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 actually 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 descriptors. 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 numeric value first.

       If func() returns a non-zero value, the iteration over the list is terminated 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
       descriptors 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 disastrous 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 5.10							    27 Apr 2000 						     closefrom(3C)