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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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ualarm(3) Library Functions Manual ualarm(3)
ualarm - schedule signal after given number of microseconds
Standard C library (libc, -lc)
#include <unistd.h>
useconds_t ualarm(useconds_t usecs, useconds_t interval);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
ualarm():
Since glibc 2.12:
(_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
|| /* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE >= 500
The ualarm() function causes the signal SIGALRM to be sent to the
invoking process after (not less than) usecs microseconds. The
delay may be lengthened slightly by any system activity or by the
time spent processing the call or by the granularity of system
timers.
Unless caught or ignored, the SIGALRM signal will terminate the
process.
If the interval argument is nonzero, further SIGALRM signals will
be sent every interval microseconds after the first.
This function returns the number of microseconds remaining for any
alarm that was previously set, or 0 if no alarm was pending.
EINTR Interrupted by a signal; see signal(7).
EINVAL usecs or interval is not smaller than 1000000. (On systems
where that is considered an error.)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ ualarm() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
None.
4.3BSD, POSIX.1-2001. POSIX.1-2001 marks it as obsolete. Removed
in POSIX.1-2008.
4.3BSD, SUSv2, and POSIX do not define any errors.
POSIX.1-2001 does not specify what happens if the usecs argument
is 0. On Linux (and probably most other systems), the effect is
to cancel any pending alarm.
The type useconds_t is an unsigned integer type capable of holding
integers in the range [0,1000000]. On the original BSD
implementation, and in glibc before glibc 2.1, the arguments to
ualarm() were instead typed as unsigned int. Programs will be
more portable if they never mention useconds_t explicitly.
The interaction of this function with other timer functions such
as alarm(2), sleep(3), nanosleep(2), setitimer(2),
timer_create(2), timer_delete(2), timer_getoverrun(2),
timer_gettime(2), timer_settime(2), usleep(3) is unspecified.
This function is obsolete. Use setitimer(2) or POSIX interval
timers (timer_create(2), etc.) instead.
alarm(2), getitimer(2), nanosleep(2), select(2), setitimer(2),
usleep(3), time(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 ualarm(3)
Pages that refer to this page: usleep(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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