Section: Linux Programmer's Manual (2)
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truncate, ftruncate - truncate a file to a specified length
int truncate(const char *path, off_t length);
int ftruncate(int fd, off_t length);
functions cause the regular file named by
or referenced by
to be truncated to a size of precisely
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 ('\0').
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
for the file are updated,
and the set-user-ID and set-group-ID permission bits may be cleared.
the file must be open for writing; with
the file must be writable.
On success, zero is returned. On error, -1 is returned, and
is set appropriately.
Search permission is denied for a component of the path prefix,
or the named file is not writable by the user.
points outside the process's allocated address space.
is larger than the maximum file size. (XSI)
A signal was caught during execution.
is negative or larger than the maximum file size.
An I/O error occurred updating the inode.
The named file is a directory.
Too many symbolic links were encountered in translating the pathname.
A component of a pathname exceeded 255 characters,
or an entire pathname exceeded 1023 characters.
The named file does not exist.
A component of the path prefix is not a directory.
The underlying file system does not support extending
a file beyond its current size.
The named file resides on a read-only file system.
The file is a pure procedure (shared text) file that is being executed.
the same errors apply, but instead of things that can be wrong with
we now have things that can be wrong with
is not a valid descriptor.
- EBADF or EINVAL
is not open for writing.
does not reference a regular file.
4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).
The above description is for XSI-compliant systems.
For non-XSI-compliant systems, the POSIX standard allows
two behaviours for
exceeds the file length
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
to be used to extend a file beyond its current length:
a notable example on Linux is VFAT.
- RETURN VALUE
- CONFORMING TO
- SEE ALSO
linux.jgfs.net manual pages