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truncate(2)							   truncate(2)

       truncate, ftruncate - Change file length

       #include <unistd.h>

       int truncate(
	       const char *path,
	       off_t length ); int ftruncate(
	       int filedes,
	       off_t length );

       Interfaces  documented on this reference page conform to industry stan‐
       dards as follows:

       ftruncate(), truncate(): XSH4.2, XSH5.0

       Refer to the standards(5) reference page	 for  more  information	 about
       industry standards and associated tags.

       Specifies  the  name  of	 a  file  that	is opened, truncated, and then
       closed.	The path parameter must point to a pathname which names a reg‐
       ular  file  for	which the calling process has write permission. If the
       path parameter refers to a  symbolic  link,  the	 length	 of  the  file
       pointed to by the symbolic link is truncated.  Specifies the descriptor
       of a file that must be open for writing.	 Specifies the new  length  of
       the file in bytes.

       The truncate() and ftruncate() functions change the length of a file to
       the size in bytes specified by the length parameter.  If the new length
       is  less than the previous length, the truncate() and ftruncate() func‐
       tions remove all data beyond length bytes from the specified file.  All
       file  data  between the new end-of-file and the previous end-of-file is
       discarded. If the new length is greater than the previous  length,  one
       byte  of	 zero  (0x00) is written at the offset of the new length.  The
       space in between the previous end-of-file and the  new  end-of-file  is
       left  as	 a  hole;  that	 is,  no  blocks are allocated to the space in
       between the previous last block and the new last block.

       Full blocks are returned to the file system so that they	 can  be  used
       again,  and the file size is changed to the value of the length parame‐

       The truncate() and ftruncate() functions have no effect on FIFO special
       files or directories. These functions do not modify the seek pointer of
       the file.

       Upon successful completion, the truncate()  and	ftruncate()  functions
       mark  the  st_ctime  and st_mtime fields of the file for update. If the
       file is a regular file, the ftruncate() and truncate() functions	 clear
       the S_ISUID and S_ISGID attributes of the file.

       [Tru64  UNIX]  If  the file has enforced file locking enabled and there
       are file locks on the file,  the	 truncate()  or	 ftruncate()  function

       Upon  successful	 completion,  a	 value of 0 (zero) is returned. If the
       truncate() or ftruncate() function fails, it returns a value of -1, and
       errno is set to indicate the error.

       The  ftruncate()	 and  truncate()  functions set errno to the specified
       values for the following conditions: [Tru64 UNIX]  The write  operation
       failed due to an enforced write lock on the file.

	      [Tru64  UNIX]  The  file	has enforced mode file locking enabled
	      and there are file locks on the file.  The length parameter  was
	      greater  than the maximum file size.  A signal was caught during
	      execution.  The length parameter was less than 0 (zero).

	      [Tru64 UNIX]  The file is not a  regular	file.	An  I/O	 error
	      occurred while reading from or writing to a file system.	[Tru64
	      UNIX]  The process' root or current directory is	located	 in  a
	      virtual file system that has been unmounted.

       In  addition, the ftruncate() function sets errno to the specified val‐
       ues for the following conditions: [Tru64 UNIX]  Write access permission
       to  the	file  was  denied.   The filedes parameter is not a valid file
       descriptor open for writing.  The fildes parameter  references  a  file
       that  was  opened  without  write  permission.	[Tru64 UNIX]  The file
       resides on a read-only file system.

       In addition, the truncate() function fails if errors occur  that	 apply
       to  any service requiring pathname resolution, or if one of the follow‐
       ing are true: A component of the path prefix denies search  permission,
       or  write permission is denied on the file.  The named file is a direc‐
       tory.  Too many symbolic links were encountered in resolving path.  The
       size of the pathname exceeds PATH_MAX or a pathname component is longer
       than NAME_MAX.

	      Pathname resolution of a symbolic link produced an  intermediate
	      result whose length exceeds PATH_MAX.  A component of the speci‐
	      fied pathname does not exist, or the path parameter points to an
	      empty  string.   A  component of the path prefix is not a direc‐
	      tory.  The file resides on a read-only file system.

       Functions: chmod(2), fcntl(2), open(2)

       Standards: standards(5)


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