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       truncate, ftruncate - truncate a file to a specified length


       #include <unistd.h>
       #include <sys/types.h>

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

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       truncate(): _BSD_SOURCE || _XOPEN_SOURCE >= 500
       ftruncate(): _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
       _POSIX_C_SOURCE >= 200112L


       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 null bytes ('\0').

       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.


       On success, zero is returned.  On error, -1 is returned, and  errno  is
       set appropriately.


       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

       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

       EIO    An I/O error occurred updating the inode.

       EINTR  While blocked waiting to complete, the call was interrupted by a
              signal handler; see fcntl(2) and signal(7).

       EISDIR The named file is a directory.

       ELOOP  Too  many  symbolic  links  were  encountered in translating the

              A component of a pathname exceeded 255 characters, or an  entire
              pathname exceeded 1023 characters.

       ENOENT The named file does not exist.

              A component of the path prefix is not a directory.

       EPERM  The  underlying  file  system  does not support extending a file
              beyond its current size.

       EROFS  The named file resides on a read-only file system.

              The file is a pure procedure (shared text) file  that  is  being

       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 the  file
       descriptor, fd:

       EBADF  fd is not a valid descriptor.

       EBADF or EINVAL
              fd is not open for writing.

       EINVAL fd does not reference a regular file.


       4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).


       The  above  description  is  for  XSI-compliant  systems.  For non-XSI-
       compliant  systems,  the  POSIX  standard  allows  two  behaviors   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.  Like most Unix implementations, Linux
       follows the XSI requirement when  dealing  with  native  file  systems.
       However,  some  nonnative  file  systems  do  not permit truncate() and
       ftruncate() to be used to extend a file beyond its  current  length:  a
       notable example on Linux is VFAT.


       open(2), stat(2), path_resolution(7)


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