'\" t .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" .\" References consulted: .\" Linux libc source code .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) .\" 386BSD man pages .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu) .\" Modified 2001-04-01 by aeb .\" Modified 2003-07-23 by aeb .\" .TH usleep 3 2024-05-02 "Linux man-pages 6.9.1" .SH NAME usleep \- suspend execution for microsecond intervals .SH LIBRARY Standard C library .RI ( libc ", " \-lc ) .SH SYNOPSIS .nf .B "#include " .P .BI "int usleep(useconds_t " usec ); .fi .P .RS -4 Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .RE .P .BR usleep (): .nf 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 .\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED .fi .SH DESCRIPTION The .BR usleep () function suspends execution of the calling thread for (at least) \fIusec\fP microseconds. The sleep may be lengthened slightly by any system activity or by the time spent processing the call or by the granularity of system timers. .SH RETURN VALUE The .BR usleep () function returns 0 on success. On error, \-1 is returned, with .I errno set to indicate the error. .SH ERRORS .TP .B EINTR Interrupted by a signal; see .BR signal (7). .TP .B EINVAL \fIusec\fP is greater than or equal to 1000000. (On systems where that is considered an error.) .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 usleep () T} Thread safety MT-Safe .TE .SH STANDARDS None. .SH HISTORY 4.3BSD, POSIX.1-2001. POSIX.1-2001 declares it obsolete, suggesting .BR nanosleep (2) instead. Removed in POSIX.1-2008. .P On the original BSD implementation, and before glibc 2.2.2, the return type of this function is .IR void . The POSIX version returns .IR int , and this is also the prototype used since glibc 2.2.2. .P Only the .B EINVAL error return is documented by SUSv2 and POSIX.1-2001. .SH CAVEATS The interaction of this function with the .B SIGALRM signal, and with other timer functions such as .BR alarm (2), .BR sleep (3), .BR nanosleep (2), .BR setitimer (2), .BR timer_create (2), .BR timer_delete (2), .BR timer_getoverrun (2), .BR timer_gettime (2), .BR timer_settime (2), .BR ualarm (3) is unspecified. .SH SEE ALSO .BR alarm (2), .BR getitimer (2), .BR nanosleep (2), .BR select (2), .BR setitimer (2), .BR sleep (3), .BR ualarm (3), .BR useconds_t (3type), .BR time (7)