Re: swapping partitions including /

[Wichert Akkerman <wichert@cistron.nl>]

Previously Robert van der Meulen wrote:
> For the swapping part, you can use 'pivot_root', in the newer util-linux
> distributions. As far as i know, pivot_root is not in the debian version
> yet.

It has been added in version 2.11b-2. For those of you running testing
or stable I've attached a little pivot_root implementation I wrote
for personal use a while ago.

> A 'pivot_root . /tmp', when executed in /tmp will leave you with a /dev/sda5
> on /tmp, and /dev/sda9 on /.

More importantly, it will also change the cwd for processes that had cwd
set to root to the new root so you can safely unmount it.

> I use this to mount a reiserfs root-filesystem on an lvm volume. 

Same here :)

Wichert.

-- 
  _________________________________________________________________
 /       Nothing is fool-proof to a sufficiently talented fool     \
| wichert@cistron.nl                  http://www.liacs.nl/~wichert/ |
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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/syscall.h>

void usage() {
	fprintf(stderr,
		"Usage:\n"
		"  pivotroot <newroot> <oldroot>\n"
		"\n"
		"This will make <newroot> the new root filesystem and remount\n"
		"the old one at <oldroot>.\n");
}

int main(int argc, char** argv) {
	int	res;

	if (argc!=3) {
		fprintf(stderr, "Invalid number of arguments\n");
		usage();
		exit(1);
	}

	if ((res=syscall(SYS_pivot_root, argv[1], argv[2]))==-1) {
		perror("Error pivoting root");
		exit(2);
	} else if (res!=0) {
		fprintf(stderr, "pivot_root failed with return code %d\n", res);
		exit(3);
	}
	
	return 0;
}