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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | NOTES | SEE ALSO | NOTES | COLOPHON |
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SD_LOGIN_MONITOR_NEW(3) sd_login_monitor_new SD_LOGIN_MONITOR_NEW(3)
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
#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);
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_get_fd().
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
parameter.
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:
-EINVAL
An input parameter was invalid (out of range, or NULL, where that
is not accepted). The specified category to watch is not known.
-ENOMEM
Memory allocation failed.
The sd_login_monitor_new(), sd_login_monitor_unref(),
sd_login_monitor_flush(), sd_login_monitor_get_fd(),
sd_login_monitor_get_events() and sd_login_monitor_get_timeout()
interfaces are available as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
systemd(1), sd-login(3), sd_get_seats(3), poll(2), clock_gettime(2)
1. Clean-up Variable Attribute
https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2018-02-02. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2018-02-02.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to man-pages@man7.org
systemd 234 SD_LOGIN_MONITOR_NEW(3)
Pages that refer to this page: sd-login(3), systemd.directives(7), systemd.index(7)
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