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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);

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 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(2).)

       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 4.2BSD).  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), path_resolution(2), stat(2)