View Source: _sysctl(2) - Waikato Linux Users Group

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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


#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


proc(5)
----

One page links to _sysctl(2):

syscalls(2)

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Last edited on Tuesday, June 4, 2002 12:23:38 am by "perry"

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