2. System calls (functions provided by the kernel)
ALARMSection: Linux Programmer's Manual (2)
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NAMEalarm - set an alarm clock for delivery of a signal
#include <unistd.h> unsigned int alarm(unsigned int seconds);
DESCRIPTIONalarm() 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 VALUEalarm() 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.
CONFORMING TOPOSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
NOTESalarm() 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 ALSOgettimeofday(2), pause(2), select(2), setitimer(2), sigaction(2), signal(2), timer_create(2), timerfd_create(2), sleep(3), time(7)
COLOPHONThis page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
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