Enable/Disable Output of Audio Input in Ubuntu

After hooking up my old-school turntable to the input jack on my desktop PC, I thought I’d be easily able to output the sound from my speakers. I could even see the audio playing as an input and could record it using Audacity, but not output it directly.

By default Ubuntu does not load the loopback module for Pulse, the audio manager for Ubuntu. You need to load this module to get the input audio to play out to your speakers. To enable this feature run the following command:

pactl unload-module module-loopback

This will load it one time, and when you reboot it will again be unloaded. To make it ‘stick’ and load on every boot, run this command:

sudo sh -c 'echo "load-module module-loopback" >> /etc/pulse/default.pa'

If you want to undo the loopback module, run this command:

pactl unload-module module-loopback

and to disable it from running on startup:

sudo sh -c 'sed -i "/load-module module-loopback/d" /etc/pulse/default.pa'

This was tested in Ubuntu 13.04.

If you start getting weird audio feedback after running this command, you might want to check that you didn’t accidentally load the loopback adapter twice!

Experimenting with Pascal on Ubuntu

I’ve been busy lately on a number of projects, one of which is a programming class I am currently taking. The class itself is interesting, we are learning about the different types of programming languages. For our latest project, we were tasked with writing a simple program in Pascal. Pascal isn’t used too much any more since it lacks some of the features that most modern languages have, but it is good to know at least a little bit about it in case you ever run across some old Pascal programs in the wild.

The syntax for pascal is a bit verbose, that is the main complaint about it. There are a number of others, but that is beyond the scope of this howto.

Installing The Pascal Compiler on Ubuntu

Installing Pascal in modern Ubuntu is a cinch. The Free Pascal Compiler, or fpc, is all that you need to get started. It works great on 32-bit or 64-bit systems. Install with:

sudo apt-get install fpc

Any prerequisites will automatically download and install along with fpc.

Getting Started in Pascal

To test the compiler let’s start with a simple Hello World program. Open up hello.pas and enter:

[cc lang=”pascal”]program Hello;


Writeln(‘Hello World’);

end. [/cc]

Compile with [cci]fpc hello.pas[/cci] and run:

dave@cerberus:~/Pascal$ ./hello
Hello World

Selection Sort in Pascal

Now that we’ve verified it is running, I’m going to show you the code that I wrote for my program. Basically we were asked to Selection Sort two arrays of varying length. Apparently one of the (bad) features of Pascal originally was that you needed to declare the length of the array which made it a pain to work with them.

In this situation it is just two arrays so it isn’t too bad. Enter your array by creating two text files arrayA.txt and arrayB.txt. One number per line. The source code for sort.pas is:

[cc lang=”pascal”]program Sort;

A: array[1..10] of Integer;
B: array[1..20] of Integer;
F: Text;
i,j,k,l,m,temp: Integer;

{Read in array A}
Assign(F, ‘arrayA.txt’);
i:= 0;
while not EOF(F) do begin
Read(F, A[i]);

{Read in array B}
Assign(F, ‘arrayB.txt’);
j:= 0;
while not EOF(F) do begin
Read(F, B[j]);

{Print out the unsorted arrays}
WriteLn(‘Unsorted Arrays:’);
WriteLn(‘Array A:’);
for k:=1 to i do
Write(A[k], ‘ ‘);
WriteLn(‘Array B:’);
for k:=1 to j do
Write(B[k], ‘ ‘);
WriteLn(‘Sorting Arrays…’);

{Selection Sort Array A}
for l := 1 to i do
for m := l + 1 to i do
if A[l] > A[m] then
temp := A[l];
A[l] := A[m];
A[m] := temp;
{Selection Sort Array B}
for l := 1 to j do
for m := l + 1 to j do
if B[l] > B[m] then
temp := B[l];
B[l] := B[m];
B[m] := temp;

{Print out the sorted arrays}
WriteLn(‘Selection Sorted Arrays:’);
WriteLn(‘Array A: ‘);
for k:=1 to i do
Write(A[k], ‘ ‘);
WriteLn(‘Array B: ‘);
for k:=1 to j do
Write(B[k], ‘ ‘);
end. [/cc]

Compile and run (ok to ignore the compile-time errors)

dave@cerberus:~/Pascal$ fpc sort.pas
Free Pascal Compiler version 2.4.0-2 [2010/03/06] for x86_64
Copyright (c) 1993-2009 by Florian Klaempfl
Target OS: Linux for x86-64
Compiling sort.pas
Linking sort
/usr/bin/ld: warning: link.res contains output sections; did you forget -T?
73 lines compiled, 0.1 sec
dave@cerberus:~/Pascal$ ./sort
Unsorted Arrays:
Array A:
28 24 85 55 43 6 23 13 59 71
Array B:
13 37 36 53 24 83 27 42 62 71 9 92 1 41 6 3 88 77 65 67
Sorting Arrays...
Selection Sorted Arrays:
Array A:
6 13 23 24 28 43 55 59 71 85
Array B:
1 3 6 9 13 24 27 36 37 41 42 53 62 65 67 71 77 83 88 92

And there you have it. Compiling Pascal program on Ubuntu is an easy way to get your feet wet in programming. Pascal is a great beginner’s programming language, but if you want to learn more there are a number of great resources available for learning Pascal.

UbunTOS – Ubuntu 9.10 + TinyOS 2.x VirtualBox Image

This is my admittedly minor but I hope useful contribution to the TinyOS development community. TinyOS is an Operating System and development framework for Wireless Sensor Networks and other platforms which has a small footprint and is very energy conscious.

The TinyOS source code is available for free online for many operating systems, however it takes a long time to get the environment set up and it is not portable at all. I came across XubunTOS but it did not seem to be in active development anymore, so I endeavored to install TinyOS 2.1 and 2.x from source into a regular Ubuntu image. The most help came from Matt Keally’s Blog. While doing this, I thought it might be useful to many others who wish to develop in the TinyOS framework but might not have the skills necessary to install it. Therefore, I developed this VirtualBox image so that you can install it on any system for which VirtualBox is available and supports USB passthrough for the programming of the motes. I’ve tested on Windows 7, Windows XP and it should work on any other host OS, but I would love to hear your feedback. All funny business aside, I present to the world UbunTOS: Read more

Tweaking TCP for Fast (100mbps+) Connections and Transfers on Linux

We recently did some speed testing on a few of the servers on our network, and we were not receiving the speeds expected considering they were sitting on a physical 100mbps ethernet port. The servers were indeed on physical 100mbps connection, however wget (TCP/IP, HTTP Port 80) download tests showed only a max of about 1.5MB/sec (note the 8bit/byte conversion, so this translates to about 12mbits).

This is due to how TCP frames data packets and optimizes them for connections. I believe by default TCP on most systems assumes about a 10mbit max capable transfer rate, so it does not show performance gains on a larger pipe without modification to the kernel options which govern TCP/IP frame size and features. Some distributions may make this change for you automatically however many will not.

To keep things short and sweet, we took the following advice from Speedguide.net on tweaking TCP parameters on linux kernel systems. This will cover Linux 2.1 and above – which means CentOS, RedHat, Ubuntu, Debian and many more distributions.

The TCP Parameters we will change are:

  • /proc/sys/net/core/rmem_max – Maximum TCP Receive Window
  • /proc/sys/net/core/wmem_max – Maximum TCP Send Window
  • /proc/sys/net/ipv4/tcp_timestamps – (RFC 1323) timestamps add 12 bytes to the TCP header…
  • /proc/sys/net/ipv4/tcp_sack – tcp selective acknowledgements.
  • /proc/sys/net/ipv4/tcp_window_scaling – support for large TCP Windows (RFC 1323). Needs to be set to 1 if the Max TCP Window is over 65535.

If you recall /proc/ is the volatile portion of kernel configuration, you can change it on the fly but it will be reset on reboot unless settings are changed via an init file or setting the options in /etc/sysctl.conf. To change the settings once (to test):

echo 256960 > /proc/sys/net/core/rmem_default
echo 256960 > /proc/sys/net/core/rmem_max
echo 256960 > /proc/sys/net/core/wmem_default
echo 256960 > /proc/sys/net/core/wmem_max
echo 0 > /proc/sys/net/ipv4/tcp_timestamps
echo 1 > /proc/sys/net/ipv4/tcp_sack
echo 1 > /proc/sys/net/ipv4/tcp_window_scaling

And to apply them for good, add the following lines to /etc/sysctl.conf:

net.core.rmem_default = 256960
net.core.rmem_max = 256960
net.core.wmem_default = 256960
net.core.wmem_max = 256960
net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_sack = 1
net.ipv4.tcp_window_scaling = 1

Use ‘sysctl -p’ to apply the changes in this file to your running Linux instance. Feel free to experiment with these numbers to see how they impact your transfers, it depends a lot on how many and how large the files are that you transferring. These changes must be made on the SERVER side, any change on the client side would not impact the download speed from the server.

There are several other variables to consider, and these all depend on your application so change them if you know what you are attempting to do. After changing these settings, you will see speeds of about 10MB/sec (80mbps) on a 100mbps connection. The other 20mbps are lost in TCP and other network layer overhead, which is unavoidable.

How To Reset Windows XP, Vista, Windows 7 Passwords with Ubuntu 9.10 Live Image and a USB Drive

I put this together for a project in a class I am taking, and thought it would be handy for others as well. The goal is to access a Windows filesystem and reset the password for a user, for example if someone forgot the Administrator password or the account is locked out from too many bad password login attempts. This works on all modern Windows Operating Systems: Windows 2000, 2003, XP, Vista, Win7 etc. Make sure to create a backup if you want to make sure you don’t corrupt your Windows install, as it can happen.

Tools used:

Accessing the Filesystem

First we use unetbootin to install Ubuntu 9.10 to a flash drive. The flash drive needs to be at least 1GB to install the image.

Unetbootin settings

Select “Diskimage” and then the .iso file we downloaded of the Ubuntu 9.10 image.

Select the USB Drive and Drive Letter to install the ISO onto. Click OK:

Unetbootin doing its thing

Once the program is done, click ‘exit’ and remove the USB Drive. You now have a bootable live image of Ubuntu 9.10.

Plug the usb drive into the target system. Boot off of the drive, you may need to change the boot options in the BIOS if it is set to boot off of the hard drive. Select “Default” in the unetbootin boot menu to boot into the Ubuntu OS. It will automatically log you in.

Once booted you already have access to the Windows filesystem since the ntfs filesystem driver is included in the kernel. This is nice and wasn’t the case not too long ago.

We chose two reasons to use unetbootin and Ubuntu 9.10. The first is the ease of use of installing a bootable image. After downloading the two packages, it is trivial to load the OS onto the drive, and since it includes ntfs drivers it allows us to access the unencrypted hard drive on boot. Since it is on a USB drive, any system made since 2000 or so should be able to boot this. You don’t need to lug around a CD or even access the CD drive.

To prevent easy access to the hard drive, encryption of the hard drive partition would be necessary using Microsoft EFS or TrueCrypt hard drive encryption software. After encrypting the hard drive, any live operating system running would not be able to decrypt the hard drive easily.

Furthermore, installation of a BIOS level password would ensure that any unauthorized users would not be able to boot alternative operating systems via USB, CDROM, Floppy or other method. The only way to defeat a BIOS level password would be to reset the BIOS (requiring entrance into the hardware of the system) or using an Evil Maid style attack.

The Evil Maid attack is performed by a theoretical malicious party that has access to the target PC without alerting the legitimate user. Without knowledge of the authorized; a root kit or device would be installed (for example, on the USB connector of the keyboard) to sniff out the password as entered on bootup. After the user boots the system and finishes her work, ostensibly shutting down the system securely, at least to her knowledge, the Evil Maid would then collect the password entered into the BIOS, thereby defeating the BIOS password security measure.

Resetting the Password

We can now reset the Administrator or any other password on this system using the tool chntpw. To install this package, ensure the system has a connection to the internet (via dhcp perhaps?) and run the command:

sudo software-properties-gtk --enable-component=universe --enable-component=multiverse; sudo apt-get update; sudo apt-get install chntpw

Alternatively, you can download the executable and place it on the USB drive to give access without connecting to the internet. chntpw is the software that modifies the SAM (Security Accounts Manager) database file. Use the terminal to change directories to the password file

cd /media/path/to/disk/WINDOWS/system32/config/

Then execute the chntpw utility:

  # sudo chntpw -u username SAM SYSTEM

View the sample output:

ubuntu@ubuntu:/media/B830C9BC30C981BC/WINDOWS/system32/config$ sudo chntpw SAM SECURITY
chntpw version 0.99.5 070923 (decade), (c) Petter N Hagen
Hive <SAM> name (from header): <\SystemRoot\System32\Config\SAM>
ROOT KEY at offset: 0x001020 * Subkey indexing type is: 666c <lf>
Page at 0x7000 is not 'hbin', assuming file contains garbage at end
File size 262144 [40000] bytes, containing 6 pages (+ 1 headerpage)
Used for data: 255/20736 blocks/bytes, unused: 9/3648 blocks/bytes.

Hive <SECURITY> name (from header): <emRoot\System32\Config\SECURITY>
ROOT KEY at offset: 0x001020 * Subkey indexing type is: 666c <lf>
Page at 0xe000 is not 'hbin', assuming file contains garbage at end
File size 262144 [40000] bytes, containing 13 pages (+ 1 headerpage)
Used for data: 1074/49024 blocks/bytes, unused: 9/3808 blocks/bytes.

* SAM policy limits:
Failed logins before lockout is: 0
Minimum password length        : 0
Password history count         : 0
| RID -|---------- Username ------------| Admin? |- Lock? --|
| 01f4 | Administrator                  | ADMIN  | dis/lock |
| 03ec | ASPNET                         |        | dis/lock |
| 03ed | CSC603                         | ADMIN  | dis/lock |
| 01f5 | Guest                          |        | dis/lock |
| 03e8 | HelpAssistant                  |        | dis/lock |

---------------------> SYSKEY CHECK <-----------------------
SYSTEM   SecureBoot            : -1 -> Not Set (not installed, good!)
SAM      Account\F             : 1 -> key-in-registry
SECURITY PolSecretEncryptionKey: 1 -> key-in-registry

***************** SYSKEY IS ENABLED! **************
This installation very likely has the syskey passwordhash-obfuscator installed
It's currently in mode = -1, Unknown-mode
This program can change passwords even if syskey is on, however
if you have lost the key-floppy or passphrase you can turn it off,
but please read the docs first!!!

NOTE: On WINDOWS 2000 it will not be possible
to turn it on again! (and other problems may also show..)

NOTE: Disabling syskey will invalidate ALL
passwords, requiring them to be reset. You should at least reset the
administrator password using this program, then the rest ought to be
done from NT.

Do you really wish to disable SYSKEY? (y/n) [n]
RID     : 0500 [01f4]
Username: Administrator
comment : Built-in account for administering the computer/domain
homedir : 

User is member of 1 groups:
00000220 = Administrators (which has 2 members)

Account bits: 0x0210 =
[ ] Disabled        | [ ] Homedir req.    | [ ] Passwd not req. |
[ ] Temp. duplicate | [X] Normal account  | [ ] NMS account     |
[ ] Domain trust ac | [ ] Wks trust act.  | [ ] Srv trust act   |
[X] Pwd don't expir | [ ] Auto lockout    | [ ] (unknown 0x08)  |
[ ] (unknown 0x10)  | [ ] (unknown 0x20)  | [ ] (unknown 0x40)  | 

Failed login count: 1, while max tries is: 0
Total  login count: 1

- - - - User Edit Menu:
 1 - Clear (blank) user password
 2 - Edit (set new) user password (careful with this on XP or Vista)
 3 - Promote user (make user an administrator)
 4 - Unlock and enable user account [probably locked now]
 q - Quit editing user, back to user select
Select: [q] >

Depending on the status of the SYSKEY password security, you may only be able to blank the password and not actually change it. I recommend blanking the password and then resetting it once you log into the system.

You can also unlock a system if the user accounts have all been locked out due to too many login attempts or any other reason. Using these tools you can gain access to almost any unencrypted Windows system, from Windows NT up to Windows 7.

As a warning, If there is data on the hard drive you wish to keep, make sure to make a backup of the hard drive before performing this password as it can corrupt the Windows installation.

A Poor Man’s VPN: Proxy Web Connection to Remote Server (via SSH and Tunnel)

Did you ever have a situation where you needed to access a website that had an IP restriction in place? I recently had a situation where I needed to access the web via my university connection (due to IP restrictions placed on accessing databases of research papers). They do not have a VPN setup so it is hard to do this off-campus.

I do however have access to a linux machine on campus. I am familiar with port forwarding using SSH but I had never used it to actually tunnel web traffic using a web browser on Windows. Turns out it is surprisingly easy!

The ssh command to use is:

ssh -C2qTnN -D 8080 username@remote_host

This command sshes to the remote_host, and creates a tunnel on your localhost, port 8080. Note that you need to have private key authentication already set up for this host – it will not work with password authentication.

The description of the switches are (from the ssh man page):

  • -C : Compression
  • -2 : Use SSHv2
  • -q : quiet!
  • -T : Disable pseuto-tty allocation
  • -n : Prevents reading from stdin (you need to have private key authentication set up, to prevent password authentication)
  • -N : Do not execute a remote command (or launch a shell). Just use the ssh process for port forwarding
  • -D : Allocate a socket to listen on the local side. When a connection is made to this port it is located to the remote machine. Makes SSH work as a SOCKS server. Only root can forward privileged ports like this.

From here, you set up Firefox or your browser of choice to use a Socks proxy on localhost:8080. The man page says that SOCKS4 and SOCK5 should both work but I had to use SOCKS v4, SOCKS v5 did not seem to work for me.

Ubuntu Server in Place Network Upgrade From 8.10 to 9.04

Ubuntu Upgrade

It is easy to do an in-place upgrade of Ubuntu Server from 8.10 ‘Intrepid Ibex‘ to 9.04 ‘Jaunty Jackalope‘. You can do this remotely over ssh or whatever you use to control your server. Best practices say to make sure to backup your server before doing the upgrade. I’ve done several servers this way with no issues!

Issue the command:

sudo apt-get update; sudo apt-get upgrade; sudo apt-get install update-manager-core; sudo do-release-upgrade

Follow any prompts to first upgrade the current distribution with the newest packages, then do the release upgrade.