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 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
           || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

       ftruncate():
           _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
           || /* Since glibc 2.3.5: */ _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  While blocked waiting to complete, the call was interrupted by a signal handler; see fcntl(2)  and
              signal(7).

       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 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 filesystem does not support extending a file beyond its current size.

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

       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 details in DESCRIPTION are 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 filesystems.
       However, some nonnative filesystems do not permit truncate() and ftruncate() to be used to extend a  file
       beyond its current length: a notable example on Linux is VFAT.

       The  original  Linux  truncate()  and  ftruncate()  system  calls  were not designed to handle large file
       offsets.  Consequently, Linux 2.4 added truncate64() and ftruncate64() system  calls  that  handle  large
       files.   However,  these  details  can  be  ignored  by applications using glibc, whose wrapper functions
       transparently employ the more recent system calls where they are available.

       On some 32-bit architectures, the calling signature for  these  system  calls  differ,  for  the  reasons
       described in syscall(2).

BUGS

       A  header  file  bug in glibc 2.12 meant that the minimum value of _POSIX_C_SOURCE required to expose the
       declaration of ftruncate() was 200809L instead of 200112L.  This has been fixed in later glibc versions.

SEE ALSO

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

COLOPHON

       This page is part of release 3.54 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/.