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TRUNCATE(2)                   System Calls Manual                  TRUNCATE(2)

     truncate, ftruncate - truncate a file to a specified length

     Standard C Library (libc, -lc)

     #include <unistd.h>

     truncate(const char *path, off_t length);

     ftruncate(int fd, off_t length);

     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.

     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.

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

     [EINVAL]           The length argument was less than 0.

     [EIO]              An I/O error occurred updating the inode.

     [EISDIR]           The named file is a directory.

     [ENOSPC]           There was no space in the file system to complete the

     [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.

     Error codes specific to truncate() are:

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

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

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

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

     [ENOENT]           The named file does not exist.

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

     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.

     fdiscard(2), open(2)

     Use of truncate() to extend a file is an IEEE Std 1003.1-2004 ("POSIX.1")
     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).

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

NetBSD 10.99                     July 23, 2014                    NetBSD 10.99