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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 from the buffer pointed buf	to the
       file referred to	by the file descriptor fd.

       The number of bytes written may be less than  count  if,	 for  example,
       there  is  insufficient space on	the underlying physical	medium,	or the
       RLIMIT_FSIZE resource limit is encountered (see setrlimit(2)),  or  the
       call was	interrupted by a signal	handler	after having written less than
       count bytes.  (See also pipe(7).)

       For a seekable file (i.e., one to which lseek(2)	may  be	 applied,  for
       example,	 a  regular file) writing takes	place at the current file off-
       set, and	the file offset	is incremented by the number of	bytes actually
       written.	  If  the file was open(2)ed with O_APPEND, the	file offset is
       first set to the	end of the file	before writing.	 The adjustment	of the
       file offset and the write operation are performed as an atomic step.

       POSIX  requires	that  a	 read(2)  which	can be proved to occur after a
       write() has returned returns the	new data.  Note	that not all file sys-
       tems are	POSIX conforming.

RETURN VALUE
       On  success,  the  number  of bytes written is returned (zero indicates
       nothing was written).  On error,	-1 is returned,	and errno is  set  ap-
       propriately.

       If  count is zero and fd	refers to a regular file, then write() may re-
       turn a failure status if	one of the errors below	is  detected.	If  no
       errors  are  detected, 0	will be	returned without causing any other ef-
       fect.  If count is zero and fd refers to	a file other  than  a  regular
       file, the results are not specified.

ERRORS
       EAGAIN The  file	descriptor fd refers to	a file other than a socket and
	      has been marked nonblocking (O_NONBLOCK),	and  the  write	 would
	      block.

       EAGAIN or EWOULDBLOCK
	      The  file	 descriptor  fd	refers to a socket and has been	marked
	      nonblocking   (O_NONBLOCK),   and	  the	write	would	block.
	      POSIX.1-2001  allows  either error to be returned	for this case,
	      and does not require these constants to have the same value,  so
	      a	portable application should check for both possibilities.

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

       EDESTADDRREQ
	      fd  refers to a datagram socket for which	a peer address has not
	      been set using connect(2).

       EDQUOT The user's quota of disk blocks on the  file  system  containing
	      the file referred	to by fd has been exhausted.

       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's 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; see signal(7).

       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 ad-
	      dress 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.

       If a write() is interrupted by a	signal handler before  any  bytes  are
       written,	then the call fails with the error EINTR; if it	is interrupted
       after at	least one byte has been	written, the call  succeeds,  and  re-
       turns the number	of bytes written.

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

COLOPHON
       This page is part of release 3.53 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/.

Linux				  2013-01-27			      WRITE(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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