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closefrom(3C)		 Standard C Library Functions		 closefrom(3C)

NAME
       closefrom, fdwalk - close or iterate over open file descriptors

SYNOPSIS
       #include	<stdlib.h>

       void closefrom(int  lowfd);

       int fdwalk(int (*func)(void *, int), void *cd);

DESCRIPTION
       The  closefrom()	 function  calls close(2) on all open file descriptors
       greater than or equal to	lowfd.

       The effect of closefrom(lowfd) is the same as the code

       #include	<sys/resource.h>
       struct rlimit rl;
       int i;

       getrlimit(RLIMIT_NOFILE,	&rl);
       for (i =	lowfd; i < rl.rlim_max;	i++)
	    (void) close(i);

       except that close() is called only on file descriptors that  are	 actu-
       ally  open, not on every	possible file descriptor greater than or equal
       to lowfd, and close() is	also  called  on  any  open  file  descriptors
       greater than or equal to	rl.rlim_max (and lowfd), should	any exist.

       The fdwalk() function first makes a list	of all currently open file de-
       scriptors. Then for each	file descriptor	in  the	 list,	it  calls  the
       user-defined  function,	func(cd,  fd),	passing	 it the	pointer	to the
       callback	data, cd, and the value	of the file descriptor from the	 list,
       fd.   The  list is processed in file descriptor value order, lowest nu-
       meric value first.

       If func() returns a non-zero value, the iteration over the list is ter-
       minated	and  fdwalk()  returns	the non-zero value returned by func().
       Otherwise, fdwalk() returns 0 after having called func()	for every file
       descriptor in the list.

       The  fdwalk()  function	can  be	used for fine-grained control over the
       closing of file descriptors.  For example, the closefrom() function can
       be implemented as:

       static int
       close_func(void *lowfdp,	int fd)
       {
	    if (fd >= *(int *)lowfdp)
		 (void)	close(fd);
	    return (0);
       }

       void
       closefrom(int lowfd)
       {
	    (void) fdwalk(close_func, &lowfd);
       }

       The  fdwalk()  function	can  then  be used to count the	number of open
       files in	the process.

RETURN VALUES
       No return value is defined for closefrom(). If close() fails for	any of
       the  open  file descriptors, the	error is ignored and the file descrip-
       tors whose close() operation failed might remain	open  on  return  from
       closefrom().

       The  fdwalk() function returns the return value of the last call	to the
       callback	function func(), or 0 if  func()  is  never  called  (no  open
       files).

ERRORS
       No  errors  are	defined. The closefrom() and fdwalk() functions	do not
       set errno but errno can be set by close() or by another function	called
       by the callback function, func().

FILES
	      /proc/self/fd
		    directory (list of open files)

USAGE
       The  act	 of closing all	open file descriptors should be	performed only
       as the first action of a	daemon process.	 Closing file descriptors that
       are  in	use  elsewhere in the current process normally leads to	disas-
       trous results.

ATTRIBUTES
       See attributes(5)  for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE	TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Unsafe			   |
       +-----------------------------+-----------------------------+

SEE ALSO
       close(2), getrlimit(2), proc(4),	attributes(5)

SunOS 5.9			  27 Apr 2000			 closefrom(3C)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | FILES | USAGE | ATTRIBUTES | SEE ALSO

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