2004-11-03 13:51:07 +00:00
|
|
|
.\" Copyright (C) 1996 Andries Brouwer (aeb@cwi.nl)
|
|
|
|
.\"
|
|
|
|
.\" 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.
|
2007-04-12 22:42:49 +00:00
|
|
|
.\"
|
2004-11-03 13:51:07 +00:00
|
|
|
.\" 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.\" manual page may be incorrect or out-of-date.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.
|
2007-04-12 22:42:49 +00:00
|
|
|
.\"
|
2004-11-03 13:51:07 +00:00
|
|
|
.\" Formatted or processed versions of this manual, if unaccompanied by
|
|
|
|
.\" the source, must acknowledge the copyright and authors of this work.
|
|
|
|
.\"
|
|
|
|
.\" Written 11 April 1996 by Andries Brouwer <aeb@cwi.nl>
|
|
|
|
.\" 960412: Added comments from Stephen Tweedie
|
|
|
|
.\" Modified Tue Oct 22 22:28:41 1996 by Eric S. Raymond <esr@thyrsus.com>
|
|
|
|
.\" Modified Mon Jan 5 20:31:04 1998 by aeb.
|
|
|
|
.\"
|
2008-11-20 19:33:26 +00:00
|
|
|
.TH SYSCTL 2 2008-11-20 "Linux" "Linux Programmer's Manual"
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH NAME
|
|
|
|
sysctl \- read/write system parameters
|
|
|
|
.SH SYNOPSIS
|
2006-03-16 00:50:08 +00:00
|
|
|
.nf
|
2004-11-03 13:51:07 +00:00
|
|
|
.B #include <unistd.h>
|
2004-12-10 09:03:08 +00:00
|
|
|
.br
|
2004-11-03 13:51:07 +00:00
|
|
|
.B #include <linux/sysctl.h>
|
|
|
|
.sp
|
|
|
|
.BI "int _sysctl(struct __sysctl_args *" args );
|
2006-03-16 00:50:08 +00:00
|
|
|
.fi
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH DESCRIPTION
|
2008-11-26 02:44:53 +00:00
|
|
|
.B Do not use this system call!
|
2008-11-20 19:33:26 +00:00
|
|
|
See NOTES.
|
|
|
|
|
2004-11-03 13:51:07 +00:00
|
|
|
The
|
2005-10-19 06:54:38 +00:00
|
|
|
.BR _sysctl ()
|
2007-04-12 22:42:49 +00:00
|
|
|
call reads and/or writes kernel parameters.
|
|
|
|
For example, the hostname,
|
|
|
|
or the maximum number of open files.
|
|
|
|
The argument has the form
|
2004-11-03 13:51:07 +00:00
|
|
|
.PP
|
2007-12-19 06:57:44 +00:00
|
|
|
.in +4n
|
2004-11-03 13:51:07 +00:00
|
|
|
.nf
|
|
|
|
struct __sysctl_args {
|
2007-05-16 03:06:55 +00:00
|
|
|
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 */
|
2004-11-03 13:51:07 +00:00
|
|
|
};
|
|
|
|
.fi
|
2007-05-16 03:06:55 +00:00
|
|
|
.in
|
2004-11-03 13:51:07 +00:00
|
|
|
.PP
|
|
|
|
This call does a search in a tree structure, possibly resembling
|
|
|
|
a directory tree under
|
2005-11-02 13:55:25 +00:00
|
|
|
.IR /proc/sys ,
|
2004-11-03 13:51:07 +00:00
|
|
|
and if the requested item is found calls some appropriate routine
|
|
|
|
to read or modify the value.
|
|
|
|
.SH "RETURN VALUE"
|
|
|
|
Upon successful completion,
|
2005-10-19 06:54:38 +00:00
|
|
|
.BR _sysctl ()
|
2007-04-12 22:42:49 +00:00
|
|
|
returns 0.
|
|
|
|
Otherwise, a value of \-1 is returned and
|
2004-11-03 13:51:07 +00:00
|
|
|
.I errno
|
|
|
|
is set to indicate the error.
|
|
|
|
.SH ERRORS
|
|
|
|
.TP
|
|
|
|
.B EFAULT
|
|
|
|
The invocation asked for the previous value by setting
|
|
|
|
.I oldval
|
|
|
|
non-NULL, but allowed zero room in
|
|
|
|
.IR oldlenp .
|
|
|
|
.TP
|
|
|
|
.B ENOTDIR
|
|
|
|
.I name
|
|
|
|
was not found.
|
|
|
|
.TP
|
|
|
|
.B EPERM
|
2007-12-18 07:47:22 +00:00
|
|
|
No search permission for one of the encountered "directories",
|
2004-11-03 13:51:07 +00:00
|
|
|
or no read permission where
|
|
|
|
.I oldval
|
intro.1, time.1, adjtimex.2, capget.2, eventfd.2, fcntl.2, getrlimit.2, getsockopt.2, gettimeofday.2, intro.2, ioctl_list.2, ioperm.2, mlock.2, pivot_root.2, poll.2, prctl.2, ptrace.2, sched_setscheduler.2, select_tut.2, semget.2, sigaltstack.2, signalfd.2, sysctl.2, timer_settime.2, timerfd_create.2, wait.2, CPU_SET.3, argz_add.3, assert_perror.3, atexit.3, backtrace.3, bcmp.3, clearenv.3, ctime.3, dl_iterate_phdr.3, dlopen.3, ecvt.3, errno.3, error.3, ether_aton.3, exit.3, fenv.3, ferror.3, finite.3, flockfile.3, fnmatch.3, fpathconf.3, fpclassify.3, ftime.3, ftok.3, ftw.3, fwide.3, getaddrinfo.3, gethostbyname.3, getlogin.3, getnameinfo.3, getnetent.3, getopt.3, getprotoent.3, getrpcent.3, getservent.3, glob.3, hsearch.3, inet.3, isalpha.3, iswalnum.3, iswalpha.3, iswblank.3, iswcntrl.3, iswctype.3, iswdigit.3, iswgraph.3, iswlower.3, iswprint.3, iswpunct.3, iswspace.3, iswupper.3, iswxdigit.3, longjmp.3, lsearch.3, malloc.3, matherr.3, mblen.3, mbsinit.3, mbtowc.3, on_exit.3, printf.3, pthread_attr_init.3, pthread_attr_setaffinity_np.3, pthread_attr_setdetachstate.3, pthread_attr_setguardsize.3, pthread_attr_setinheritsched.3, pthread_attr_setschedparam.3, pthread_attr_setschedpolicy.3, pthread_attr_setscope.3, pthread_attr_setstack.3, pthread_attr_setstackaddr.3, pthread_attr_setstacksize.3, pthread_cancel.3, pthread_cleanup_push.3, pthread_equal.3, pthread_getattr_np.3, pthread_getcpuclockid.3, pthread_setaffinity_np.3, pthread_setcancelstate.3, pthread_setconcurrency.3, pthread_setschedparam.3, pthread_setschedprio.3, ptsname.3, putenv.3, putgrent.3, raise.3, rcmd.3, regex.3, rexec.3, rpc.3, rpmatch.3, rtnetlink.3, scandir.3, sem_init.3, setaliasent.3, setbuf.3, setenv.3, setjmp.3, signbit.3, stdio_ext.3, strtod.3, strtol.3, strtoul.3, system.3, termios.3, timeradd.3, tzset.3, ualarm.3, wctomb.3, xdr.3, st.4, tty_ioctl.4, core.5, elf.5, proc.5, bootparam.7, capabilities.7, icmp.7, ip.7, ipv6.7, math_error.7, mdoc.samples.7, mq_overview.7, pthreads.7, raw.7, regex.7, socket.7, tcp.7, tzselect.8: Global fix: s/non-zero/nonzero/
The tendency in English, as prescribed in style guides like
Chicago MoS, is towards removing hyphens after prefixes
like "non-" etc.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2010-01-16 16:40:55 +00:00
|
|
|
was nonzero, or no write permission where
|
2004-11-03 13:51:07 +00:00
|
|
|
.I newval
|
intro.1, time.1, adjtimex.2, capget.2, eventfd.2, fcntl.2, getrlimit.2, getsockopt.2, gettimeofday.2, intro.2, ioctl_list.2, ioperm.2, mlock.2, pivot_root.2, poll.2, prctl.2, ptrace.2, sched_setscheduler.2, select_tut.2, semget.2, sigaltstack.2, signalfd.2, sysctl.2, timer_settime.2, timerfd_create.2, wait.2, CPU_SET.3, argz_add.3, assert_perror.3, atexit.3, backtrace.3, bcmp.3, clearenv.3, ctime.3, dl_iterate_phdr.3, dlopen.3, ecvt.3, errno.3, error.3, ether_aton.3, exit.3, fenv.3, ferror.3, finite.3, flockfile.3, fnmatch.3, fpathconf.3, fpclassify.3, ftime.3, ftok.3, ftw.3, fwide.3, getaddrinfo.3, gethostbyname.3, getlogin.3, getnameinfo.3, getnetent.3, getopt.3, getprotoent.3, getrpcent.3, getservent.3, glob.3, hsearch.3, inet.3, isalpha.3, iswalnum.3, iswalpha.3, iswblank.3, iswcntrl.3, iswctype.3, iswdigit.3, iswgraph.3, iswlower.3, iswprint.3, iswpunct.3, iswspace.3, iswupper.3, iswxdigit.3, longjmp.3, lsearch.3, malloc.3, matherr.3, mblen.3, mbsinit.3, mbtowc.3, on_exit.3, printf.3, pthread_attr_init.3, pthread_attr_setaffinity_np.3, pthread_attr_setdetachstate.3, pthread_attr_setguardsize.3, pthread_attr_setinheritsched.3, pthread_attr_setschedparam.3, pthread_attr_setschedpolicy.3, pthread_attr_setscope.3, pthread_attr_setstack.3, pthread_attr_setstackaddr.3, pthread_attr_setstacksize.3, pthread_cancel.3, pthread_cleanup_push.3, pthread_equal.3, pthread_getattr_np.3, pthread_getcpuclockid.3, pthread_setaffinity_np.3, pthread_setcancelstate.3, pthread_setconcurrency.3, pthread_setschedparam.3, pthread_setschedprio.3, ptsname.3, putenv.3, putgrent.3, raise.3, rcmd.3, regex.3, rexec.3, rpc.3, rpmatch.3, rtnetlink.3, scandir.3, sem_init.3, setaliasent.3, setbuf.3, setenv.3, setjmp.3, signbit.3, stdio_ext.3, strtod.3, strtol.3, strtoul.3, system.3, termios.3, timeradd.3, tzset.3, ualarm.3, wctomb.3, xdr.3, st.4, tty_ioctl.4, core.5, elf.5, proc.5, bootparam.7, capabilities.7, icmp.7, ip.7, ipv6.7, math_error.7, mdoc.samples.7, mq_overview.7, pthreads.7, raw.7, regex.7, socket.7, tcp.7, tzselect.8: Global fix: s/non-zero/nonzero/
The tendency in English, as prescribed in style guides like
Chicago MoS, is towards removing hyphens after prefixes
like "non-" etc.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2010-01-16 16:40:55 +00:00
|
|
|
was nonzero.
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH "CONFORMING TO"
|
2007-12-25 21:28:09 +00:00
|
|
|
This call is Linux-specific, and should not be used in programs
|
2004-11-03 13:51:07 +00:00
|
|
|
intended to be portable.
|
|
|
|
A
|
2005-10-19 06:54:38 +00:00
|
|
|
.BR sysctl ()
|
2007-04-12 22:42:49 +00:00
|
|
|
call has been present in Linux since version 1.3.57.
|
|
|
|
It originated in
|
|
|
|
4.4BSD.
|
|
|
|
Only Linux has the
|
2004-11-03 13:51:07 +00:00
|
|
|
.I /proc/sys
|
2005-07-18 15:05:56 +00:00
|
|
|
mirror, and the object naming schemes differ between Linux and 4.4BSD,
|
2004-11-03 13:51:07 +00:00
|
|
|
but the declaration of the
|
2007-11-24 10:10:39 +00:00
|
|
|
.BR sysctl ()
|
2004-11-03 13:51:07 +00:00
|
|
|
function is the same in both.
|
2007-06-14 06:31:39 +00:00
|
|
|
.SH NOTES
|
|
|
|
Glibc does not provide a wrapper for this system call; call it using
|
|
|
|
.BR syscall (2).
|
2007-09-13 17:41:38 +00:00
|
|
|
|
|
|
|
Or rather... don't call it:
|
|
|
|
use of this system call has long been discouraged,
|
|
|
|
and it is so unloved that
|
2007-12-22 16:46:37 +00:00
|
|
|
\fBit is likely to disappear in a future kernel version\fP.
|
2007-09-19 21:42:14 +00:00
|
|
|
.\" See http://lwn.net/Articles/247243/
|
2007-09-13 17:41:38 +00:00
|
|
|
Remove it from your programs now; use the
|
2004-11-03 13:51:07 +00:00
|
|
|
.I /proc/sys
|
|
|
|
interface instead.
|
2007-09-13 17:41:38 +00:00
|
|
|
.SH BUGS
|
|
|
|
The object names vary between kernel versions,
|
|
|
|
making this system call worthless for applications.
|
2007-05-16 03:05:19 +00:00
|
|
|
.PP
|
2004-11-03 13:51:07 +00:00
|
|
|
Not all available objects are properly documented.
|
2007-05-16 03:05:19 +00:00
|
|
|
.PP
|
2004-11-03 13:51:07 +00:00
|
|
|
It is not yet possible to change operating system by writing to
|
|
|
|
.IR /proc/sys/kernel/ostype .
|
2007-05-19 04:30:20 +00:00
|
|
|
.SH EXAMPLE
|
|
|
|
.nf
|
2007-05-26 15:22:28 +00:00
|
|
|
#define _GNU_SOURCE
|
|
|
|
#include <unistd.h>
|
|
|
|
#include <sys/syscall.h>
|
|
|
|
#include <string.h>
|
|
|
|
#include <stdio.h>
|
|
|
|
#include <stdlib.h>
|
2007-05-19 04:30:20 +00:00
|
|
|
#include <linux/sysctl.h>
|
|
|
|
|
2007-05-26 15:22:28 +00:00
|
|
|
int _sysctl(struct __sysctl_args *args );
|
2007-05-19 04:30:20 +00:00
|
|
|
|
|
|
|
#define OSNAMESZ 100
|
|
|
|
|
|
|
|
int
|
|
|
|
main(void)
|
|
|
|
{
|
2007-05-26 15:22:28 +00:00
|
|
|
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;
|
2007-06-21 22:55:04 +00:00
|
|
|
|
2007-05-19 04:30:20 +00:00
|
|
|
osnamelth = sizeof(osname);
|
2007-06-21 22:55:04 +00:00
|
|
|
|
2007-06-20 21:39:45 +00:00
|
|
|
if (syscall(SYS__sysctl, &args) == \-1) {
|
2007-05-26 15:22:28 +00:00
|
|
|
perror("_sysctl");
|
|
|
|
exit(EXIT_FAILURE);
|
|
|
|
}
|
2007-05-28 15:52:03 +00:00
|
|
|
printf("This machine is running %*s\\n", osnamelth, osname);
|
2007-05-19 04:30:20 +00:00
|
|
|
exit(EXIT_SUCCESS);
|
|
|
|
}
|
|
|
|
.fi
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH "SEE ALSO"
|
|
|
|
.BR proc (5)
|