sysctl — read/write system parameters
#include <unistd.h> #include <linux/sysctl.h>
int
_sysctl( |
struct __sysctl_args *args); |
This system call no longer exists on current kernels! 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;int nlen;void * oldval;size_t * oldlenp;
overwritten by actual size of old value */void * newval;size_t newlen;};
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.
No search permission for one of the encountered
"directories", or no read permission where oldval was nonzero, or no
write permission where newval was nonzero.
The invocation asked for the previous value by
setting oldval
non-NULL, but allowed zero room in oldlenp.
name was not
found.
This system call first appeared in Linux 1.3.57. It was removed in Linux 5.5; glibc support was removed in version 2.32.
This call is Linux-specific, and should not be used in
programs intended to be portable. 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.
Use of this system call was long discouraged: since Linux
2.6.24, uses of this system call result in warnings in the
kernel log, and in Linux 5.5, the system call was finally
removed. Use the /proc/sys
interface instead.
Note that on older kernels where this system call still
exists, it is available only if the kernel was configured
with the CONFIG_SYSCTL_SYSCALL
option. Furthermore, glibc does not provide a wrapper for
this system call, necessitating the use of syscall(2).
The object names vary between kernel versions, making this system call worthless for applications.
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
int
main(void)
{
struct __sysctl_args args;
char osname[OSNAMESZ];
size_t osnamelth;
int name[] = { CTL_KERN, KERN_OSTYPE };
memset(&args, 0, sizeof(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) {
perror("_sysctl");
exit(EXIT_FAILURE);
}
printf("This machine is running %*s\n", osnamelth, osname);
exit(EXIT_SUCCESS);
}
This page is part of release 5.11 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Copyright (C) 1996 Andries Brouwer (aebcwi.nl) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END Written 11 April 1996 by Andries Brouwer <aebcwi.nl> 960412: Added comments from Stephen Tweedie Modified Tue Oct 22 22:28:41 1996 by Eric S. Raymond <esrthyrsus.com> Modified Mon Jan 5 20:31:04 1998 by aeb. |