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

       sysctl - read/write system parameters

       #include <unistd.h>
       #include <linux/sysctl.h>

       int _sysctl(struct __sysctl_args *args);

       Note: There is no glibc wrapper for this system call; see NOTES.

       Do not use this system call!  See NOTES.

       The  _sysctl()  call reads and/or writes kernel parameters.  For example, the hostname, or
       the maximum number of open files.  The argument has the form

	   struct __sysctl_args {
	       int    *name;	/* integer vector describing variable */
	       int     nlen;	/* length of this vector */
	       void   *oldval;	/* 0 or address where to store old value */
	       size_t *oldlenp; /* available room for old value,
				   overwritten by actual size of old value */
	       void   *newval;	/* 0 or address of new value */
	       size_t  newlen;	/* size of new value */

       This call does a search in a tree structure, possibly resembling a  directory  tree  under
       /proc/sys,  and	if  the requested item is found calls some appropriate routine to read or
       modify the value.

       Upon successful completion, _sysctl() returns 0.  Otherwise, a value of -1 is returned and
       errno is set to indicate the error.

       EFAULT The invocation asked for the previous value by setting oldval non-NULL, but allowed
	      zero room in oldlenp.

	      name was not found.

	      No search permission for one of the encountered "directories", or no  read  permis-
	      sion where oldval was nonzero, or no write permission where newval was nonzero.

       This  call  is Linux-specific, and should not be used in programs intended to be portable.
       A sysctl() call has been present in Linux since version 1.3.57.	It originated in  4.4BSD.
       Only  Linux  has  the /proc/sys mirror, and the object naming schemes differ between Linux
       and 4.4BSD, but the declaration of the sysctl() function is the same in both.

       Glibc does not provide a wrapper for this system  call;	call  it  using  syscall(2).   Or
       rather...   don't call it: use of this system call has long been discouraged, and it is so
       unloved that it is likely to disappear in a future kernel version.   Since  Linux  2.6.24,
       uses  of  this system call result in warnings in the kernel log.  Remove it from your pro-
       grams now; use the /proc/sys interface instead.

       This  system  call  is  available  only	if  the  kernel  was  configured  with	the  CON-
       FIG_SYSCTL_SYSCALL option.

       The  object  names  vary  between  kernel  versions, making this system call worthless for

       Not all available objects are properly documented.

       It is not yet possible to change operating system by writing to /proc/sys/kernel/ostype.

       #define _GNU_SOURCE
       #include <unistd.h>
       #include <sys/syscall.h>
       #include <string.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <linux/sysctl.h>

       int _sysctl(struct __sysctl_args *args );

       #define OSNAMESZ 100

	   struct __sysctl_args args;
	   char osname[OSNAMESZ];
	   size_t osnamelth;
	   int name[] = { CTL_KERN, KERN_OSTYPE };

	   memset(&args, 0, sizeof(struct __sysctl_args));
	   args.name = name;
	   args.nlen = sizeof(name)/sizeof(name[0]);
	   args.oldval = osname;
	   args.oldlenp = &osnamelth;

	   osnamelth = sizeof(osname);

	   if (syscall(SYS__sysctl, &args) == -1) {
	   printf("This machine is running %*s\n", osnamelth, osname);


       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

Linux					    2012-12-22					SYSCTL(2)
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