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

       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 trun-
       cated 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 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  sig-

       EISDIR The named file is a directory.

       ELOOP  Too many symbolic links were encountered in translating the pathname.

              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 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.

       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 non-native file systems
       do not permit truncate() and ftruncate() to be used to extend a file beyond its current length: a notable exam-
       ple on Linux is VFAT.

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

       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at

Linux                             2009-02-28                       TRUNCATE(2)