1;
           else {
             struct timespec ts;
             uint64_t n;
             clock_gettime(CLOCK_MONOTONIC, &ts);
             n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
             msec = t > n ? (int) ((t - n + 999) / 1000) : 0;

       The code above does not do any error checking for brevity's sake. The
       calculated msec integer can be passed directly as poll()'s timeout

RETURN VALUE         top

       On success, sd_login_monitor_new(), sd_login_monitor_flush() and
       sd_login_monitor_get_timeout() return 0 or a positive integer. On
       success, sd_login_monitor_get_fd() returns a Unix file descriptor. On
       success, sd_login_monitor_get_events() returns a combination of
       POLLIN, POLLOUT and suchlike. On failure, these calls return a
       negative errno-style error code.

       sd_login_monitor_unref() always returns NULL.

       Returned errors may indicate the following problems:

           An input parameter was invalid (out of range, or NULL, where that
           is not accepted). The specified category to watch is not known.

           Memory allocation failed.

NOTES         top

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

SEE ALSO         top

       systemd(1), sd-login(3), sd_get_seats(3), poll(2), clock_gettime(2)

NOTES         top

        1. Clean-up Variable Attribute

COLOPHON         top

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systemd 246                                          SD_LOGIN_MONITOR_NEW(3)

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