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)