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'\" t
.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" Modified Sat Jul 24 18:16:02 1993 by Rik Faith (faith@cs.unc.edu)
.TH sleep 3 (date) "Linux man-pages (unreleased)"
.SH NAME
sleep \- sleep for a specified number of seconds
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.PP
.BI "unsigned int sleep(unsigned int " "seconds" );
.fi
.SH DESCRIPTION
.BR sleep ()
causes the calling thread to sleep either until
the number of real-time seconds specified in
.I seconds
have elapsed or until a signal arrives which is not ignored.
.SH RETURN VALUE
Zero if the requested time has elapsed,
or the number of seconds left to sleep,
if the call was interrupted by a signal handler.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR sleep ()
T} Thread safety MT-Unsafe sig:SIGCHLD/linux
.TE
.sp 1
.SH VERSIONS
On Linux,
.BR sleep ()
is implemented via
.BR nanosleep (2).
See the
.BR nanosleep (2)
man page for a discussion of the clock used.
.PP
On some systems,
.BR sleep ()
may be implemented using
.BR alarm (2)
and
.B SIGALRM
(POSIX.1 permits this);
mixing calls to
.BR alarm (2)
and
.BR sleep ()
is a bad idea.
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
POSIX.1-2001.
.SH CAVEATS
Using
.BR longjmp (3)
from a signal handler or modifying the handling of
.B SIGALRM
while sleeping will cause undefined results.
.SH SEE ALSO
.BR sleep (1),
.BR alarm (2),
.BR nanosleep (2),
.BR signal (2),
.BR signal (7)
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