LSEEK(2) Linux Programmer's Manual LSEEK(2)
lseek - reposition read/write file offset
off_t lseek(int fd, off_t offset, int whence);
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:
The offset is set to offset bytes.
The offset is set to its current location plus offset bytes.
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 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.
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.
The resulting file offset cannot be represented in an off_t.
ESPIPE fd is associated with a pipe, socket, or FIFO.
SVr4, 4.3BSD, POSIX.1-2001.
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-
On Linux, using lseek() on a tty device returns ESPIPE.
When converting old code, substitute values for whence with the following macros:
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.
dup(2), fork(2), open(2), fseek(3), lseek64(3), posix_fallocate(3)
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-
Linux 2001-09-24 LSEEK(2)