TRUNCATE(2)

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

LIBRARY
libc

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 have a size of length bytes. If the file previously was larger than this size, the extra data is discarded. If it was previously shorter than length, its size is increased to the specified value and the extended area appears as if it were zero-filled.

With ftruncate(), the file must be open for writing; for truncate(), the process must have write permissions for the file.

RETURN VALUES
A value of 0 is returned if the call succeeds. If the call fails a -1 is returned, and the global variable errno specifies the error.

ERRORS
Error return codes common to truncate() and ftruncate() are:

[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.

[ENOSPC]
    There was no space in the filesystem to complete the operation.

Error codes specific to truncate() are:

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

[ENAMETOOLONG]
    A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} characters.

[ENOENT]
    The named file does not exist.

[EACCES]
    Search permission is denied for a component of the path prefix, or the named file is not writable by the user.

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

[EFAULT]
    path points outside the process's allocated address space.

Error codes specific to ftruncate() are:

[EBADF]
    The fd is not a valid descriptor.

[EINVAL]
    The fd references a socket, not a file, or the fd is not open for writing.

SEE ALSO
open(2)

STANDARDS
Use of truncate() to extend a file is an p1003.1-2004 extension, and is thus not portable. Files can be extended in a portable way seeking (using lseek(2)) to the required size and writing a single character with write(2).

HISTORY
The truncate() and ftruncate() function calls appeared in 4.2BSD.

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