TRUNCATE
Section: Linux Programmer's Manual (2)
Updated: 2013-04-01
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NAME
truncate, ftruncate - truncate a file to a specified length
SYNOPSIS
#include <unistd.h>
#include <sys/types.h>
int truncate(const char *path, off_t length);
int ftruncate(int fd, off_t length);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
truncate():
-
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
ftruncate():
-
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.3.5: */ _POSIX_C_SOURCE >= 200112L
DESCRIPTION
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 ('\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
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
-
While blocked waiting to complete,
the call was interrupted by a signal handler; see
fcntl(2)
and
signal(7).
- EINVAL
-
The argument
length
is negative or larger than the maximum file size.
- EIO
-
An I/O error occurred updating the inode.
- 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 filesystem does not support extending
a file beyond its current size.
- EROFS
-
The named file resides on a read-only filesystem.
- 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 details in DESCRIPTION are 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 filesystems.
However, some nonnative filesystems do not permit
truncate()
and
ftruncate()
to be used to extend a file beyond its current length:
a notable example on Linux is VFAT.
The original Linux
truncate()
and
ftruncate()
system calls were not designed to handle large file offsets.
Consequently, Linux 2.4 added
truncate64()
and
ftruncate64()
system calls that handle large files.
However, these details can be ignored by applications using glibc, whose
wrapper functions transparently employ the more recent system calls
where they are available.
On some 32-bit architectures,
the calling signature for these system calls differ,
for the reasons described in
syscall(2).
BUGS
A header file bug in glibc 2.12 meant that the minimum value of
_POSIX_C_SOURCE
required to expose the declaration of
ftruncate()
was 200809L instead of 200112L.
This has been fixed in later glibc versions.
SEE ALSO
open(2),
stat(2),
path_resolution(7)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- BUGS
-
- SEE ALSO
-
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Time: 02:54:45 GMT, September 18, 2014