This document is a Mac OS X manual page. Manual pages are a command-line technology for providing documentation. You can view these manual pages locally using the man(1) command. These manual pages come from many different sources, and thus, have a variety of writing styles.

This manual page is associated with the Mac OS X developer tools. The software or headers described may not be present on your Mac OS X installation until you install the developer tools package. This package is available on your Mac OS X installation DVD, and the latest versions can be downloaded from developer.apple.com.

For more information about the manual page format, see the manual page for manpages(5).

TRUNCATE(2)                 BSD System Calls Manual                TRUNCATE(2)

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

SYNOPSIS
     #include <unistd.h>

     int
     ftruncate(int fildes, off_t length);

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

DESCRIPTION
     Truncate() causes the file named by path or referenced by fildes to be truncated or extended to length
     bytes in size.  If the file previously was larger than this size, the extra data is lost. If the file
     was smaller than this size, it will be extended as if by writing bytes with the value zero.  With
     ftruncate(), the file must be open for writing.

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
     The ftruncate() system call will fail if:

     [EBADF]            fildes is not a valid descriptor open for writing.

     [EFBIG]            The file is a regular file and length is greater than the offset maximum established
                        in the open file description associated with fildes.

     [EINVAL]           fildes references a socket, not a file.

     [EINVAL]           fildes is not open for writing.

     [EROFS]            The named file resides on a read-only file system.

     The truncate() system call will fail if:

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

     [EACCES]           The named file is not writable by the user.

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

     [EISDIR]           The named file is a directory.

     [ELOOP]            Too many symbolic links are encountered in translating the pathname.  This is taken
                        to be indicative of a looping symbolic link.

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

     [ENOENT]           The named file does not exist.

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

     The ftruncate() and truncate() system calls will fail if:

     [EFBIG]            The length argument was greater than the maximum file size.

     [EINTR]            A signal is caught during execution.

     [EINVAL]           The length argument is less than 0.

     [EIO]              An I/O error occurred while reading from or writing to a file system.

SEE ALSO
     open(2)

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

     Use of truncate() to extend a file is not portable.

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

4.2 Berkeley Distribution        June 4, 1993        4.2 Berkeley Distribution