Why would I want to do this? For various reasons such as allow you to access information and servers that are behind a firewall, or maybe you just need to route traffic through different servers.

I’ve tested this on a 256mb Rackspace Cloud instance running Ubuntu 10.04 and with an iPhone and an iPad. Thanks to Yaniv for debugging the instructions.

Disclaimer: This is for educational uses only and I take no responsibility as to what you may do with it. The PPTP VPN setup via the instructions below has no encryption and uses the simplest and lowest form of password authentication. If you require stricter encryption and authentication methods you’ll need to read more about pptpd configuration.

Assumptions:

• The instance you are using is blank, specifically from firewall rules in iptables, otherwise, you’ll need to patch things up.
• All commands assume you are current a root user. If you logged in as root, that’s great. If not, run:
  sudo su
• Instead of messing a lot with iptables commands, I’m using ufw (Uncomplicated FireWall). In general, to most people, it will be easier to manage and work with.

Setting up the PPTP Server

In general we are going to create a PPTP VPN that is very basic without encryption and with basic authentication security (not fancy authentication protocols). Since Rackspace Cloud instance has an external interface (eth0) that has the instance public IP and an internal interface (eth1) with an internal IP used to communicate with your other Rackspace Cloud server (if you have them), we’ll create an alias network interface card that will have some other set of internal ips, which will be given to the devices connected via the VPN.

1. Install the necessary software (pptpd, pptp-linux, ppp and ufw – for firewall):
   apt-get install pptpd pptp-linux ppp ufw
2. Enable port 22 (ssh) in the firewall, so we don’t get locked out of our instance:
   ufw allow 22
3. Enable port 1723 (pptpd) in the firewall to enable access to the pptpd dameon:
   ufw allow 1723
4. Enable ufw:
   ufw enable
5. Add an aliased network interface card (eth0:0): (We use the address space of 192.168.88.0/24 since its usually free for most networks for most users. You can feel free to change this address if it is already taken)
   Edit /etc/network/interfaces:
   nano /etc/network/interfaces

   Enter the following text at the end of the file:

   auto eth0:0
   iface eth0:0 inet static
   address 192.168.88.1
   netmask 255.255.255.0
   gateway (same value as listed for eth0)
   dns-nameservers (same value as listed for eth0)

   Replace the value of “gateway” with the same value you will see in this file for “eth0″, the real public network interface.
   Replace the value of “dns-nameservers” with the same value you will see in this file for “eth0″

6. Configure the pptpd daemon:
   Edit /etc/ppp/pptpd-options:
   nano /etc/ppp/pptpd-options

   Comment out (add a “#” char at the start of the line) the following lines:
   “refuse-pap”
   “refuse-chap”
   “refuse-mschap”
   “refuse-mschap-v2″
   “require-mppe-128″

   replace “#ms-dns 10.0.0.1″ with “ms-dns 8.8.8.8″
   replace “#ms-dns 10.0.0.2″ with “ms-dns 4.4.4.4″

   The last 2 lines above sets the DNS server the devices connecting to your PPTP VPN will use. The addresses above are for the Google Public DNS server, but can be any other DNS server (including the same DNS servers as Rackspace or your hosting provider use)

   Edit /etc/pptpd.conf :

   nano /etc/pptpd.conf

   Add at the bottom of the file:

   localip 192.168.88.1
   remoteip 192.168.88.2-20

   The value of “remoteip” will be the set of IP addresses the devices connecting to the VPN will get upon successful connection. Currently, we have here 18 addresses, which is enough for 18 concurrent devices. You can make this range bigger if needed.

7. Configure the username and password that will be used to authenticate client accessing the VPN:
   Edit /etc/ppp/chap-secrets:
   nano /etc/ppp/chap-secrets
   # client server secret IP addresses
   [UserName] pptpd [Password] *

   Replace [UserName] with the username you wish to use.
   Replace [Password] with the password you wish to use (I suggest a long random password. Try this generator)

8. Enable IP forwarding in the kernel:
   Edit /etc/sysctl.conf :
   nano /etc/sysctl.conf

   Uncomment the line “net.ipv4.ip_forward=1″
   For IPv6, uncomment “net.ipv6.conf.all.forwarding=1″

9. Enable IP forwarding in ufw:
   Edit /etc/default/ufw:
   nano /etc/default/ufw

   Change the value of “DEFAULT_FORWARD_POLICY” from “DROP” to “ACCEPT”

10. Add IP masquerading rule in ufw, so that NAT will work and devices connecting to the VPN will be seen as if the traffic goes out of the VPN server:
    Edit /etc/ufw/before.rules:
    nano /etc/ufw/before.rules

    Paste the text below after the header and before the “*filter” rules:

    # nat Table rules
    *nat
    :POSTROUTING ACCEPT [0:0]

    # Allow forward traffic from eth0:0 to eth0
    -A POSTROUTING -s 192.168.88.0/24 -o eth0 -j MASQUERADE

    # don’t delete the ‘COMMIT’ line or these nat table rules won’t be processed
    COMMIT

11. Reboot the machine, cross your fingers and hope for the best :-)

Configuring your iPhone / iPad

1. In your iPhone / iPad go to “Settings” -> “General” -> “Network” -> “VPN”
   
2. Select “Add VPN Configuration”
3. Select “PPTP”
4. In “Description” enter the name of the VPN connection
5. In “Server” enter the IP address of the server (or a server name, if you mapped the server’s IP address to a domain name)
6. In “Account” enter the username you have entered into the “/etc/ppp/chap-secrets” file
7. In “Password” enter the password you entered for the above username in “/etc/ppp/chap-secrets”
8. Make sure “Send All Traffic” is turned to “ON”
9. Set “Encryption Level” to “None” (this is how we configured the PPTP server in this post, if you setup an encryption try to keep it in “Auto”
10. Select save

This will revert to use the older hashing method instead of the newer “critbit” that was first introduced in version 2.1.

You can read a little bit more about it on the Yedda Dev Blog.

At my day job we use Disco, a Python + Erlang based Map-Reduce framework, to crunch our web servers and application logs to generate useful data.

Each web server log file per day is a couple of GB of data which can amount to a lot of log data that needs to be processed on a daily.

Since the files are big it was easier for us to perform all the necessary filtering of find the rows of interest in the “map” function. The problem is, that it requires us to return some generic null value for rows that are not interesting for us. This causes the intermediate files to contains a lot of unnecessary data that has the mapping of our uninteresting rows.

To significantly reduce this number, we have started to use the “combiner” function so that our intermediate results contains an already summed up result of the file the node is currently processing that is composed only from the rows we found interesting using the filtering in the “map” phase.

For example, if we have 1,000 rows and only 200 answer a certain filtering criteria for a particular report, instead of getting 1,000 rows in the intermediate file out of which 800 have the same null value, we now get only 200 rows.

In some cases we saw an increase of up to 50% in run time (the increase in speed is the result of reducing less rows from the intermediate files), not to mention a reduction in disk space use during execution due to the smaller intermediate files.

That way, we can keep the filtering logic in the “map” function while making sure we don’t end up reducing unnecessary data.

IEs4Linux 2 is developed to be used with recent Wine versions (0.9.x). It seems that you are using an old version. It’s recommended that you update your wine to the latest version (Go to: winehq.com).

In my case it showed the above text, which seems to be a warning, and run the UI but then got stuck and didn’t complete anything.

To overcome this issue simply run the installation without the GTK based UI in a terminal window:

./ies4linux –no-gui

That’s it. Works like a charm.

Just run the dev server under python 2.5 (i.e. python2.5 dev_appserver.py)

Windows cannot connect to the printer. Operation could not be completed (error 0x000006d1).

And you have a Samba server (version 3.0 and above) consider using the following technique to add the printer:

• Add a local printer (not a network one!)
• Select “create a new port”
• Select “Local port” as type of port
• In the port name enter the printer’s SMB path, i.e. \\sambaserver\printer_name
• Select the right driver

That’s all. Works like a charm!

If you have an older version of Samba (< 3.0) know that Vista uses NTLMv2 by default. Follow these instructions to revert back to NTLMv1 by default (also true for regular shares).

Also note that since this is a local printer that prints to a print queue on the Samba server, you might not be able to delete print jobs that were completely sent to the Samba server print queue, since we essentially created a local queue.

“Unable to retrieve MSN Address Book”

After searching a bit I found this post by Gijs Nelissen which said to use a different MSN plugin for Pidgin called msn-pecan.

I’ll reiterate the instructions for those with Ubuntu / Debian:

1. Close Pidgin (make sure the process is really down)
2. Run “apt-get install msn-pecan”
3. Start pidgin
4. Change your MSN account type from MSN to WLM
5. Reconnect

I don’t know if this error affects other libpurple based multi-headed IMs (such as Adium) (UPDATE: It appears this IS a libpurple issue – so Adium IS affected), however, the msn-pecan project has a Windows binary release as well as source release (if you care/need/want to compile it for Mac OS X or other Linux distributions).

Failed to run /usr/sbin/synaptic
Unable to copy the user’s Xauthorisation file.

Make sure to that you have enough space in your /tmp directory.

To check if that is indeed the problem run the following command in your terminal:

df -h

This command will show you each mounted volumes you may have including the one mounted to /tmp.

/tmp usually contains temporary data for applications while they run. It sometimes may reach a point where it 100% full (might have happened to me while I upgraded to Hardy Heron 8.04).

To clear /tmp run the following commands (BE CAREFUL NOT TO RUN rm -rf ON ANYWHERE OTHER THAN /tmp):

cd /tmp

pwd   # just to make sure you are really in /tmp

rm -rf *

I tried using its built-in install script on a vanilla Ubuntu Server 7.04 (a.k.a Feisty Fawn) and it worked flawlessly.

Aside from certain libraries which it needs to compile the vmmon and vmnet kernel modules (the installation script will tell you which ones are missing and you can get them from the repositories using apt-get), you’ll also need to install xinetd.

All in all, the installation script did all the job and it works fine without patching the vmmon code.

Keep up the good work VmWare Team!

Basically, if you encounter authentication problems at the Server’s Console after installing the VmWare server and until this bug is fixed, you need to edit /etc/pam.d/vmware-authd to contain:

#%PAM-1.0
auth required pam_unix_auth.so shadow nullok
account required pam_unix_acct.so

Afterwards, restart the VmWare service and try to authenticate using the server’s console again.

I’m just being the Good SEO Samaritan and bumping this article’s SEO so everyone will see it first (instead of it being buried down somewhere and the search results) :-) .