The
truncate()
and
ftruncate()
functions cause the regular file named by
path
or referenced by
fd
to be truncated to a size of precisely
length
bytes.
If the file previously was larger than this size, the extra data is lost.
If the file previously was shorter, it is extended, and
the extended part reads as null bytes (aq\0aq).
The file offset is not changed.
If the size changed, then the st_ctime and st_mtime fields
(respectively, time of last status change and
time of last modification; see
stat(2))
for the file are updated,
and the set-user-ID and set-group-ID permission bits may be cleared.
With
ftruncate(),
the file must be open for writing; with
truncate(),
the file must be writable.
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
For
truncate():
EACCES
Search permission is denied for a component of the path prefix,
or the named file is not writable by the user.
(See also
path_resolution(7).)
EFAULT
Path
points outside the process's allocated address space.
EFBIG
The argument
length
is larger than the maximum file size. (XSI)
EINTR
A signal was caught during execution.
EINVAL
The argument
length
is negative or larger than the maximum file size.
EIO
An I/O error occurred updating the inode.
EINTR
While blocked waiting to complete,
the call was interrupted by a signal handler; see
fcntl(2)
and
signal(7).
EISDIR
The named file is a directory.
ELOOP
Too many symbolic links were encountered in translating the pathname.
ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire pathname exceeded 1023 characters.
ENOENT
The named file does not exist.
ENOTDIR
A component of the path prefix is not a directory.
EPERM
The underlying file system does not support extending
a file beyond its current size.
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.
For
ftruncate()
the same errors apply, but instead of things that can be wrong with
path,
we now have things that can be wrong with the file descriptor,
fd:
EBADF
fd
is not a valid descriptor.
EBADF or EINVAL
fd
is not open for writing.
EINVAL
fd
does not reference a regular file.
CONFORMING TO
4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).
NOTES
The above description is for XSI-compliant systems.
For non-XSI-compliant systems, the POSIX standard allows
two behaviors for
ftruncate()
when
length
exceeds the file length
(note that
truncate()
is not specified at all in such an environment):
either returning an error, or extending the file.
Like most Unix implementations, Linux follows the XSI requirement
when dealing with native file systems.
However, some non-native file systems do not permit
truncate()
and
ftruncate()
to be used to extend a file beyond its current length:
a notable example on Linux is VFAT.
This page is part of release 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
