ALARM(2) System Calls ALARM(2)
NAME
alarm - schedule an alarm signal
SYNOPSIS
#include <unistd.h>
unsigned int alarm(
unsigned int seconds);
DESCRIPTION
The
alarm() function causes the system to generate a
SIGALRM signal
for the process after the number of real-time seconds specified by
seconds have elapsed (see
signal.h(3HEAD)). Processor scheduling
delays may prevent the process from handling the signal as soon as it
is generated.
If
seconds is 0, a pending alarm request, if any, is cancelled. If
seconds is greater than
LONG_MAX/
hz,
seconds is rounded down to
LONG_MAX/
hz. The value of
hz is normally 100.
Alarm requests are not stacked; only one
SIGALRM generation can be
scheduled in this manner; if the
SIGALRM signal has not yet been
generated, the call will result in rescheduling the time at which the
SIGALRM signal will be generated.
The
fork(2) function clears pending alarms in the child process. A
new process image created by one of the
exec(2) functions inherits
the time left to an alarm signal in the old process's image.
RETURN VALUES
If there is a previous alarm request with time remaining,
alarm() returns a non-zero value that is the number of seconds until the
previous request would have generated a
SIGALRM signal.
Otherwise,
alarm() returns 0.
ERRORS
The
alarm() function is always successful; no return value is
reserved to indicate an error.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Standard |
+--------------------+-------------------+
|MT-Level | Async-Signal-Safe |
+--------------------+-------------------+
SEE ALSO
exec(2),
fork(2),
signal.h(3HEAD),
attributes(7),
standards(7) June 6, 2007 ALARM(2)
