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READ(2)			   Linux Programmer's Manual		       READ(2)

NAME
       read - read from	a file descriptor

SYNOPSIS
       #include	<unistd.h>

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

DESCRIPTION
       read()  attempts	to read	up to count bytes from file descriptor fd into
       the buffer starting at buf.

       If count	is zero, read()	returns	zero and has  no  other	 results.   If
       count is	greater	than SSIZE_MAX,	the result is unspecified.

RETURN VALUE
       On success, the number of bytes read is returned	(zero indicates	end of
       file), and the file position is advanced	by this	number.	 It is not  an
       error  if  this	number	is smaller than	the number of bytes requested;
       this may	happen for example because fewer bytes are actually  available
       right  now  (maybe  because we were close to end-of-file, or because we
       are reading from	a pipe,	or from	a terminal),  or  because  read()  was
       interrupted  by	a  signal.  On error, -1 is returned, and errno	is set
       appropriately. In this case it is left  unspecified  whether  the  file
       position	(if any) changes.

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

       EAGAIN Non-blocking  I/O	has been selected using	O_NONBLOCK and no data
	      was immediately available	for reading.

       EIO    I/O error. This will happen for example when the process is in a
	      background  process  group,  tries  to read from its controlling
	      tty, and either it  is  ignoring	or  blocking  SIGTTIN  or  its
	      process  group  is  orphaned.  It	may also occur when there is a
	      low-level	I/O error while	reading	from a disk or tape.

       EISDIR fd refers	to a directory.

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

       EINVAL fd is attached to	an object which	is unsuitable for reading.

       EFAULT buf is outside your accessible address space.

       Other errors may	occur, depending on the	object connected to fd.	 POSIX
       allows  a read that is interrupted after	reading	some data to return -1
       (with errno set to EINTR) or to return  the  number  of	bytes  already
       read.

CONFORMING TO
       SVr4, SVID, AT&T, POSIX,	X/OPEN,	BSD 4.3

RESTRICTIONS
       On NFS file systems, reading small amounts of data will only update the
       time stamp the first time, subsequent calls may not  do	so.   This  is
       caused  by  client  side	attribute caching, because most	if not all NFS
       clients leave atime updates to the server and client side reads	satis-
       fied from the client's cache will not cause atime updates on the	server
       as there	are no server side reads.  UNIX	semantics can be  obtained  by
       disabling  client  side	attribute caching, but in most situations this
       will substantially increase server load and decrease performance.

       Many filesystems	and disks were considered to be	fast enough  that  the
       implementation of O_NONBLOCK was	deemed unneccesary. So,	O_NONBLOCK may
       not be available	on files and/or	disks.

SEE ALSO
       close(2),  fcntl(2),  ioctl(2),	lseek(2),   readdir(2),	  readlink(2),
       select(2), write(2), fread(3), readv(3)

Linux 2.0.32			  1997-07-12			       READ(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | RESTRICTIONS | SEE ALSO

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