NAME
ftruncate, truncate — truncate a file to a specified length
SYNOPSIS
#include <unistd.h>
int ftruncate(int fildes, off_t length);
int truncate(const char *path, off_t length);
DESCRIPTION
The
ftruncate()
function causes the regular file referenced by
fildes
to have a size of
length
bytes.
The
truncate()
function causes the regular file named by
path
to have a size of
length
bytes.
The effect of
ftruncate()
and
truncate()
on other types of files is unspecified. If the file
previously was larger than
length,
the extra data is lost. If it was previously shorter than
length,
bytes between the old and new lengths are read as zeroes. With
ftruncate(),
the file must be open for writing; for
truncate(),
the process must have write permission for the file.
If the request would cause the file size to exceed
the soft file size limit for the process, the
request will fail and the implementation will
generate the
SIGXFSZ
signal for the process.
These functions do not modify the file offset for
any open file descriptions associated with the file.
On successful completion, if the file size is
changed, these functions will mark for update the
st_ctime
and
st_mtime
fields of the file, and if the file is a regular file, the
S_ISUID
and
S_ISGID
bits of the file mode may be cleared.
RETURN VALUE
Upon successful completion,
ftruncate()and
truncate()
returns 0. Otherwise a -1 is returned, and
errno
is set to indicate the error.
ERRORS
If
ftruncate()
or
truncate()
fails,
errno
is set to one of the following values:
- EINTR
A signal was caught during execution.
- EINVAL
The
length
argument was less than 0.
- [EFBIG] or [EINVAL]
The
length
argument was greater than the maximum file size.
- EIO
An I/O error occurred while reading from or writing to a file system.
- EAGAIN
Enforcement mode file/record locking is set (see
chmod(2)),
and there are outstanding record locks on the file with the
lockf(),
flock(),
or
fcntl()
system calls.
If
ftruncate()
fails,
errno
is set to one of the following values:
- [EBADF] or [EINVAL]
The
fildes
argument is not a file descriptor open for writing.
- EDQUOT
The user's disk quota block limit has been reached for this file system.
- EINVAL
The
fildes
argument references a file that was opened without write permission.
If
truncate()
fails,
errno
is set to one of the following values:
- EACCES
A component of the
path
prefix denies search permission, or write permission is denied
on the file.
- EDQUOT
The user's disk quota block limit has been reached for this file system.
- EFAULT
path
points outside the process's allocated address space. The
reliable detection of this error is implementation dependent.
- EISDIR
The named file is a directory.
- ELOOP
Too many symbolic links were encountered in resolving
path.
- ENAMETOOLONG
Pathname resolution produced an intermediate result
whose length exceeds
PATH_MAX
bytes, or the length of a component of the pathname exceeds
NAME_MAX
bytes.
- ENOENT
A component of
path
does not name an existing file or path is an empty string.
- ENOTDIR
A component of the
path
prefix of path 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.
AUTHOR
truncate()
was developed by the University of California, Berkeley.
CHANGE HISTORY
First released in Issue 4, Version 2.
STANDARDS CONFORMANCE
truncate(): AES
ftruncate(): AES, SVID3
Printable version
