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.Dd $Mdocdate: December 7 2021 $ .Dt SLEEP 3 .Os .Sh NAME .Nm sleep .Nd suspend execution for an interval of seconds .Sh SYNOPSIS n unistd.h .Ft unsigned int .Fn sleep "unsigned int seconds" .Sh DESCRIPTION The .Fn sleep function suspends execution of the calling thread until at least the given number of .Fa seconds have elapsed or an unmasked signal is delivered to the calling thread.
p This version of .Fn sleep is implemented with .Xr nanosleep 2 , so delivery of any unmasked signal will terminate the sleep early, even if .Dv SA_RESTART is set with .Xr sigaction 2 for the interrupting signal. .Sh RETURN VALUES If .Fn sleep sleeps for the full count of .Fa seconds , it returns 0. Otherwise, .Fn sleep returns the number of seconds remaining from the original request. .Sh ERRORS The .Fn sleep function sets .Va errno to .Dv EINTR if it is interrupted by the delivery of a signal. .Sh SEE ALSO .Xr sleep 1 , .Xr nanosleep 2 , .Xr sigaction 2 .Sh STANDARDS The .Fn sleep function conforms to .St -p1003.1-2008 .
p Setting .Va errno is an extension to that specification. .Sh HISTORY A .Fn sleep system call first appeared in .At v2 . In .At v7 , it was removed and replaced by a C library implementation based on .Xr signal 3 and .Xr alarm 3 . For .Ox 2.1 , it was reimplemented as a wrapper around the .Xr nanosleep 2 system call.