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From: Paul S. Gumerman (psg_at_cooldog.com)
Date: Fri 06 May 2005 - 21:42:11 BST


Enrico,

Thanks so much for the explanations. And the detailed info on setting
up local repositories was an extra bonus!

It appears that I now have a vserver with properly functioning package
management with CentOS4.

Yet another question ... would you recommend using vunify or vhashify ?
I understand that vhashify will work on files that are not part of any
package, but I assume that there must be a "cost" or downside to using
the extra capability.

Regards,
  Paul (and thanks again!)

Enrico Scholz wrote:

>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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