WRITE(2)                   Linux Programmer's Manual                  WRITE(2)
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  con-
       forming.

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 may be returned, or an error could be detected.  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 implementa-
              tion-defined  maximum file size or the process' file size limit,
              or to write at a position past the maximum allowed offset.

       EINTR  The call was interrupted by a signal before any data  was  writ-
              ten.

       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  SIG-
              PIPE  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, 4.3BSD, POSIX.1-2001.

       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), pwrite(2),
       read(2), select(2), writev(3), fwrite(3)

Linux 2.0.32                      2001-12-13                          WRITE(2)