From: Enrico Scholz (enrico.scholz_at_informatik.tu-chemnitz.de)
Date: Fri 06 May 2005 - 20:04:18 BST

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psg_at_cooldog.com ("Paul S. Gumerman") writes:

> Is there anywhere to be found an explanation of how package management
> works with the new util-vserver system?

I would suggest (for Fedora based systems):

1. create your own yum or apt repository by:
   a) copy all the shipped RPMs somewhere into your harddrive; e.g.
      | D=/srv/data/mirror/fedora/core
      | rsync -a /media/cdrom/Fedora/RPMS/ $D/3/i386
   b) ditto for updates (e.g. execute a daily cronjob mirroring the
      updates directory)
      | rsync -a http://..../ $D/3-updates/i386
   c) create the yum filesystem structure there:
      | mkdir -p $D/.yum/3/i386/{base,updates}
      | ln -s ../../../../3/i386 $D/.yum/i386/base/RPMS
      | ln -s ../../../../3-updates/i386 $D/.yum/i386/updates/RPMS
   d) create the repo there
      | createrepo $D/.yum/i386/base
      | createrepo $D/.yum/i386/updates

   e) ... similarly for apt ... ;)

2. register them as the repository for FC3
   a) | mkdir -p /etc/vservers/.distributions/fc3/yum.repos.d
   b) | cat <<EOF >/etc/vservers/.distributions/fc3/yum.repos.d/fc3.repo
[base]
name=Fedora Core $releasever - $basearch - Base
baseurl=file:///srv/data/mirror/fedora/core/.yum/3/$basearch/base
enabled=1
gpgcheck=1
EOF
   c) | cat <<EOF >/etc/vservers/.distributions/fc3/yum.repos.d/fc3-updates.repo
[updates]
name=Fedora Core $releasever - $basearch - Updates
baseurl=file:///srv/data/mirror/fedora/core/.yum/3/$basearch/updates
enabled=1
gpgcheck=0
EOF

   To be more flexible, I strongly suggest to create an ftp or http
   vserver which provides the tree at $D. But for bootstrapping, the
   file:// based repo is ok.

   You will have to use hardcoded version strings ('3') instead of the
   flexible '$releasever' in the URL; yum does not provide any way to
   override this at runtime. Feel free to write a bugreport for yum ;)

3. Now, you can begin to create vservers

   | # vserver test build -m yum -- -d fc3

   and install additional packages; e.g.

   | # vyum test -- install cfengine
   | # vrpm test -- -q cfengine

4. When you really need it, you can internalize the packagemanagement
   with

   | # vserver test pkgmgmt internalize

   But most of my vservers do not have internal packagemanagement; it
   adds additional dependencies and my vservers shall be minimal.

   Current (0.30.207) util-vserver version has a bug in the
   internalization process: you have to remove the '%_rpmdb' macro
   manually from /etc/rpm/macros in the vserver. Currently, yum
   configuration is not copied neither so you have to do this manually.

> What I am particularly curious about is the usage of the various
> .rpmdb directories inside each vserver,

It is used to mount the rpm database in a secure way. "Secure" means
that programs running in the vserver can not modify it. This is solved
by

1. creating a new namespace before real rpm operations
2. bind-mounting '/vservers/.pkg/.../rpm/state' to /vservers/.../.rpmdb;
   this operation is done in a secure way
3. creating a new namespace and unmounting /.rpmdb before scripts are
   executed
4. changing the context before executing scripts

The /.rpmdb mountpoint has to be in the toplevel directory; else when it
would be e.g. /var/lib/rpm, an attacker within the vserver could create a
/var/lib -> /var/foo symlink and place a malicious rpm database (e.g. a
such one which causes buffer overflows) into /var/foo/rpm.

There are some tricks like mounting the new database into the host also
which workarounds some bugs in rpm.

> and the .pkg directory structure under the vdirbase, and how they are
> related.

Program-depending directories are directly placed under /vservers/.pkg
(e.g. 'rpm', 'apt' or 'yum'). Then, there are case depending directories
like 'rpm/etc' which corresponds to '/etc/rpm', or 'rpm/state' which
holds the rpm database, or 'yum/etc' for the configuration, or ...

An important file is the the generated rpm-macros file (rpm/etc/macros):
it contains both the %_rpmdb macro mentioned above and a line like:

| %_netsharedpath /dev:/etc/rc.d/init.d/halt:/sbin/new-kernel-pkg:/usr/bin/rhgb-client

This is needed to prevent installation of certain files (e.g. the
default '/etc/rc.d/init.d/halt' causes problems on vserver shutdown,
or '/sbin/new-kernel-pkg' makes installation of kernel package fail).

Enrico

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