Feb 6, 2013

Moved blog to my own domain

I have transfered this blog to blog.ochotnicky.com If you have been using my feedburner feeds, they should keep working. If however you are using blogger feeds directly, you will have to update them to http://blog.ochotnicky.com/feed. Alternatively you can use feeds for specific category depending on your interests. For example http://blog.ochotnicky.com/category/fedora/feed contains only posts related to Fedora.
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Sep 13, 2012

Gentoo Boot Optimization

Justification

There is something Zen about boot time optimization. Let's face it, most of us don't reboot our Linux machines all that often. Yet shaving off a second or two from boot process gives me certain type of satisfaction.

Recent post on Google+ by Lukáš Zapletal made me try out bootchart for the first time. Original post was about e4rat - a tool for defragmenting ext4 partitions to optimize them for boot speed when using traditional rotational media. I decided to have a look at my bootcharts and see what can be done on my SSD based Gentoo system.

Bootchart Installation

I am not going to go into details. Just install from your distribution repositories. Gentoo contains app-benchmarks/bootchart2 in base portage tree, and Gentoo wiki has all the instructions you'll need.

First run

After I installed bootchart, my initial result was 11 seconds from init to X server running and showing password prompt. Let's analyze the Bootchart (200kB png) a little bit. It looks like slim was waiting for runscript.sh to finish. Not visible in the image, but that is actually net.eth0 script. In other words: network configuration, dhcp. Since I have stable IP address in my local network, I decided to stop using DHCP. For a simple Gentoo system this can be achieved by editing /etc/conf.d/net (configuring IPv4 and IPv6 statically):
    $ cat /etc/conf.d/net
    config_eth0="A.B.C.D/24 2001:470:413b:0:2e2:d4ff:ff8d:ccd1/64"
    routes_eth0="default via A.B.C.1"
  
So how are we faring after making our IP static? 5 seconds! At this point I'd be willing to say mission accomplished, but something told me there's more to do...

Let the fun begin

Looking at the second bootchart tells us one thing: xdm/slim is waiting for my ntfs partition to get mounted. We should probably avoid that!

What I decided to try was installing autofs and just mounting my /shared-data partition when it's actually accessed. To my dismay, the resulting bootchart showed that the boot got even slower! (5.6 seconds). Time for the big guns baby!

Mini-optimizations

The problem with XDM seems to be that it is waiting for something. Let's have a look at /etc/init.d/xdm snippet:
depend() {
        need localmount xdm-setup

        # this should start as early as possible
        # we can't do 'before *' as that breaks it
        # (#139824) Start after ypbind and autofs for network authentication
        # (#145219 #180163) Could use lirc mouse as input device
        # (#70689 comment #92) Start after consolefont to avoid display corruption
        # (#291269) Start after quota, since some dm need readable home
        # (#390609) gdm-3 will fail when dbus is not running
        # (#366753) starting keymaps after X causes problems
        after bootmisc consolefont modules netmount
        after readahead-list ypbind autofs openvpn gpm lircmd
        after quota keymaps
        before alsasound

        # Start before X
        use consolekit dbus xfs
}
XDM seems to have a lot of dependencies. It is understandable because distributions will always prefer correctness over speed (hopefully). We are running a simple desktop. No network authentication, no heavyweight display manager or desktop environment like KDE or GNOME. So what happends if we remove netmount and autofs from requirements of xdm? After all we don't need them to start slim. Final bootchart is much more interesting. Roughly 3.5-4 seconds from init to X!

Quo Vadis

I finished with that 3.5-4 second boot. But as the final bootchart shows there's still room for improvement. List of things that could probably be looked into:
  • blkid takes too long. Perhaps we could avoid it completely?
  • e1000 (network card) and i915 (graphics card) take quite a while to initialize. Perhaps having e1000e as module and loading it later during boot would be faster
  • Not using LVM would speed things up, but I like its advantages
  • Avoiding udev could be useful as well for static system where no USB devices are to be attached dynamically
  • While we are at it, disabling USB completely would save around 250ms as well

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Feb 21, 2012
Recently I wanted to make use of my 16GB usb drive in a sensible way, and I didn't really need another classic pendrive for moving data. In the end I decided to install BackTrack on it. BackTrack is a general forensic analysis/penetration testing distribution based on Debian. And it's fairly nice as far as a rescue distribution too.
I could have installed with with UNetbootin, which has direct support for BackTrack, but I wanted something a little more fancy: full disc encryption and persistence of data.
There is a very nice how-to linked from main BackTrack website for doing exactly this sort of thing. But I didn't want to burn the image first or even reboot. We have virtualization for that today! Right? Right! Or not...
So I downloaded BackTrack KDE/64bit variant iso, checked the md5sum to be correct, and started installation. Silly me thoght that running a KVM VM like this would make it possible to install BackTrack on the usb drive:
$ virt-install -n test -r 1024 --cdrom BT5R1-KDE-64.iso \
             --boot cdrom --nonetworks --graphics spice \
             --disk path=/dev/sdg
    
Where BT5R1-KDE-64.iso would be my BackTrack iso image and /dev/sdg would be my USB drive. Sadly this failed with ugly error message after BackTrack started booting:
# (initramfs) mount: mounting dev/loop0 on //filesystem.squashfs failed
    
After some investigation I found out that BackTrack booted fine if it was the only drive in the system, but failed with the above messages when I tried to attach my USB drive. Never found the reson, but the solution was to make the USB drive use virtio bus like this:
$ virt-install -n test -r 1024 --cdrom BT5R1-KDE-64.iso \
             --boot cdrom --nonetworks --graphics spice \
             --disk path=/dev/sdg,bus=virtio
    
After that I just continued according to the how-to with a few differences (such as USB key being seen as /dev/vda). Welcome our encypted overlords.

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