#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.
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.
This system call is available only if the kernel was configured with the CONFIG_SYSCTL_SYSCALL option.
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(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) {
perror("_sysctl");
exit(EXIT_FAILURE);
}
printf("This machine is running %*s\n", osnamelth, osname);
exit(EXIT_SUCCESS);
}