alarm(2) — Linux manual page


alarm(2)                   System Calls Manual                  alarm(2)

NAME         top

       alarm - set an alarm clock for delivery of a signal

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <unistd.h>

       unsigned int alarm(unsigned int seconds);

DESCRIPTION         top

       alarm() arranges for a SIGALRM signal to be delivered to the
       calling process in seconds seconds.

       If seconds is zero, any pending alarm is canceled.

       In any event any previously set alarm() is canceled.

RETURN VALUE         top

       alarm() returns the number of seconds remaining until any
       previously scheduled alarm was due to be delivered, or zero if
       there was no previously scheduled alarm.

STANDARDS         top


HISTORY         top

       POSIX.1-2001, SVr4, 4.3BSD.

NOTES         top

       alarm() and setitimer(2) share the same timer; calls to one will
       interfere with use of the other.

       Alarms created by alarm() are preserved across execve(2) and are
       not inherited by children created via fork(2).

       sleep(3) may be implemented using SIGALRM; mixing calls to
       alarm() and sleep(3) is a bad idea.

       Scheduling delays can, as ever, cause the execution of the
       process to be delayed by an arbitrary amount of time.

SEE ALSO         top

       gettimeofday(2), pause(2), select(2), setitimer(2), sigaction(2),
       signal(2), timer_create(2), timerfd_create(2), sleep(3), time(7)

COLOPHON         top

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Linux man-pages 6.9.1          2024-05-02                       alarm(2)

Pages that refer to this page: tload(1)fork(2)getitimer(2)seccomp(2)signal(2)syscalls(2)sleep(3)ualarm(3)usleep(3)systemd.exec(5)signal(7)signal-safety(7)time(7)