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LSEEK(2)			    Linux Programmer's Manual				 LSEEK(2)

NAME
       lseek - reposition read/write file offset

SYNOPSIS
       #include <sys/types.h>
       #include <unistd.h>

       off_t lseek(int fd, off_t offset, int whence);

DESCRIPTION
       The  lseek()  function  repositions  the  offset of the open file associated with the file
       descriptor fd to the argument offset according to the directive whence as follows:

       SEEK_SET
	      The offset is set to offset bytes.

       SEEK_CUR
	      The offset is set to its current location plus offset bytes.

       SEEK_END
	      The offset is set to the size of the file plus offset bytes.

       The lseek() function allows the file offset to be set beyond the end of the file (but this
       does not change the size of the file).  If data is later written at this point, subsequent
       reads of the data in the gap (a "hole") return null bytes ('\0') until  data  is  actually
       written into the gap.

RETURN VALUE
       Upon  successful  completion, lseek() returns the resulting offset location as measured in
       bytes from the beginning of the file.  Otherwise, a value of (off_t) -1	is  returned  and
       errno is set to indicate the error.

ERRORS
       EBADF  fd is not an open file descriptor.

       EINVAL whence  is  not  one  of SEEK_SET, SEEK_CUR, SEEK_END; or the resulting file offset
	      would be negative, or beyond the end of a seekable device.

       EOVERFLOW
	      The resulting file offset cannot be represented in an off_t.

       ESPIPE fd is associated with a pipe, socket, or FIFO.

CONFORMING TO
       SVr4, 4.3BSD, POSIX.1-2001.

NOTES
       This document's use of whence is incorrect English, but maintained for historical reasons.

       Some devices are incapable of seeking and POSIX does not specify which devices  must  sup-
       port lseek().

       On Linux, using lseek() on a tty device returns ESPIPE.

       When converting old code, substitute values for whence with the following macros:

	old	  new
       0	SEEK_SET
       1	SEEK_CUR
       2	SEEK_END
       L_SET	SEEK_SET

       L_INCR	SEEK_CUR
       L_XTND	SEEK_END

       SVr1-3 returns long instead of off_t, BSD returns int.

       Note  that  file  descriptors created by dup(2) or fork(2) share the current file position
       pointer, so seeking on such files may be subject to race conditions.

SEE ALSO
       dup(2), fork(2), open(2), fseek(3), lseek64(3), posix_fallocate(3)

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A  description  of  the
       project,   and	information  about  reporting  bugs,  can  be  found  at  http://www.ker-
       nel.org/doc/man-pages/.

Linux					    2001-09-24					 LSEEK(2)
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