NAME

truncate, ftruncate - truncate a file to a specified length

SYNOPSIS

#include <unistd> int ftruncate(int fd, off_t length);

DESCRIPTION

ftruncate(2) causes the file referenced by fd to be truncated to at most length bytes in size. If the file previously was larger than this size, the extra data is lost. If the file previously was shorter, it is unspecified whether the file is left unchanged or is extended. In the latter case the extended part reads as zero bytes. With ftruncate(2), the file must be open for writing.

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

EBADF

The fd is not a valid descriptor.

EINVAL

The fd references a socket, not a file. (what happens if you call it on a pipe?)

EINVAL

The fd is not open for writing.

EACCES

The named file is not writable by the user.

EISDIR

The named file is a directory.

EROFS

The named file resides on a read-only file system.

ETXTBSY

The file is a pure procedure (shared text) file that is being executed.

EIO

An I/O error occurred updating the inode.

EFAULT

Path points outside the process's allocated address space.

CONFORMING TO

4.4BSD, SVr4 (these function calls first appeared in BSD 4.2). SVr4 documents for ftruncate(2) additional EAGAIN and EINTR error conditions. POSIX has ftruncate(2) but not truncate(2).

The POSIX standard does not define what happens if the file has fewer bytes than length.

BUGS

These calls should be generalized to allow ranges of bytes in a file to be discarded.

SEE ALSO

open(2), truncate(2)