TRUNCATE(2)                                         Linux Programmer's Manual                                        TRUNCATE(2)



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);

   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

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 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.

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(7).)

       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.

       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 pathname.

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

       ENOENT The named file does not exist.

       ENOTDIR
              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.

       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 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.

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

NOTES
       The above description is for XSI-compliant systems.  For non-XSI-compliant systems, the POSIX standard allows two  behav-
       iors  for  ftruncate() when length exceeds the file length (note that truncate() is not specified at all in such an envi-
       ronment): 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.

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

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2009-02-28                                                TRUNCATE(2)