TRUNCATE(2)

NAME
truncate, ftruncate - truncate a file to a specified length

SYNOPSIS
#include <unistd.h>

int truncate(const char *path, off_t length);
int ftruncate(int fd, off_t length);

DESCRIPTION
Truncate causes the file named by path or 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, 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
For truncate:

ENOTDIR
    A component of the path prefix is not a directory.

ENAMETOOLONG
    A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.

ENOENT
    The named file does not exist.

EACCES
    Search permission is denied for a component of the path prefix.

EACCES
    The named file is not writable by the user.

ELOOP
    Too many symbolic links were encountered in translating the pathname.

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.

For ftruncate:

EBADF
    The fd is not a valid descriptor.

EINVAL
    The fd references a socket, not a file.

EINVAL
    The fd is not open for writing.

CONFORMING TO
4.4BSD, SVr4 (these function calls first appeared in BSD 4.2). SVr4 documents additional truncate error conditions EINTR, EMFILE, EMULTIHP, ENAMETOOLONG, ENFILE, ENOLINK, ENOTDIR. SVr4 documents for ftruncate additional EAGAIN and EINTR error conditions. POSIX has ftruncate but not truncate.

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)