* Re: [gentoo-amd64] chroot howto?
2005-07-13 9:03 [gentoo-amd64] chroot howto? Peter Humphrey
@ 2005-07-13 10:05 ` Barry.SCHWARTZ
2005-07-13 10:55 ` Peter Humphrey
0 siblings, 1 reply; 3+ messages in thread
From: Barry.SCHWARTZ @ 2005-07-13 10:05 UTC (permalink / raw
To: gentoo-amd64
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Peter Humphrey <prh@gotadsl.co.uk> wrote:
> I unpacked an x86 stage 3, and set up hosts, networks and users as
> instructed, but when I tried "linux32 chroot /mnt/gentoo32 /bin/bash" I
> got a permission-refused error on /bin/bash. (I tried both with and
> without --login; it made no difference.)
Did you do this as root?
> So I unpacked a portage
> snapshot, rebooted from the installation CD and tried again. I could
> then chroot. I reasoned that /bin/bash could not be executed because
> there was no 32-bit kernel, so I emerged and compiled gentoo-sources in
> /mnt/gentoo32. After that I could chroot from the installed system.
You don't need a 32-bit kernel. For a few things it can be convenient
to have kernel sources present, but I don't remember what things those
are. Cross that bridge if you come to it.
> But how much more of a Gentoo system do I need to build in the chroot
> jail? Emerge --sync? Emerge system? I have /mnt/tmp bound to
> /mnt/gentoo32/mnt/tmp, and /mnt/home, /mnt/boot, /mnt/usr/share and
> /mnt/usr/portage/distfiles bound similarly. Do I need to env-update
> whenever I chroot? What difference is there between chroot with and
> without --login, apart from sourcing /etc/profile etc?
I set up my own init script that uses 'mount --bind' to mount and
unmount things that you need inside the chroot. So that happens at
initialization.
As far as getting into the chroot, if I am root I do it with a Perl script:
===========================================
#!/usr/bin/perl -wT
$root_32bit = "/gentoo32"; # The root directory of the 32-bit environment.
$ENV{PATH} = '/bin:/usr/bin';
delete @ENV{'IFS', 'CDPATH', 'ENV', 'BASH_ENV'};
$#ARGV == -1 or die "$0: Does not accept arguments\n";
# su to oneself. Non-root users may be asked for their password.
# (We require that the user name begin with an alphabetic character
# and consist only of alphanumeric characters.)
$user = getpwuid($<);
$user =~ /^([[:alpha:]][[:alnum:]]*)$/
or die "$0: \"$user\" doesn't look like a user name to me\n";
$user = $1;
exec "linux32", "chroot", "$root_32bit", "su", "-", "$user";
die "$0: $!\n";
===========================================
If I am non-root I do it with a simple suid root C program that is
adapted from linux32.
===========================================
/* $Id: l32.c,v 1.3 2004/08/18 05:09:30 trashman Exp $ */
#include <linux/personality.h>
#undef personality
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <limits.h>
long int personality(unsigned long int persona);
/* Restrict address space to 3 GB, for the sake of buggy Java. */
const unsigned long int default_personality = PER_LINUX32_3GB;
const char *const gentoo32 = "/gentoo32";
int main(int argc, char *argv[], char *envp[] __attribute__((unused)))
{
int result;
long int long_result;
unsigned long int pers;
char *cwd;
if (argc < 2) {
fprintf(stderr, "Usage: %s COMMAND [ARG]...\n", argv[0]);
exit(1);
}
pers = default_personality;
cwd = getcwd(NULL, 0); /* Linux-specific: allocate as many
* bytes as necessary. */
if (cwd == NULL) {
fprintf(stderr, "Can't allocate necessary space: %s\n", strerror(errno));
exit(1);
}
long_result = personality(pers);
if (long_result == -1) {
fprintf(stderr, "Can't set personality %lx: %s\n", pers, strerror(errno));
exit(1);
}
result = chroot(gentoo32);
if (result != 0) {
fprintf(stderr, "Can't chroot(%s): %s\n", gentoo32, strerror(errno));
exit(1);
}
/* Drop root privileges. */
result = setuid(getuid());
if (result != 0) {
fprintf(stderr, "Can't suid(%d): %s\n", getuid(), strerror(errno));
exit(1);
}
/* Make sure we are inside the chroot. */
result = chdir("/");
if (result != 0) {
fprintf(stderr, "Can't chdir(%s) within the chroot: %s\n",
gentoo32, strerror(errno));
exit(1);
}
/* Change into the chroot's equivalent of the current working
* directory. */
result = chdir(cwd);
if (result != 0) {
fprintf(stderr, "Can't chdir(%s) within the chroot: %s\n",
cwd, strerror(errno));
exit(1);
}
free(cwd);
execvp(argv[1], argv + 1);
abort(); /* We shouldn't get here. */
}
===========================================
'l32 zsh --login' gets me a 32-bit shell.
I maintain my chroot as practically another whole system. That's
wasteful but makes some things a lot easier -- even maintenance is
easier with all that waste, because you are letting portage 'think'
for you about what it needs to install.
I used to also run stuff like sshd inside the chroot, but don't
anymore, and I think you can ignore that.
--
Barry.SCHWARTZ@chemoelectric.org http://www.chemoelectric.org
Esperantistoj rajtas skribi al Barijo.SXVARCO@chemoelectric.org
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