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NAME

       fallocate - manipulate file space

SYNOPSIS

       #define _GNU_SOURCE             /* See feature_test_macros(7) */
       #include <fcntl.h>

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

DESCRIPTION

       This  is  a nonportable, Linux-specific system call.  For the portable,
       POSIX.1-specified method of ensuring that  space  is  allocated  for  a
       file, see posix_fallocate(3).

       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.   Details  of  the  supported  operations  are  given   in   the
       subsections below.

   Allocating disk space
       The default operation (i.e., mode is zero) of fallocate() allocates and
       initializes to zero the disk space within the range specified by offset
       and  len.   The  file  size (as reported by stat(2)) 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.

       After  a successful call, subsequent writes into the range specified by
       offset and len are guaranteed not to  fail  because  of  lack  of  disk
       space.

       If  the  FALLOC_FL_KEEP_SIZE flag is specified in mode, the behavior of
       the call is similar, but the file size will  not  be  changed  even  if
       offset+len  is greater than the file size.  Preallocating zeroed blocks
       beyond the end of the file in this  manner  is  useful  for  optimizing
       append workloads.

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

   Deallocating file space
       Specifying the FALLOC_FL_PUNCH_HOLE flag (available since Linux 2.6.38)
       in  mode  deallocates  space  (i.e.,  creates a hole) in the byte range
       starting at offset and continuing for len bytes.  Within the  specified
       range,  partial  file  system  blocks are zeroed, and whole file system
       blocks are removed from the file.  After a successful call,  subsequent
       reads from this range will return zeroes.

       The  FALLOC_FL_PUNCH_HOLE flag must be ORed with FALLOC_FL_KEEP_SIZE in
       mode; in other words, even when punching off the end of the  file,  the
       file size (as reported by stat(2)) does not change.

       Not  all  file  systems  support FALLOC_FL_PUNCH_HOLE; if a file system
       doesn't support the operation, an error is returned.

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 This kernel does not implement fallocate().

       EOPNOTSUPP
              The  file  system containing the file referred to by fd does not
              support this operation; or the mode is not supported by the file
              system containing the file referred to by fd.

       EPERM  The  file referred to by fd is marked immutable (see chattr(1)).
              Or: mode specifies FALLOC_FL_PUNCH_HOLE and the file referred to
              by fd is marked append-only (see chattr(1)).

       ESPIPE fd refers to a pipe or FIFO.

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 3.44 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/.