1alarm(2)                      System Calls Manual                     alarm(2)
2
3
4

NAME

6       alarm - set an alarm clock for delivery of a signal
7

LIBRARY

9       Standard C library (libc, -lc)
10

SYNOPSIS

12       #include <unistd.h>
13
14       unsigned int alarm(unsigned int seconds);
15

DESCRIPTION

17       alarm()  arranges  for  a SIGALRM signal to be delivered to the calling
18       process in seconds seconds.
19
20       If seconds is zero, any pending alarm is canceled.
21
22       In any event any previously set alarm() is canceled.
23

RETURN VALUE

25       alarm() returns the number of seconds remaining  until  any  previously
26       scheduled alarm was due to be delivered, or zero if there was no previ‐
27       ously scheduled alarm.
28

STANDARDS

30       POSIX.1-2008.
31

HISTORY

33       POSIX.1-2001, SVr4, 4.3BSD.
34

NOTES

36       alarm() and setitimer(2) share the same timer; calls to one will inter‐
37       fere with use of the other.
38
39       Alarms  created  by  alarm() are preserved across execve(2) and are not
40       inherited by children created via fork(2).
41
42       sleep(3) may be implemented using SIGALRM; mixing calls to alarm()  and
43       sleep(3) is a bad idea.
44
45       Scheduling  delays  can, as ever, cause the execution of the process to
46       be delayed by an arbitrary amount of time.
47

SEE ALSO

49       gettimeofday(2), pause(2), select(2), setitimer(2), sigaction(2),  sig‐
50       nal(2), timer_create(2), timerfd_create(2), sleep(3), time(7)
51
52
53
54Linux man-pages 6.05              2023-03-30                          alarm(2)