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NAME

       write - write to a file descriptor

SYNOPSIS

       #include <unistd.h>

       ssize_t write(int fd, const void *buf, size_t count);

DESCRIPTION

       write()  writes  up  to  count bytes to the file referenced by the file
       descriptor fd from the buffer starting at buf.  POSIX requires  that  a
       read()  which  can  be  proved  to  occur  after a write() has returned
       returns the new data.   Note  that  not  all  file  systems  are  POSIX
       conforming.

RETURN VALUE

       On  success,  the  number of bytes written are returned (zero indicates
       nothing was written).  On error, -1  is  returned,  and  errno  is  set
       appropriately.   If  count  is zero and the file descriptor refers to a
       regular file, 0 will be returned without causing any other effect.  For
       a special file, the results are not portable.

ERRORS

       EAGAIN Non-blocking  I/O  has  been  selected  using O_NONBLOCK and the
              write would block.

       EBADF  fd is not a valid file descriptor or is not open for writing.

       EFAULT buf is outside your accessible address space.

       EFBIG  An  attempt  was  made  to  write  a  file  that   exceeds   the
              implementation-defined  maximum  file  size or the process’ file
              size limit, or to write at a  position  past  than  the  maximum
              allowed offset.

       EINTR  The  call  was  interrupted  by  a  signal  before  any data was
              written.

       EINVAL fd is attached to an object which is unsuitable for writing;  or
              the  file  was  opened  with  the  O_DIRECT flag, and either the
              address specified in buf, the value specified in count,  or  the
              current file offset is not suitably aligned.

       EIO    A low-level I/O error occurred while modifying the inode.

       ENOSPC The device containing the file referred to by fd has no room for
              the data.

       EPIPE  fd is connected to a pipe or socket whose reading end is closed.
              When  this  happens  the  writing  process  will  also receive a
              SIGPIPE signal.  (Thus, the write return value is seen  only  if
              the program catches, blocks or ignores this signal.)

       Other errors may occur, depending on the object connected to fd.

CONFORMING TO

       SVr4,  SVID,  POSIX,  X/OPEN,  4.3BSD.  SVr4 documents additional error
       conditions EDEADLK, ENOLCK, ENOLNK, ENOSR,  ENXIO,  or  ERANGE.   Under
       SVr4 a write may be interrupted and return EINTR at any point, not just
       before any data is written.

NOTES

       A successful return from write() does not make any guarantee that  data
       has been committed to disk.  In fact, on some buggy implementations, it
       does not even guarantee that space has successfully been  reserved  for
       the  data.   The  only way to be sure is to call fsync(2) after you are
       done writing all your data.

SEE ALSO

       close(2), fcntl(2), fsync(2),  ioctl(2),  lseek(2),  open(2),  read(2),
       select(2), fwrite(3), writev(3)