LVM boot with dracut and OpenRC on Gentoo

 Admin Hints, Gentoo, GNU/Linux  No Responses »
Oct 312012
 

As a Linux enthusiast and Gentoo user I was always looking for the perfect boot experience. While I managed to boot my kernel with EFI and grub 2 (as described in my wiki), I still had some troubles with OpenRC playing nice with my LVM-only setup initialized by dracut. Tonight I finally figured out the missing configuration pieces to shut up all warnings on system init.

Initial situation
All my Linux partitions are stored in a single LVM volume group, to stay as flexible as possible:

merkur ~ # lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
[...]
└─sda5 8:5 0 49.5G 0 part
├─vg_merkur-slash (dm-0) 253:0 0 2.5G 0 lvm /
├─vg_merkur-boot (dm-1) 253:1 0 200M 0 lvm /boot
├─vg_merkur-tmp (dm-2) 253:2 0 6G 0 lvm /tmp
├─vg_merkur-swap (dm-3) 253:3 0 4G 0 lvm [SWAP]
├─vg_merkur-var (dm-4) 253:4 0 4G 0 lvm /var
├─vg_merkur-usr (dm-5) 253:5 0 12.8G 0 lvm /usr
└─vg_merkur-opt (dm-6) 253:6 0 8G 0 lvm /opt

My boot toolset currently consists of grub-2.00-r1, kernel-3.6.4, dracut-024, lvm-2.02.95-r4 and openrc-0.11.2

Kernel Configuration
Before compiling the kernel, make sure to include all the required configurations. For this setup, the most important ones are:

CONFIG_BLK_DEV_INITRD
CONFIG_DEVTMPFS
CONFIG_MODULES
CONFIG_SYSVIPC

Dracut Configuration
Before installing dracut, the desired modules have to be configured in /etc/make.conf. :

DRACUT_MODULES="caps lvm mdraid syslog"

For this setup at least the “lvm” module is mandatory. Further dracut was built with the “device-mapper” USE flag enabled.

Altough some Linux developers (especially from Red Hat/Fedora) advice against a separate /usr partition because of many boot time dependencies on this system path, I didn’t bother much to change my years old setup. Since version 014, dracut includes a module to fill this gap (/usr/lib/dracut/modules.d/98usrmount/mount-usr.sh). It simply mounts the /usr partition right after the root file system early in the boot process. Therefore we have to make sure that the dracut modules “usrmount” and “lvm” are included in the initramfs, which was possible without any manual modification of /etc/dracut.conf, when generating the boot image with:

dracut -H

Kernel Command Line Configuration
Dracut runtime parameters are given on the kernel command line in the Grub configuration. To automatically enable the LVM Volume Group and spawning a debug shell in case the boot should fail, I added the following parameters in grub:

root=/dev/vg_merkur/slash rd.lvm.vg=vg_merkur rd.shell

LVM Configuration
Since dracut is now responsible to enable our volume group, the corresponding init script has to be disabled:

rc-update del lvm boot

Fsck and Fstab
When booting the system now, the /etc/init.d/fsck script will complain that it cannot check the file systems which are already mounted. Fortunately, the init script allows us to define that fsck should be only run when specific “fs_passno” values are set. I therefore this value to “1” for the file systems which are mounted by dracut and to “2” for all the file systems which should be checked by OpenRC. Take care, when specifying a value of “0”, the file system will be never checked for consistency:

# [fs] [mountpoint] [type] [opts] [dump/pass]
/dev/vg_merkur/boot /boot ext2 noatime,nosuid,nodev 0 2
/dev/vg_merkur/slash / ext4 noatime,discard 0 1
/dev/vg_merkur/usr /usr ext4 noatime,discard,nodev 0 1
/dev/vg_merkur/var /var ext4 noatime,discard,nosuid,nodev 0 2
/dev/vg_merkur/opt /opt ext4 noatime,discard,nosuid,nodev 0 2
/dev/vg_merkur/tmp /tmp ext4 noatime,discard,nosuid,nodev 0 2
/dev/vg_merkur/swap none swap sw 0 0

In /etc/conf.d/fsck we then can define, that the fsck init script should only care about file systems with a “fs_passno” larger than “1”:

fsck_passno=">1"

That’s it… If you have some questions or hints, please leave a comment.

Migrate trac-0.11.x from Debian Etch to Lenny

 Admin Hints, Debian, GNU/Linux  No Responses »
Oct 182009
 

Since I was using the nice FineGradePermissions feature of the trac 0.11 release, and Debian was only providing trac-0.10.3 in Etch, I had a custom trac installation running on my Etch server. For migrating to Lenny you would normally think that it’s enough to just copy your project directory to the new installation. Unfortunately this results in a nasty error message:

DatabaseError: file is encrypted or is not a database

Hmn, so let’s check the trac migration guide which advises you to first export the sqlite database with sqlite3 in a plain SQL file. Not much luck here either, the result is an empty database:

# sqlite3 trac.db .dump
BEGIN TRANSACTION;
COMMIT;

The reason is the trac installation in Etch was using the python-sqlite-1.0.1 back-end which uses the SQLite 2 format while in Lenny there is python-pysqlite2-2.4.1 which only knows about SQLite 3.

The conversion from SQLite 2 to 3 can be done by first exporting the database with the sqlite tool and then re-importing it with sqlite3:

# sqlite trac.db .dump | sqlite3 trac3.db

More infos about this can be found at the trac upgrade notes from 0.8.x to 0.9.

Finally your trac installation should work again as usual.

Using vanilla kernel to run as ‘paravirt_ops’ Xen domU

 Admin Hints, GNU/Linux  No Responses »
Oct 162008
 

Xen is nowadays a widespread approach to run virtual hosts. Thanks to its flexible configuration it’s not only possible to run virtual Linux hosts but nearly any operating system that is compatible to the Xen hypervisor machine architecture will possibly run as guest host. The Xen paravirtualization Continue reading »

Gentoo: QEMU in 32bit Xen environment

 Admin Hints, Gentoo, GNU/Linux, Open Source  No Responses »
Oct 032007
 

Recently I wanted to set up a testing server for the different virtualization techniques for Linux. For this I have an Asus P5LD2 mainboard with an Intel dual core Pentium D 3,2 GHz which supports the Virtual Machine Extensions (VMX). Thanks to this I can compile Xen with the ‘hvm’ USE-flag and run fully virtualized guest operating systems on my Xen supervisor. This means I could run nearly every i386 compatible operating system (even Windows 😉 ) in my Xen environment. Without such hardware every guest operating system has to have a Xen enabled kernel.

Another approach with the same result is the open source project QEMU. Its abstraction level is higher than with Xen and it can even emulate different target architectures from your current x86 host. So far x86_64, ARM, SPARC, PowerPC, MIPS and M68k target systems are supported. Its guest operating system does not need any single change to run on QEMU. This makes it very comfortable to test new live CDs or operating system images. But it is not so trivial to setup QEMU and Xen together on a Gentoo machine.

How to setup QEMU on 32bit Gentoo in Xen dom0?

If you compile Xen on a 32bit host you have to add ‘-mno-tls-direct-seg-refs’ to your CFLAGS. That is because the glibc TLS library is implemented in a way that will conflict with how Xen uses segment registers. For compiling the non-patched QEMU 0.9.0 you have to use a gcc version 3.x. The nowadays default gcc 4.x is not yet supported. After several compile failures I finally found to setup QEMU the following way:

1. For compiling gcc-3.x remove the ‘-mno-tls-direct-seg-refs’ from /etc/make.conf and set the ‘nossp’ and ‘nopie’ USE-flags. Otherwise gcc or later qemu will not compile.

2. Switch to gcc-3.x before compiling qemu-softmmu, qemu-user and qemu. In my case it’s: gcc-config i686-pc-linux-gnu-3.3.6

3. Check your CFLAGS again because the optimization flags for gcc 4.x are not always backwards compatible to gcc-3.x. In my case the make.conf looks like this:

# gcc-3.x
CFLAGS="-march=pentium4 -O2 -pipe -fomit-frame-pointer -mno-tls-direct-seg-refs"

# gcc-4.x for compiling gcc-3.3
#CFLAGS="-march=prescott -O2 -pipe -fomit-frame-pointer"

# gcc-4.x
#CFLAGS="-march=prescott -O2 -pipe -fomit-frame-pointer -mno-tls-direct-seg-refs"

4. Now you can compile QEMU. Do not forget to switch back to your original CFLAGS and gcc-4.x after successfully emerging QEMU. I recommend to you to also build the QEMU kernel accelerator module kqemu which has to be compiled with the same compiler as the kernel itself.

Now Xen and QEMU are able to run whatever operating system image you give them. Have fun with playing around…

Additional links:

DokuWiki – A small Wiki for everyday use

 Open Source  No Responses »
Sep 262007
 

For organizing our move to the shared flat I was looking for a small, simple to use Wiki for collecting ideas and coordinating our flat inventory. After a little search I found DokuWiki. It can be easily installed by every Linux distribution’s package manager. Unfortunately the stable Debian package was not the newest version and annoyed me with banners that there are some upgrades available. So I tried again with the newest version from the developers site. After unpacking, the directory has to be made accessible through your Web server and after running the install.php where you actually only create the administrator user, the Wiki is already prepared to use. In the default configuration there is no database needed. But the strength of this Wiki is that it can be expanded by more sophisticated configurations using MySQL or an LDAP back-end for user administration. The syntax is quite simple and similar to other Wiki systems. Also my friends were surprised by the usability of this piece of Open Source software. So if you are planning to use a powerful but simple Wiki software, keep an eye on DokuWiki.

Finally I have my own public IP

 News, Website  No Responses »
Sep 182007
 

This information is for all of you quite boring I know, but it is a happy thing for me. Finally my Xen domain, where I am hosting this Web site, has its own static public IP (193.138.215.129). Now I am ready for running all possible Internet services depending how I feel like. My first plan will be an own mail server with qmail. I am open about some tricks and hints about this. I eventually also found a domain name that suits for this site. When I do not change my mind again, the blog will be soon available under http://www.linuxmonk.ch.

There is a lot changing in my life at the moment so stay tuned for some more news later…

 Posted by at 16:05

Open Source Instant Messaging with GoogleTalk

 Open Source  No Responses »
Aug 162007
 

Most of you may have a similar problem. A lot of friends are present in the Internet but all of them use a different instant messenger. There are ICQ, MSN, Yahoo Messenger, Jabber and a lot more. With multi-protocol messenger like Pidgin (former Gaim) or Adium it is not that laborious to manage all your contacts anymore. But still you would like to reduce your number of accounts as much as possible.

Once more open source software gives an example how it could be. The protocol is called XMPP and originally used by Jabber. When Google introduced their own messenger GoogleTalk in 2005 they made the wise decision to also use XMPP instead of inventing a new protocol. The next big thing is that everybody with a Gmail account can also use this credentials for GoogleTalk. One account connects you to your friends of two networks. Why is not everything in information technology so handy?

Now you are maybe wondering that Gaim/Pidgin does not support GoogleTalk. But it does support Jabber/XMPP. So it is an easy thing to set up your GoogleTalk account. Enter your Gmail address as “Screen Name”; the server is not “jabber.org” but “gmail.com” and the connect server is “talk.google.com”. As resource you can leave “Home”. Finished and ready for chatting…

Arming against SSH Attacks

 Admin Hints, GNU/Linux, Open Source  No Responses »
Jul 242007
 

I think everybody that runs an own Linux server with the SSH daemon listening on port 22 is sooner or later annoyed by the amount of password attacks done by bots somewhere out in the Internet. What can you do against it?

Blocking via iptables ‘recent’ module
How you can do this on a Gentoo system is described in the Gentoo Wiki here. Because it blocks the connection attempt only due to the number of tries within a certain time it is a very basic solution and needs quite a lot of testing to examine the good parameters for the ‘hitcount’ and ‘seconds’ arguments. You do not unintentionally want to block yourself when you only try to open several connections within a short time period. So not really the thing I recommend here.

Log parsing with sshguard
sshguard uses another approach. It parses the SSH log messages and searches for login failures. For example when you try to connect with a non-existent user sshguard catches it and creates an iptables deny rule. But also sshguard has a small design mistake. It wants you to create a sshguard chain in iptables and redirect all the traffic to the chain assuming that your default INPUT policy is ACCEPT. When it wants to block a host it runs iptables -A sshguard -s host-to-block -j DROP. In case you have your policy set to DROP you cannot configure the iptables to accept the allowed SSH traffic because else the blocking rules will not work anymore. I made a small patch to change the blocking command to insert the rule in first place of the chain. After you applied the patch you have to make sure that you setup your iptables the following way:

iptables -N sshguard
iptables -A sshguard -j ACCEPT
iptables -A INPUT -p tcp --dport ssh -j sshguard

Further you have to edit your system logger configuration file. Please read the documentation.

For all the lazy people I even made a Ebuild that also adds a second patch where you can disable the IPv6 ability of sshguard. You can find it here.

Migration of Xen SMP domU

 Admin Hints, GNU/Linux, Open Source  No Responses »
Jul 092007
 

YES, YES, YES! Finally I made it.

Since a while I am playing with the migration functionality of a Xen domU between two Xen servers. It allows to move a virtual machine without reboot between two physical machines. But my problem was: It did not hold what it promised.

Trying all possible versions of Xen and the xen-sources in the Gentoo Portage I was able to migrate a domU but not when it was configured as SMP machine. After I found that the kernel has to include the CONFIG_HOTPLUG_CPU option, I was able to migrate the domU at least one time from one host to the other. When repeating this procedure the domU crashed with a kernel oops. By finally trying the latest Xen 3.1 version from the unofficial mescalito portage overlay with the xen-sources-2.6.18, repeated migration of a domU between the Xen servers does work now. Prerequisite is that both dom0 and domU run the 2.6.18 kernel. I am trying to run this in production now and will see how reliable it is.

I just remember that I did also remove the memory restriction from the dom0. The dom0_mem parameter in the grub configuration is optional and when omitting it the dom0 can use the unused memory for itself.

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