alarm(2)                                                           alarm(2)




 NAME    [Toc]    [Back]
      alarm - set a process's alarm clock

 SYNOPSIS    [Toc]    [Back]
      #include <unistd.h>

      unsigned int alarm(unsigned int sec);

 DESCRIPTION    [Toc]    [Back]
      alarm() instructs the alarm clock of the calling process to send the
      signal SIGALRM to the calling process after the number of real-time
      seconds specified by sec have elapsed; see signal(5).  Specific
      implementations might place limitations on the maximum supported alarm
      time.  The constant MAX_ALARM defined in <sys/param.h> specifies the
      implementation-specific maximum.  Whenever sec is greater that this
      maximum, it is silently rounded down to it.  On all implementations,
      MAX_ALARM is guaranteed to be at least 31 days (in seconds).

      Alarm requests are not stacked; successive calls reset the alarm clock
      of the calling process.

      If sec is 0, any previously made alarm request is canceled.

      Alarms are not inherited by a child process across a fork(), but are
      inherited across an exec().

      On systems that support the getitimer() and setitimer() system calls,
      the timer mechanism used by alarm() is the same as that used by
      ITIMER_REAL.  Thus successive calls to alarm(), getitimer(), and
      setitimer() set and return the state of a single timer.  In addition,
      alarm() sets the timer interval to zero.

 RETURN VALUE    [Toc]    [Back]
      alarm() returns the amount of time previously remaining in the alarm
      clock of the calling process.

 WARNINGS    [Toc]    [Back]
      In some implementations, error bounds for alarm are -1, +0 seconds
      (for the posting of the alarm, not the restart of the process).  Thus
      a delay of 1 second can return immediately.  The setitimer() routine
      can be used to create a more precise delay.

 SEE ALSO    [Toc]    [Back]
      sleep(1), exec(2), getitimer(2), pause(2), signal(5), sleep(3C).

 STANDARDS CONFORMANCE    [Toc]    [Back]
      alarm(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1


 Hewlett-Packard Company            - 1 -   HP-UX 11i Version 2: August 2003