Arrfab's blog Some tips and tricks, mostly around CentOS

We use DRBD at work on several CentOS 5.x nodes to replicate data between our two computer rooms (in different buildings but linked with Gigabit fiber). It's true that you can know if something wrong happens at the DRBD level if you have configured the correct 'handlers' and the appropriate notifications scripts (Have a look for example at the Split Brain notification script). Those scripts are 'cool' but what if you could 'plumb' the DRBD status in your actual monitoring solution ? We useZabbixat \$work and I was asked to centralize events from differents sources and Zabbix doesn't support directly monitoring DRBD devices. But one of the cool thing with Zabbix is that it's like a Lego system : you can extend what it does if you know what to query and how to do it. If you want to monitor DRBD devices, the best that Zabbix can do (on the agent side, when using the zabbix agent running as a simple zabbix user with /sbin/nologin as shell) is to query and parse/proc/drbd . So here we go : we need to modify the Zabbix agent to use Flexible User Parameters, like this (in /etc/zabbix/zabbix_agentd.conf …

The number of questions I received from different people regarding the LiveCD/LiveDVD tools and the kickstart files used to produce the ISO images was quite "high". People looking at the normal place will be disappointed because we haven't used the original livecd subversion repo to produce the actual Live medias.  So in the meantime, if people want to use the livecd-creator tool, they can fetch the SRPM here : http://people.centos.org/arrfab/CentOS6/SRPMS/livecd-tools-0.3.6-1.el6.src.rpm . I've just copied also the two kickstart files used for both LiveCD and LiveDVD here :http://people.centos.org/arrfab/CentOS6/LiveCD-DVD/

Hope that people will be satisfied .. faster to push those files there than to change the whole 'used behind the scene' infra

As you've probably seen if you're subscribed to the CentOS announce list (or if you just rsync/mirror the whole CentOS tree) , the CentOS 6.0 LiveCD was released last monday. This is the first of our CentOS custom spins ! While I'm writing that blog post, the CentOS 6.0 LiveDVD is on its way to the external mirrors too and will normally be announced shortly (when enough mirrors will have it) ! It will be the second CentOS respin and we have more in the pipe for you ! As Karanbir announced it in the 6.0 release mail , we planned also to provide two other spins : the minimal one and the lws one. Good news is that the minimal one is almost finished and being intensively tested. If things don't change (or bugs appear during QA), the iso image will be only \~250Mb for the i386 arch and \~300Mb for the x86_64 one. It's meant to be used as a real basic CentOS system (even less packages that the @core group on a normal install if used with the proper kickstart invocation !) : 186 packages only on your disk. You'll have a very basic CentOS system with only openssh-server and yum …

I decided to put CentOS 6 on my iMac. It was running in dual-boot mode with OSX and CentOS 5. Installing through the network (from a NFS share) was really easy and no bug encountered but at the end of the install, when it asked me to reboot, nothing : after having selected the Linux partition in the rEfit boot manager screen, nothing. hmm ....

I restarted the install process to see if at least anaconda tried to install grub on the first sector of the /boot partition and not in the MBR but that was correctly seen and chosen by anaconda . So the issue was somewhere else. I had a /boot ext3 partition (on /dev/sda3) while /dev/sda4 is the VolumeGroup in which I had defined my Logical Volumes. There was a big rewrite in Anaconda for the storage part and el6/CentOS 6 suffers from one bug found on the upstream bugzilla when having to deal with Apple computers *and* using rEfit at the same time : https://bugzilla.redhat.com/show_bug.cgi?id=505817

Long story short : to have CentOS 6 running on your iMac (if using refit as the EFI boot manager) :

• install CentOS 6 as usual (check …

One thing that I had to have a look at (during CentOS 6 QA), is the way anaconda (the Red Hat/Fedora/CentOS installer) pre-defines some 'tasks' . People used to those kind of install know what I'm talking about : the "Mininal", "Desktop", "Basic Server" and other choices you have during setup. From that first selection, you can decide (or not) to customize the software selection which then leads you to a screen containing categories / groups / packages defined in the comps.xml file present under /repodata on the tree/install media.

If you don't 'see' which screen i'm talking about, a small screenshot of the upcoming CentOS 6 will explain better than words :

Those pre-defined tasks aren't defined in the comps.xml file but rather at build time within anaconda. Fine but how can you 'modify' anaconda behaviour and test it without having to patch anaconda SRPM, rebuild it and launch a new build to generate the tree and install medias ? Easy , thanks to a simple file on the tree !

People wanting to modify anaconda behaviour at install time without having to regenerate the whole tree can just create a small file (updates.img) , put it in the /images directory in …

It seems quite a lot of people blogged aboutIPV6 day . It's true that it's always a good idea to speak about IPV6. I'm using IPV6 natively on my server hosted atHetzner (they offer a /64 IPV6 subnet, which is more than enough for a CentOS server hosting several xen domU Virtual Machines). At home, that's another story. I use aHE.net free tunnel to be able to reach ipv6 hosts. Yes, even in 2011, you still have to use tunnels to use IPV6 ! Why ? that's indeed a good question. Even if my CentOS ipv6 tunnel end-point/router/radvd at home is working correctly, I decided to ask my belgian provider if they had plans on implementing native IPV6. Well, not for my home connection, as I already know that Belgacom (the biggest provider in belgium) doesn't support IPV6 on their BBOX2 modems that they give to customers when ordering a DSL connection at home (while i'm talking about Belgacom, please stop sending me direct advertisement to my mailbox - the real one and not the electronic one - with your invoices about a service - VDSL2/BelgacomTV - that you *can't* offer to all your customers ... thanks) . So I decided to …

I couldn't believe what I read yesterday .. but yes, Nokia has decided to sign a special partnership with Microsoft to load WM7 on their mobiles phones in the future .. The end of Symbian and Meego/Maemo .. sad, sad .. time for me to think about my next mobile phone. Official Nokia announce here :http://conversations.nokia.com/nokia-strategy-2011/

As you probably know (if you are interested in the Enterprise Linux market), Red Hat released earlier today 5.6 . So automatically some CentOS QA team members started to discuss about that in the appropriate IRC channel. As CentOS 6.0 isn't (yet) released nor ready, the discussion was about putting 5.6 build & release as priority number one or not. Karanbir on his side asked on Twitter about thoughts on the matter, and a discussion was started too on the centos-devel list about that topic. My personal opinion (and shared by some people too) seems to give 5.6 the priority for quite some reasons :

• The centos 5.x install base is there while there is (obviously) no centos 6 install base.
• So those people having machines in production, faced to the net (, etc, etc, ...)  would prefer having their machines patched and up2date (security first !)
• People running CentOS 5.x on servers and willing to install php53 packages, now officially included
• On the build side, the el5 build process is clearly identified and known since 2007 : packages with branding issues are already identified and patches/artwork is already there, meaning that it will be probably (no, surely !) faster to …

Some members of the CentOS team will be present at the Fosdem . Feel free to come at our booth just to discuss ...

More informations on our wiki and on the Fosdem website

I was playing with IPv6 in the last days (started to use a tunnel from he.net as my current ISP doesn't support  native IPv6 and doesn't plan to support it in a short time) and wanted to add IPv6 to some of my CentOS Xen domU's running on a Hetzner box. This part was a little bit more difficult than for a standard network. Due to their internal network design, Hetzner only allow 'routed' xen networks and not standard 'bridged' ones. What I used for IPv4 was just binding the public IPs on the dom0 and configured all my iptables rules there to forward/SNAT/DNAT to the appropriate domU. But you know that NAT is gone with IPv6 so normally it's supposed to be easier, right ? Well, yes and no, depending on your network layout. Even after  having enabled ipv6 forwarding (net.ipv6.conf.all.forwarding=1 ), I was just able to ping the dom0 but not the guests behind. Hmm, that reminds me the proxy ARP that was used for IPv4 but not existing anymore for IPv6 (gone too ...) . ARP was (more or less, not technically correct but read the RFCs if you enough time) replaced by …