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


lseek - reposition read/write file offset


#include <sys/types.h> #include <unistd.h> off_t lseek(int fildes, off_t offset, int whence);


The lseek() function repositions the offset of the open file associated with the file descriptor fildes 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.


Upon successful completion, lseek() returns the resulting offset loca- tion 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.


EBADF fildes 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 fildes is associated with a pipe, socket, or FIFO.


SVr4, 4.3BSD, POSIX.1-2001.


Some devices are incapable of seeking and POSIX does not specify which devices must support lseek(). Linux specific restrictions: using lseek() on a tty device returns ESPIPE.


This document's use of whence is incorrect English, but maintained for historical reasons. When converting old code, substitute values for whence with the follow- ing 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 cur- rent file position pointer, so seeking on such files may be subject to race conditions.


dup(2), fork(2), open(2), fseek(3), lseek64(3), posix_fallocate(3) Linux 2001-09-24 LSEEK(2)

1994 Man-cgi 1.15, Panagiotis Christias <>