SYSCTL

SYSCTL

NAME SYNOPSIS DESCRIPTION EXAMPLE RETURN VALUE ERRORS CONFORMING TO BUGS SEE ALSO

NAME

sysctl - read/write system parameters

SYNOPSIS

#include

#include

#include

_syscall1(int, _sysctl, struct sysctl_args *, args);__

int _sysctl(struct sysctl_args *args);

__!!DESCRIPTION

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.

EXAMPLE

1. include

RETURN VALUE

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

ERRORS

ENOTDIR

name was not found.

EPERM

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.

EFAULT

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

CONFORMING TO

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 BSD 4.4, but the declaration of the sysctl(2) function is the same in both.

BUGS

The object names vary between kernel versions. THIS MAKES THIS SYSTEM CALL WORTHLESS FOR APPLICATIONS. Use the /proc/sys interface instead. Not all available objects are properly documented. It is not yet possible to change operating system by writing to /proc/sys/kernel/ostype.

SEE ALSO

Sysctl

proc(5)