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



NAME
       fallocate - manipulate file space

SYNOPSIS
       #define _GNU_SOURCE
       #include <fcntl.h>

       int fallocate(int fd, int mode, off_t offset, off_t len);

DESCRIPTION
       This  is  a  non-portable,  Linux-specific system call.  For the portable, POSIX.1-specified method of ensuring
       that space is allocated for a file, see posix_fallocate().

       fallocate() allows the caller to directly manipulate the allocated disk space for the file referred  to  by  fd
       for the byte range starting at offset and continuing for len bytes.

       The mode argument determines the operation to be performed on the given range.  Currently only one flag is sup-
       ported for mode:

       FALLOC_FL_KEEP_SIZE
              This flag allocates and initializes to zero the disk space within the range specified by offset and len.
              After a successful call, subsequent writes into this range are guaranteed not to fail because of lack of
              disk space.  Preallocating zeroed blocks beyond the end of the file  is  useful  for  optimizing  append
              workloads.   Preallocating  blocks  does not change the file size (as reported by stat(2)) even if it is
              less than offset+len.

       If FALLOC_FL_KEEP_SIZE flag is not specified in mode, the default behavior is almost same as when this flag  is
       specified.   The  only  difference is that on success, the file size will be changed if offset + len is greater
       than the file size.  This default behavior closely resembles the behavior  of  the  posix_fallocate(3)  library
       function, and is intended as a method of optimally implementing that function.

       Because  allocation  is  done in block size chunks, fallocate() may allocate a larger range than that which was
       specified.

RETURN VALUE
       fallocate() returns zero on success, and -1 on failure.

ERRORS
       EBADF  fd is not a valid file descriptor, or is not opened for writing.

       EFBIG  offset+len exceeds the maximum file size.

       EINTR  A signal was caught during execution.

       EINVAL offset was less than 0, or len was less than or equal to 0.

       EIO    An I/O error occurred while reading from or writing to a file system.

       ENODEV fd does not refer to a regular file or a directory.  (If fd  is  a  pipe  or  FIFO,  a  different  error
              results.)

       ENOSPC There is not enough space left on the device containing the file referred to by fd.

       ENOSYS The file system containing the file referred to by fd does not support this operation.

       EOPNOTSUPP
              The mode is not supported by the file system containing the file referred to by fd.

VERSIONS
       fallocate() is available on Linux since kernel 2.6.23.  Support is provided by glibc since version 2.10.

CONFORMING TO
       fallocate() is Linux-specific.

SEE ALSO
       ftruncate(2), posix_fadvise(3), posix_fallocate(3)

COLOPHON
       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 http://www.kernel.org/doc/man-pages/.



Linux                             2009-03-13                      FALLOCATE(2)