Craig Mayhew’s Blog

Shortly after logging into Gnome I was getting the following error:

“The application “gnome-panel” attempted to change an aspect of your configuration that your system administrator or operating system vendor does not allow you to change. Some of the settings you have selected may not take effect, or may not be restored next time you use the application.”

Clicking the “details” button brings up the following message: “No database available to save your configuration: unable to store a value at key ‘/apps/panel/toplevels/top_panel_screen0/expand’, as the configuration server has no writable databases.”

I had messed up my permissions in the .gconf directory that stores many of Gnome’s settings. In my case the execute permission was missing from the folder and all files within it so Gnome gave that error.

To fix this run the following commnd on your gconf directory. It will give your user read, write and execute permissions to the gconf folder and all files/folders within it which should solve the problem.

sudo chmod -R  u+rwx ~/.gconf

When I have too many applications open or one of them eats all the memory I end up with a big chunk of my swap space used. The problem is that once I’ve closed a few programs or killed the offending program my computer still uses the swap space! I’ve read that the swap space will slowly be loaded back into RAM but only when it is next accessed. This results in sluggish system performance when the applications next read the memory in the swap space. To solve this problem you can empty the swap space and load it all back into RAM with one simple command. Please make sure you have enough RAM installed to load the memory in swap back into RAM…

This switches off swap memory and forces the system to load it back into RAM:

sudo swapoff -a

This switches swap back on incase you run out of RAM in the future:

sudo swapon -a

So now I can run those two commands, have the computer busy for 10-15 seconds and then know that it won’t slow down again due to needing to access the swap (Unless it runs out of RAM again).

Download VMWare Server from http://www.vmware.com/products/server/

Extract the tar file to somewhere convenient, in this case I’m going to extract it to the desktop.

Execute vmware-install.pl which is in the vmware-server-distrib folder that you just extracted. You will be prompted by questions about install directories. I managed to get away with pushing enter for the default value on all of these questions. It may need to recompile some files if it isn’t familiar with your kernel version. This isn’t normally a problem if you have a c/c++ compiler.

If you don’t have a c++ compile (here’s how to check and install one) then get one from synaptic packaged manager.

When asked, make sure you respond “yes” and give your ubuntu username when prompted to change the username (if this bit goes wrong then once VMWare Server is installed you will need to uninstall it and start over). After answering more prompts the installer will ask for your serial number. This can be obtained from the VMWare website for free.

Caveats:

1) If you accidentaly left the username blank then you will need to run the following command to uninstall the vmware server. You will then need to start the install again.

sudo /usr/bin/vmware-uninstall.pl

2) To access the server admin you need to visit either https://127.0.0.1:8333/ui/ or http://127.0.0.1:8222/ui/ in a browser. You can then login with your ubuntu account username and password.

Click the System Menu and then click “Synaptic Package Manger”:

Then type gcc into the quick search box. The list may make take a moment to update. Then if you don;t have a blue box next to gcc like I have in the example then click the empty box and click “Apply” to install the gcc package.

The new network manager is a massive improvement over the previous network tools in Ubuntu. Coming from a windows background I am used to routing tables being updated automatically. However, after connecting to a VPN using the Ubuntu 9.04 network manager I’m unable to access or even ping anything on the remote network, yet the VPN is connected. This is due to the computer not knowing about the computers on the VPN. This is where routing tables come into play. My works ip range is 192.168.10.* so this needs to be added to the routing table.

The easiest way to do this is to have the network manager handle it all by adding a setting in the network manager like so:

Click on the network manager icon then “VPN Connections” and the following menu should appear: Click “Configure VPN”.

Click the VPN tab. The VPN you have already created should appear in the list. Click your VPN and then click edit.

Another window should appear, click the “IPv4 Settings” tab. Then click the “Routes…” button.

Now you need to add a route so your computer can talk to other computers on the VPN. In this case I have added the address as 192.168.10.0 as all computers on the office network have an IP that begins with “192.168.10″ and a netmask of 255.255.255.0. The gateway is the IP of my home router, in this case my home router is “10.11.12.1″.

At this point it’s also worth mentioning as a side note that if “Use this connection only for resources on its network” is NOT ticked then all of your regular internet traffic will go via the VPN and not just when you want to access something on VPN like shared files and folders. This would really slow down your internet access. I personally would have this ticked.

And there you have it, that will now allow your computer to talk to other computers on the office/remote network.

For those of you who want a more hands on approach and really want to see whats going on behind the scenes (everyone else stop reading here):

Run the route command to view the routing table:

route

This is the route table with the missing route:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
office.mywork   my.router       255.255.255.255 UGH   0      0        0 eth2
10.11.0.0       *               255.255.0.0     U     1      0        0 eth2
link-local      *               255.255.0.0     U     1000   0        0 eth2
default         my.router       0.0.0.0         UG    0      0        0 eth2

The network manager automatically adds the correct route to the routing table when the VPN connection is created. You can achieve the same result with the following command. In this case we are using the network range 192.168.10.*:

sudo route add -net 192.168.10.0/24 ppp0

Now check the routes table again:

route

And here we have a route that allows us to access computers on the remote network:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
office.mywork   10.11.12.1      255.255.255.255 UGH   0      0        0 eth2
192.168.10.0    *               255.255.255.0   U     0      0        0 ppp0
10.11.0.0       *               255.255.0.0     U     1      0        0 eth2
link-local      *               255.255.0.0     U     1000   0        0 eth2
default         10.11.12.1      0.0.0.0         UG    0      0        0 eth2

After upgrading to Ubuntu 9.04 I’ve found the network manager GUI to be far superior to the previous version I was using in Ubuntu 8.04 LTS. Unfortunately when I was using Ubuntu 8.04 I made some custom alterations to my network setup in the “/etc/network/interfaces” file. The Network Manager in 9.04 wasn’t keen on this and so refused to manage it, instead it displayed the message “Wired Network – device not managed”.

As a work around I commented out all of my changes by placing a # at the beginning of each line in my interfaces file:

Open the interfaces file in an editor:

sudo vim /etc/network/interfaces

This is an example of how my file looked before I modified it. Yours will be different:

auto lo
iface lo inet loopback
iface eth2 inet static
address 192.168.0.44
netmask 255.255.255.0
gateway 192.168.0.1
auto eth2

And here’s the same file again, but I’ve added #’s at the beginning of each line so that they are ignored:

#auto lo
#iface lo inet loopback
#iface eth2 inet static
#address 192.168.0.44
#netmask 255.255.255.0
#gateway 192.168.0.1
#auto eth2

In order for the changes to take effect, we need to restart the network manager and the applet by running each of these in the command line:

sudo /etc/init.d/networking restart

And now restart the network manager applet:

pkill nm-applet
nm-applet

You should now be able to manage the network connection from within the network manager applet.

After upgrading to Ubuntu 9.04, Gnome-RDP stopped working. When I opened it I was greeted with the following errors:

The settings database file has become corrupted or at least it can no longer open it. If your happy to cut your losses and start with a fresh settings file then run this command to rename your Gnome-RDP database file:

mv ~/.gnome-rdp.db ~/.gnome-rdp.db.damaged

This will mean you lose your Gnome-RDP settings and you will need to re-enter them, however you will be able to use Gnome-RDP again! The file will be renamed to .gnome-rdp.db.damaged so you can retrieve that file in the future.

If you have Ubuntu 8.04 LTS installed but have decided that the speed improvements and nicer interface for 9.04 are just too good to wait for the next LTS, you will need to do the following:

“System” -> “Adminstration” -> “Software Sources”

Click the Updates Tab. Set “Release Upgrade” drop down to “Normal releases”, click “Close”. This will allow you to upgrade to versions of Ubuntu which do not come with long term support (LTS).

Run the Update Manager. Click “Distribution Upgrade”. This will begin the upgrade to Ubuntu 8.10.

During the upgrade process it may ask you to replace a few files that it detects you have customised. For me it asked to overwrite my cutomised printer setup and also undo modification I had made to the way ubuntu uses virtual memory. Don’t forget to make a note of these as you will need to add this customisations again manually later if you still require them. When prompted, restart.

After rebooting, my copy of ubuntu crashed during the boot process due to a problem with the latest kernel it had installed. It crashed on boot due to issues with not being able to mount the root file system. This was easily solved by pressing escape to view the grub menu during the boot process. I then selected the older kernel version from the list of available kernels. It then booted happily into Ubuntu 8.10!

At this stage I took the time to notice the better network interface GUI, better support for wireless and VPN connections. It wasn’t too long before a message popped up telling me that Nvidia had some new drivers for my graphics card! This is excellent news for me because previously I had a script to recompile my graphics drivers each time a new kernel was installed due to the graphics card being so new. However we don’t want to stop here, we’re going for Ubuntu 9.04!

Once again run the “Update Manager” found under “System”->”Administration”. Click “Upgrade”. It will prompt you with a few messages. Click Start and Upgrade where necersary.

If the process appears to get stuck downloading a particular package when it’s at the stage “Getting New Packages” then click cancel. Go back to the update manager and start the upgrade process again. It will start from where it left off and won’t redownload the packages it has already downloaded.

Once it has finished upgrading, remove obsolete packages and restart when prompted.

There you have it! You should now be running ubuntu 9.04!