• Linux,  Work

    MegaCLI: useful commands

    Recently I installed a server with a Supermicro SMC2108 RAID adapter, which is actually a LSI MegaRAID SAS 9260. LSI created a command line utility called MegaCLI for Linux to manage this adapter. You can download it from their support pages. The downloaded archive contains an RPM file. I installed mc and rpm on Debian with apt-get, and then extracted the MegaCli64 binary (for x86_64) to /usr/local/sbin, and the libsysfs.so.2.0.2 from the Lib_utils RPM to /opt/lsi/3rdpartylibs/x86_64/ (that’s the location where MegaCli64 looks for this library). Here are some useful commands: View information about the RAID adapter For checking the firmware version, battery back-up unit presence, installed cache memory and the…

  • Linux,  Work

    Fixing grub-probe error: Couldn’t find PV, check your device.map.

    Today I was getting this error when installing a new kernel on a server running Debian: /usr/sbin/grub-probe: error: Couldn't find PV pv2. Check your device.map. The error can be reproduce by running the update-grub command. The day before, a new RAID disk was added to this server, so I suspected this could be the cause. The file /boot/grub/device.map contained a reference to the first RAID disk as (hd0) but did not contain a reference to the new RAID disk. I ran # ls -l /dev/disk/by-id/ to find out which SCSI ID referred to sdb (the new RAID disk), and then added the following line to device.map: (hd1) /dev/disk/by-id/scsi-3600304800087c4f015fb4f2e4cc7a8e5 Now installing…

  • Linux

    Tax-on-web with Debian and Firefox

    In Belgium, we can fill out our tax form online on the Tax-on-web site using a smartcard reader and our electronic identity card. Unfortunately, things are rather complicated to set up, partly because the eID authentication is based on SSL renegotiation, a feature which is disabled by default in recent Firefox versions because it can be insecure. It is a bit disappointing that we have to rely on potentially vulnerable technologies to authenticate with our eID, but there is not much choice if you do not want to fill out the paper forms (or are too late, so that the electronic way is the only option). First we need to…

  • Linux,  Work

    Linux performance improvements

    Two years ago I wrote an article presenting some Linux performance improvements. These performance improvements are still valid, but it is time to talk about some new improvements available. As I am using Debian now, I will focus on that distribution, but you should be able to easily implement these things on other distributions too. Some of these improvements are best suited for desktop systems, other for server systems and some are useful for both.

  • Linux

    GNOME Shell moving forward

    Some news about GNOME 3 and GNOME Shell: The minimize and maximize window decoration buttons are now removed. It is estimated that these buttons are not useful actually, and users should be using Alt-Tab, the dock or different workspaces to switch between different applications, and maximize windows by double clicking on the title bar. As this will also make the desktop more difficult to access, I guess this also means that there are no plans to re-implement desktop icons. The problem with the ellipsis of long application names has been fixed by enlarging the icons in the application browser. On the #gnome-shell IRC channel there was a discussion earlier today…

  • Linux,  Work

    Improving Mediawiki performance

    Now that I am on the subject of improving performance, I configured some performance improvements for a Mediawiki installation here: Make sure you run the latest Mediawiki version. Mediawiki 1.16 introduced a new localisation caching system which is supposed to improve performance, so you definitely want this to get the best performance. Create a directory where Mediawiki can store the localisation cache (make sure it is writable by your web server). By preference store it on a tmpfs (at least if you are sure it will be big enough to store the cache), and configure it in LocalSettings.php: $wgCacheDirectory = "/tmp/mediawiki"; Iif /tmp is on a tmpfs, you might add…

  • Linux,  Work

    Improving performance by using tmpfs

    Today I analyzed disk reads and writes on a server with iotop and strace and found some interesting possible optimizations. With iotop you can check which processes are reading and writing from the disks. I always press the o, p and a keys in iotop so that it only shows me processes doing I/O and so that it will show accumulated I/O instead of the bandwidth. With the left and right arrows I select on which columns to sort the list. Once you have identified the processes wich are doing much I/O, you can check what they are reading or writing with strace, for example # strace  -f -p $PID …

  • Linux

    Is Unity a better alternative to the GNOME Shell?

    After my disappointment with the current GNOME 3.0 development version with GNOME Shell, I thought it would be interesting to compare it with Ubuntu’s Unity. Ubuntu has just published a new alpha version of what will become Ubuntu 11.04, so I used that for a quick test. On the positive side: On the dock on the left side there is a button which opens the workspace switcher which gives a nice overview of your virtual desktops and their contents. The workspace switcher is easy to find and it looks awesome: this might be exactly what is needed to make more end users finally get to use virtual desktops. The list…

  • Linux

    GNOME 3.0: Making the same mistakes as KDE 4.0?

    Yesterday Fedora held a GNOME 3 test day. In order to facilitate testing, they published a Rawhide live CD containing the latest builds of GNOME 3. This is a great opportunity to test the latest GNOME-shell and other new things without having to upgrade your system to unstable alpha stuff. I tried it out on my laptop with Intel graphics chipset. After a quick test, I am quite disappointed. Just like KDE 4, GNOME 3 tries to explore some new innovative desktop stuff, but just like KDE 4 in its first versions, it feels extremely unpolished and very unfinished, resulting in a rather cumbersome experience. On the positive side: The…

  • Linux,  Work

    DHCPd failover

    Last week, I set up two dhcpd servers in a fail-over configuration. The goal is that when one DHCP server goes down, the other one takes over so that clients don’t lose their network connection. I read different tutorials on the web, such as this one of a fellow blogger and this documentation published by IBM.