1SD_LOGIN_MONITOR_NEW(3)      sd_login_monitor_new      SD_LOGIN_MONITOR_NEW(3)
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NAME

6       sd_login_monitor_new, sd_login_monitor_unref, sd_login_monitor_unrefp,
7       sd_login_monitor_flush, sd_login_monitor_get_fd,
8       sd_login_monitor_get_events, sd_login_monitor_get_timeout,
9       sd_login_monitor - Monitor login sessions, seats, users and virtual
10       machines/containers
11

SYNOPSIS

13       #include <systemd/sd-login.h>
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15       int sd_login_monitor_new(const char *category, sd_login_monitor **ret);
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17       sd_login_monitor *sd_login_monitor_unref(sd_login_monitor *m);
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19       void sd_login_monitor_unrefp(sd_login_monitor **m);
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21       int sd_login_monitor_flush(sd_login_monitor *m);
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23       int sd_login_monitor_get_fd(sd_login_monitor *m);
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25       int sd_login_monitor_get_events(sd_login_monitor *m);
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27       int sd_login_monitor_get_timeout(sd_login_monitor *m,
28                                        uint64_t *timeout_usec);
29

DESCRIPTION

31       sd_login_monitor_new() may be used to monitor login sessions, users,
32       seats, and virtual machines/containers. Via a monitor object a file
33       descriptor can be integrated into an application defined event loop
34       which is woken up each time a user logs in, logs out or a seat is added
35       or removed, or a session, user, seat or virtual machine/container
36       changes state otherwise. The first parameter takes a string which can
37       be "seat" (to get only notifications about seats being added, removed
38       or changed), "session" (to get only notifications about sessions being
39       created or removed or changed), "uid" (to get only notifications when a
40       user changes state in respect to logins) or "machine" (to get only
41       notifications when a virtual machine or container is started or
42       stopped). If notifications shall be generated in all these conditions,
43       NULL may be passed. Note that in the future additional categories may
44       be defined. The second parameter returns a monitor object and needs to
45       be freed with the sd_login_monitor_unref() call after use.
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47       sd_login_monitor_unref() may be used to destroy a monitor object. Note
48       that this will invalidate any file descriptor returned by
49       sd_login_monitor_get_fd().
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51       sd_login_monitor_unrefp() is similar to sd_login_monitor_unref() but
52       takes a pointer to a pointer to an sd_login_monitor object. This call
53       is useful in conjunction with GCC's and LLVM's Clean-up Variable
54       Attribute[1]. Note that this function is defined as inline function.
55       Use a declaration like the following, in order to allocate a login
56       monitor object that is freed automatically as the code block is left:
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58           {
59             __attribute__((cleanup(sd_login_monitor_unrefp))) sd_login_monitor *m = NULL;
60             int r;
61             ...
62             r = sd_login_monitor_new(NULL, &m);
63             if (r < 0) {
64               errno = -r;
65               fprintf(stderr, "Failed to allocate login monitor object: %m\n");
66             }
67             ...
68           }
69
70       sd_login_monitor_flush() may be used to reset the wakeup state of the
71       monitor object. Whenever an event causes the monitor to wake up the
72       event loop via the file descriptor this function needs to be called to
73       reset the wake-up state. If this call is not invoked, the file
74       descriptor will immediately wake up the event loop again.
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76       sd_login_monitor_unref() and sd_login_monitor_unrefp() execute no
77       operation if the passed in monitor object is NULL.
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79       sd_login_monitor_get_fd() may be used to retrieve the file descriptor
80       of the monitor object that may be integrated in an application defined
81       event loop, based around poll(2) or a similar interface. The
82       application should include the returned file descriptor as wake-up
83       source for the events mask returned by sd_login_monitor_get_events().
84       It should pass a timeout value as returned by
85       sd_login_monitor_get_timeout(). Whenever a wake-up is triggered the
86       file descriptor needs to be reset via sd_login_monitor_flush(). An
87       application needs to reread the login state with a function like
88       sd_get_seats(3) or similar to determine what changed.
89
90       sd_login_monitor_get_events() will return the poll() mask to wait for.
91       This function will return a combination of POLLIN, POLLOUT and similar
92       to fill into the ".events" field of struct pollfd.
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94       sd_login_monitor_get_timeout() will return a timeout value for usage in
95       poll(). This returns a value in microseconds since the epoch of
96       CLOCK_MONOTONIC for timing out poll() in timeout_usec. See
97       clock_gettime(2) for details about CLOCK_MONOTONIC. If there is no
98       timeout to wait for this will fill in (uint64_t) -1 instead. Note that
99       poll() takes a relative timeout in milliseconds rather than an absolute
100       timeout in microseconds. To convert the absolute 'µs' timeout into
101       relative 'ms', use code like the following:
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103           uint64_t t;
104           int msec;
105           sd_login_monitor_get_timeout(m, &t);
106           if (t == (uint64_t) -1)
107             msec = -1;
108           else {
109             struct timespec ts;
110             uint64_t n;
111             clock_gettime(CLOCK_MONOTONIC, &ts);
112             n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
113             msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
114           }
115
116       The code above does not do any error checking for brevity's sake. The
117       calculated msec integer can be passed directly as poll()'s timeout
118       parameter.
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RETURN VALUE

121       On success, sd_login_monitor_new(), sd_login_monitor_flush() and
122       sd_login_monitor_get_timeout() return 0 or a positive integer. On
123       success, sd_login_monitor_get_fd() returns a Unix file descriptor. On
124       success, sd_login_monitor_get_events() returns a combination of POLLIN,
125       POLLOUT and suchlike. On failure, these calls return a negative
126       errno-style error code.
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128       sd_login_monitor_unref() always returns NULL.
129
130   Errors
131       Returned errors may indicate the following problems:
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133       -EINVAL
134           An input parameter was invalid (out of range, or NULL, where that
135           is not accepted). The specified category to watch is not known.
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137       -ENOMEM
138           Memory allocation failed.
139

NOTES

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

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

148        1. Clean-up Variable Attribute
149           https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
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153systemd 253                                            SD_LOGIN_MONITOR_NEW(3)
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