truncate, ftruncate - Changes file length
const char *path,
Interfaces documented on this reference page conform to industry standards
ftruncate(), truncate(): XSH4.2
Refer to the standards(5) reference page for more information about indus-
try standards and associated tags.
path Specifies the name of a file that is opened, truncated, and then
closed. The path parameter must point to a pathname which names
a regular file for which the calling process has write permis-
sion. If the path parameter refers to a symbolic link, the
length of the file pointed to by the symbolic link is truncated.
filedes Specifies the descriptor of a file that must be open for writing.
length Specifies the new length of the file in bytes.
The truncate() and ftruncate() functions change the length of a file to the
size in bytes specified by the length parameter. If the new length is less
than the previous length, the truncate() and ftruncate() functions remove
all data beyond length bytes from the specified file. All file data
between the new end-of-file and the previous end-of-file is discarded. If
the new length is greater than the previous length, one byte of zero (0x00)
is written at the offset of the new length. The space in between the pre-
vious end-of-file and the new end-of-file is left as a hole; that is, no
blocks are allocated to the space in between the previous last block and
the new last block.
Full blocks are returned to the file system so that they can be used again,
and the file size is changed to the value of the length parameter.
The truncate() and ftruncate() functions have no effect on FIFO special
files or directories. These functions do not modify the seek pointer of
Upon successful completion, the truncate() and ftruncate() functions mark
the st_ctime and st_mtime fields of the file for update. If the file is a
regular file, the ftruncate() and truncate() functions clear the S_ISUID
and S_ISGID attributes of the file.
If the file has enforced file locking enabled and there are file locks on
the file, the truncate() or ftruncate() function fails.
Upon successful completion, a value of 0 (zero) is returned. If the trun-
cate() or ftruncate() function fails, it returns a value of -1, and errno
is set to indicate the error.
The ftruncate() and truncate() functions set errno to the specified values
for the following conditions:
[EAGAIN] [Tru64 UNIX] The write operation failed due to an enforced write
lock on the file.
[Tru64 UNIX] The file has enforced mode file locking enabled and
there are file locks on the file.
[EFBIG] The length parameter was greater than the maximum file size.
[EINTR] A signal was caught during execution.
[EINVAL] The length parameter was less than 0 (zero).
[Tru64 UNIX] The file is not a regular file.
[EIO] An I/O error occurred while reading from or writing to a file
[ESTALE] [Tru64 UNIX] The process' root or current directory is located
in a virtual file system that has been unmounted.
In addition, the ftruncate() function sets errno to the specified values
for the following conditions:
[EACCES] [Tru64 UNIX] Write access permission to the file was denied.
[EBADF] The filedes parameter is not a valid file descriptor open for
[EINVAL] The fildes parameter references a file that was opened without
[EROFS] [Tru64 UNIX] The file resides on a read-only file system.
In addition, the truncate() function fails if errors occur that apply to
any service requiring pathname resolution, or if one of the following are
[EACCES] A component of the path prefix denies search permission, or write
permission is denied on the file.
[EISDIR] The named file is a directory.
[ELOOP] Too many symbolic links were encountered in resolving path.
The size of the pathname exceeds PATH_MAX or a pathname component
is longer than NAME_MAX.
[ENOENT] A component of the specified pathname does not exist, or the path
parameter points to an empty string.
[ENOTDIR] A component of the path prefix is not a directory.
[EROFS] The file resides on a read-only file system.
Functions: chmod(2), fcntl(2), open(2)