#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int foo(void);
int main(int argc, char **argv)
{
	uid_t		uid;

	uid=getuid();

	foo();

	/* uid=root */
	if (-1 == setuid(0))
		perror("setuid(0)");
	else
		foo();

	/* return to uid, but still being able to get back to root */
	if (-1 == setuid(uid))
		perror("setuid(uid)");
	else
		foo();

	/* drop privileges */
	if (-1 == seteuid(uid))
		perror("seteuid(uid)");
	else
		foo();

	/* this will fail */
	if (-1 == setuid(0))
		perror("setuid(0)");
	else
		foo();

}


int foo(void)
{
#ifndef BS
#define BS  512
#endif

	FILE        *i;
	char        buffer[BS];
	size_t      n;

/*	if ( NULL == ( i = popen( "/bin/id -a", "r")))*/
	if ( NULL == ( i = popen( "/usr/xpg4/bin/id", "r")))
	{
		perror("popen");
		return 1;
	}
	while ( 0 != ( n = fread( buffer, 1, BS, i )))
		fwrite( buffer, 1, n, stdout );

	pclose(i);
}