prealloc(2)prealloc(2)NAMEprealloc - preallocate fast disk storage
SYNOPSISDESCRIPTION
is used to preallocate space on a disk for faster storage operations.
fildes is a file descriptor obtained from a or system call for an ordi‐
nary file of zero length. It must be opened writable, because it will
be written to by size is the size in bytes to be preallocated for the
file specified by fildes. At least size bytes will be allocated.
Space is allocated in an implementation-dependent fashion for fast
sequential reads and writes. The EOF in an extended file is left at
the end of the preallocated area. The current file pointer is left at
zero. The file is zero-filled.
Using on a file does not give the file an attribute that is inherited
when copying or restoring the file using a program such as or (see
cp(1) and tar(1)). It simply ensures that disk space has been preallo‐
cated for size bytes in a manner suited for sequential access. The
file can be extended beyond these limits by operations past the origi‐
nal end of file. However, this space will not necessarily be allocated
using any special strategy.
RETURN VALUE
Upon successful completion, returns 0; otherwise, it returns −1 and
sets to indicate the error.
ERRORS
fails and no disk space is allocated if any of the following conditions
are encountered:
[EBADF] fildes is not a valid open file descriptor opened
for writing.
[EDQUOT] User's disk quota block limit has been reached
for this file system.
[EFBIG] size exceeds the maximum file size or the
process's file size limit. See ulimit(2).
[ENOSPC] Not enough space is left on the device to allo‐
cate the requested amount; no space was allo‐
cated.
[ENOTEMPTY] fildes not associated with an ordinary file of
zero length.
EXAMPLES
Assuming a process has opened a file for writing, the following call to
preallocates at least 50000 bytes on disk for the file represented by
file descriptor outfd:
WARNINGS
Allocation of the file space is highly dependent on current disk usage.
A successful return does not tell you how fragmented the file actually
might be if the disk is nearing its capacity.
AUTHOR
was developed by HP.
SEE ALSOprealloc(1), creat(2), dup(2), fcntl(2), open(2), prealloc64(2),
read(2), ulimit(2), write(2).
prealloc(2)
