truncate(3C)                                                   truncate(3C)

NAME
     truncate, ftruncate, truncate64, ftruncate64 - set a file to a speci-
     fied length

SYNOPSIS
     #include <unistd.h>

     int truncate(const char *path, offt length);

     int ftruncate(int fildes, offt length);

     int truncate64(const char *path, off64t length);

     int ftruncate64(int fildes, off64t 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
     stctime and stmtime fields of the file, and if the file is a regular
     file, the SISUID and SISGID bits of the file mode may be cleared.

     These functions are used only on pre-existing files and so do not have
     the potential programming hazard as does creat().

     When ftruncate() is used to increase the size of a file, the semantics
     are similar to a write() of zeroes to the file. For consistency with
     write(), the ftruncate() function will fail when the request is beyond
     the offset maximum (even if the effect of the request would be to
     shorten the file).

     There is no functional difference between truncate()/ftruncate() and
     truncate64()/ftruncate64(), except for the interpretation of off64t
     [see lfs(5)].




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truncate(3C)                                                   truncate(3C)

ERRORS
     The following error code descriptions are function-specific. You will
     find a general description in introprm2(2) or in errno(5).

     ftruncate() and truncate() fail if one or more of the following are
     true:

     EINTR         A signal was caught during the execution of truncate().

     EINVAL        The length argument was less than 0.

     EIO           An I/O error occurred while reading from or writing to
                   the file system.

     EFBIG or EINVAL
                   The length argument was greater than the maximum file
                   size.

     truncate() fails if one or more of the following are true:

     EACCES        Search permission is denied on a component of the path
                   prefix.

     EACCES        Write permission is denied for the file referred to by
                   path.

     EFAULT        path points outside the process' allocated address
                   space.

     EISDIR        The file referred to by path is a directory.

     ELOOP         Too many symbolic links were encountered in translating
                   path.

     EMFILE        The maximum number of file descriptors available to the
                   process has been reached.

     EMULTIHOP     Components of path require hopping to multiple remote
                   machines and file system type does not allow it.

     ENAMETOOLONG  The length of a path component exceeds NAMEMAX charac-
                   ters, or the length of path exceeds PATHMAX characters.

     ENFILE        Could not allocate any more space for the system file
                   table.

     ENOENT        Either a component of the path prefix or the file
                   referred to by path does not exist.

     ENOLINK       path points to a remote machine and the link to that
                   machine is no longer active.



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truncate(3C)                                                   truncate(3C)

     ENOTDIR       A component of the path prefix of path is not a direc-
                   tory.

     EROFS         The file referred to by path resides on a read-only file
                   system.

     ETXTBSY       The file referred to by path is a pure procedure (shared
                   text) file that is being executed.

     ftruncate() fails if one or more of the following are true:

     EAGAIN        The file exists, mandatory file/record locking is set,
                   and there are outstanding record locks on the file [see
                   chmod(2)].

     EBADF or EINVAL
                   fildes is not a file descriptor open for writing.

     EFBIG         The file is a regular file and length is greater than
                   the offset maximum established in the open file descrip-
                   tion associated with fildes.

     ENOLINK       fildes points to a remote machine and the link to that
                   machine is no longer active.

     EINVAL        The fildes argument references a file that was opened
                   without write permission.

     The truncate() function may fail if:

     ENAMETOOLONG  Pathname resolution of a symbolic link produced an
                   intermediate result whose length exceeds PATHMAX.

RESULT
     Upon successful completion, a value of 0 is returned. Otherwise, a
     value of -1 is returned and errno is set to indicate the error.

SEE ALSO
     fcntl(2), open(2), unistd(4), lfs(5).















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