digging hard links

A couple of tips about hardlinks: to find all hard links in a specific namespace use something like this:

$ find -type f -links +1

this because hard links have, by definition, more than one link pointing to them, as you can see with ls or stat on one of them.

Another useful tip: to know about any hard link which is related to a specified file use something like:

$ find /home -xdev -samefile foo

this will print out all files which are hardlinked to foo. Remember that hard links have the same inode number which can be seen with

$ ls -li foo

once you know the inode number, you can also search for hard links with something like

$ find /home -xdev -inum 7465209

Have fun!

How to run ChromeOS under VMware

Starting from this announcement

http://www.unixmen.com/news-today/706-chromium-os-zero-released-

I wanted the try out ChromeOS but under VMware and have a look at it. The first thing is to convert the downloaded raw image to VMWare disk image format:

$ qemu-img convert -f raw ChromeOS-Zero.img -O vmdk ChromeOS-Zero.vmdk

Then start VMware player and create a new virtual machine, but select "Custom". At some point during the process, it will ask you to select a disk. Choose to use an existing virtual disk, and point the installer tothe file created above.

This is the only trick you need to complete the virtual machine creation. Now to see what is all this ChromeOS fuss about ...

Yum and RPM notes for multiarch machines

When installing something on a stock 64bit installation, yum will by default install both x86_64 and i386 (if available) packages. This default behavior is often appearing when installing libraries and can be changed
by adding the following to /etc/yum.conf

multilib_policy=best

(default to all). In this way only the matching arch package will be installed.

If you don't want to make this global change, you can issue the yum command as follows to have the same outcome but for one time only:

yum install libtool-ltdl.x86_64

i.e. append the arch to the package name to avoid i386 package to be pulled along.

Querying the rpm database on x86_64 machines often shows duplicate packages, but that's normal in light of the above. You can change the default query format on the fly, e.g

rpm --qf '%{NAME}.%{ARCH}\n' -q glibc

or you can make it global by adding this to /etc/rpm/macros

%_query_all_fmt         %%{name}-%%{version}-%%{release}.%%{arch}

In this way the arch will be shown alongside other query parameters.

Accessing the guest OS from the host using VirtualBox

To be able to access the guest OS via ssh fro the host, type the following on the host

$ VBoxManage setextradata Centos\ 5.3\ x86\ bis "VBoxInternal/Devices/pcnet/0/LUN#0/Config/SSH/HostPort" 3333
 $ VBoxManage setextradata Centos\ 5.3\ x86\ bis "VBoxInternal/Devices/pcnet/0/LUN#0/Config/SSH/GuestPort" 22
$ VBoxManage setextradata Centos\ 5.3\ x86\ bis "VBoxInternal/Devices/pcnet/0/LUN#0/Config/SSH/Protocol" TCP

(SSH is just a string, you can type anything really). Then you can login to the guest OS by typing this on the host:

$ ssh -p 2222 -X root@localhost

note the same principle applies to other services, example for httpd:

$ VBoxManage setextradata GuestName "VBoxInternal/Devices/pcnet/0/LUN#0/Config/Apache/HostPort" 8888
$ VBoxManage setextradata GuestName "VBoxInternal/Devices/pcnet/0/LUN#0/Config/Apache/GuestPort" 80
$ VBoxManage setextradata GuestName "VBoxInternal/Devices/pcnet/0/LUN#0/Config/Apache/Protocol" TCP

then you can point the host browser to http://localhost:8888. Note that you can’t use a host port lower than 1024 without running VirtualBox with escalated privileges.

To see settings use:

$ VBoxManage getextradata guestname enumerate

To clear a setting (by giving it a clear value) use:

$ VBoxManage setextradata "VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/GuestPort"

Virtual lab with VirtualBox

To get two virtual guests to talk to each other while also being able to reach out to rpm repos etc. (i.e.  to inernet), one needs to define two interfaces on the VirtualBox guest OS settings:

• first interface (will be eth0) should use default NAT setting. This will provide Internet access.
• second interface (will be eth1) should use 'Internal Network'. This will provide in-between guests connectivity.

When booting the guest (Centos in my case), eth0 will come up via DHCP, then configure eth1 with a static non routable IP address. However when bringing it up, it will override DNS and default GW as set by eth0, therefore breaking internet access. The fastest path recover is to simply restart eth0 (ifdown eth0/ifup eth0) which gets again the correct settings from the dhcp server.

Using IPod Nano on EeeUbuntu

The Nano is formatted with hfsplus (used under MacOSX earlier) hence when plugged under Ubuntu Linux is mounted read-only. To have it mounted read-write you need to plug it on Mac and then issue this command

$ diskutil disableJournal /Volumes/Somebody’s\ iPod/

this will remove the journal from the HFS+ filesystem, and now Linux will mount it read-write. Then use whichever application to manage your songs.

Speeding up firefox 3

In the about:config enable the setting network.dns.disableIPv6 (double click will suffice).
Then install the Flashblock Firefox extension to load the Flash stuff only when you want.
Additionally try to use the fastest SDD drive for the FF cache, instructions below:

• Open a new tab and type about:config into the address bar.
  
• Right-click anywhere in the lower part of the screen and choose new->integer.
• Name the new setting ‘toolkit.storage.synchronous’
• In the second popup, set the value to 0 (zero). This tells the browser not to wait while writing files.
• Create a new string called ‘browser.cache.disk.parent_directory’
• Set its value to ‘/dev/shm/firefox-yourusername’. This tells the browser to use a RAM disk instead of the SSD.

The above procedure placaes the cache in the RAM, however this means it will be lost when shutting down the computer.