From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <0c1a28eaa3675826962acdf5f048a410@plan9.bell-labs.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] as.c -- invoke things as another user.
From: "Russ Cox" <rsc@plan9.bell-labs.com>
In-Reply-To: <200301202115.h0KLFhw19151@augusta.math.psu.edu>
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Date: Mon, 20 Jan 2003 16:20:58 -0500
Topicbox-Message-UUID: 44634d3c-eacb-11e9-9e20-41e7f4b1d025

The only user name you can write to #c is none, so
a few of us use a short C program called none:

#include <u.h>
#include <libc.h>
#include <auth.h>

void
main(int argc, char *argv[])
{
	char cmd[8192];
	int fd;

	argv0 = argv[0];
	if (rfork(RFENVG|RFNAMEG) < 0)
		sysfatal("can't make new pgrp");

	fd = open("#c/user", OWRITE);
	if (fd < 0)
		sysfatal("can't open #c/user");
	if (write(fd, "none", strlen("none")) < 0)
		sysfatal("can't become none");
	close(fd);

	if (newns("none", nil) < 0)
		sysfatal("can't build namespace");

	if (argc > 1) {
		strcpy(cmd, argv[1]);
		exec(cmd, &argv[1]);
		if (strncmp(cmd, "/", 1) != 0
		&& strncmp(cmd, "./", 2) != 0
		&& strncmp(cmd, "../", 3) != 0) {
			sprint(cmd, "/bin/%s", argv[1]);
			exec(cmd, &argv[1]);
		}
	} else {
		strcpy(cmd, "/bin/rc");
		execl(cmd, cmd, nil);
	}
	sysfatal(cmd);
}