close(2)

NAME

     close - close a file descriptor

SYNOPSIS

     #include <unistd.h>

     int close(int fildes);

DESCRIPTION

     The close() function will  deallocate  the  file  descriptor
     indicated  by  fildes.  To deallocate means to make the file
     descriptor available  for  return  by  subsequent  calls  to
     open(2)  or  other functions that allocate file descriptors.
     All outstanding record locks owned by  the  process  on  the
     file  associated  with  the  file descriptor will be removed
     (that is, unlocked).

     If close() is interrupted by a signal that is to be  caught,
     it  will  return -1 with errno set to EINTR and the state of
     fildes is unspecified.

     When all file descriptors associated with  a  pipe  or  FIFO
     special  file  are closed, any data remaining in the pipe or
     FIFO will be discarded.

     When all file  descriptors  associated  with  an  open  file
     description  have been closed the open file description will
     be freed.

     If the link count of the file is 0, when all  file  descrip-
     tors associated with the file are closed, the space occupied
     by the file will be freed and the file  will  no  longer  be
     accessible.

     If a STREAMS-based (see intro(2)) fildes is closed  and  the
     calling  process was previously registered to receive a SIG-
     POLL signal (see signal(3C)) for events associated with that
     STREAM  (see  I_SETSIG in streamio(7I)), the calling process
     will be unregistered for events associated with the  STREAM.
     The  last  close() for a STREAM causes the STREAM associated
     with fildes to be dismantled. If O_NONBLOCK and O_NDELAY are
     not  set  and  there  have  been  no  signals posted for the
     STREAM, and if there is data on the  module's  write  queue,
     close()  waits up to 15 seconds (for each module and driver)
     for any output to drain before dismantling the  STREAM.  The
     time  delay  can  be  changed  via  an  I_SETCLTIME ioctl(2)
     request (see streamio(7I)). If the  O_NONBLOCK  or  O_NDELAY
     flag  is  set,  or if there are any pending signals, close()
     does not wait for output to drain, and dismantles the STREAM
     immediately.

     If fildes is associated with one end of  a  pipe,  the  last
     close()  causes  a  hangup  to occur on the other end of the
     pipe.  In addition, if the other end of the  pipe  has  been
     named by fattach(3C), then the last close() forces the named
     end to be detached by fdetach(3C).  If the named end has  no
     open  file descriptors associated with it and gets detached,
     the STREAM associated with that end is also dismantled.

     If fildes refers to the master side of a pseudo-terminal,  a
     SIGHUP  signal  is  sent  to  the process group, if any, for
     which the slave side of the pseudo-terminal is the  control-
     ling  terminal. It is unspecified whether closing the master
     side of the pseudo-terminal flushes  all  queued  input  and
     output.

     If fildes refers  to  the  slave  side  of  a  STREAMS-based
     pseudo-terminal,  a  zero-length  message may be sent to the
     master.

     If fildes refers to a socket, close() causes the  socket  to
     be  destroyed.   If  the  socket is connection-mode, and the
     SOCK_LINGER option is set for the socket, and the socket has
     untransmitted  data,  then  close() will block for up to the
     current linger interval until all data is transmitted.

RETURN VALUES

     Upon successful completion, 0 is returned. Otherwise, -1  is
     returned and errno is set to indicate the error.

ERRORS

     The close() function will fail if:

     EBADF The fildes argument is not a valid file descriptor.

     EINTR The close() function was interrupted by a signal.

     ENOLINK
           The fildes argument is on a  remote  machine  and  the
           link to that machine is no longer active.

     ENOSPC
           There was no free space remaining on the  device  con-
           taining the file.

     The close() function may fail if:

     EIO   An I/O error occurred while reading from or writing to
           the file system.

USAGE

     An application that used the  stdio  function  fopen(3C)  to
     open a file should use the corresponding fclose(3C) function
     rather than close().

     When a UFS file system is mounted with logging enabled, file
     system  transactions  that  free blocks from files might not
     actually add those freed blocks to the  file  system's  free
     list  until  some  unspecified  time  in  the  future.  This
     behavior improves file system performance but does not  con-
     form  to the POSIX, Single UNIX Specification, SPARC Confor-
     mance Definition, System  V  Application  Binary  Interface,
     System  V Interface Definition, and X/Open Portability Guide
     Standards, which  require  that  freed  space  be  available
     immediately.  To enable standards conformance regarding file
     deletions or to address the problem of  not  being  able  to
     grow  files  on a relatively full UFS file system even after
     files  have  been  deleted,   disable   UFS   logging   (see
     mount_ufs(1M).

ATTRIBUTES

     See attributes(5) for descriptions of the  following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | MT-Level                    | Async-Signal-Safe           |
    |_____________________________|_____________________________|

SEE ALSO

     mount_ufs(1M),   intro(2),   creat(2),   dup(2),    exec(2),
     fcntl(2),    ioctl(2),    open(2)    pipe(2),   fattach(3C),
     fclose(3C),  fdetach(3C),  fopen(3C),   signal(3C),   attri-
     butes(5), signal(3HEAD), streamio(7I)