truncate(2) -- Linux man page
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);
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 zero bytes.
The file pointer is not changed.
If the size changed, then the ctime and mtime fields for the file
are updated, and suid and sgid mode 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.
- 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.
- 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 path name exceeded 1023 characters.
- ENOENT
-
The named file does not exist.
- ENOTDIR
-
A component of the path prefix is not a directory.
- 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
fd:
- EBADF
-
The
fd
is not a valid descriptor.
- EBADF or EINVAL
-
The
fd
is not open for writing.
- EINVAL
-
The
fd
does not reference a regular file.
CONFORMING TO
4.4BSD, SVr4 (these function calls first appeared in BSD 4.2).
POSIX 1003.1-1996 has
ftruncate.
POSIX 1003.1-2001 also has
truncate,
as an XSI extension.
SVr4 documents additional
truncate
error conditions EMFILE, EMULTIHP, ENFILE, ENOLINK. SVr4 documents for
ftruncate
an additional EAGAIN error condition.
NOTES
The above description is for XSI-compliant systems.
For non-XSI-compliant systems, the POSIX standard allows
two behaviours 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.
(Most Unices follow the XSI requirement.)
SEE ALSO
open(2)
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