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December 2009

(Nerd) How to: Reconfigure SSH listening port on Ubuntu 9.10

1) Make sure that you have have ssh installed on your system.

sudo apt-get install openssh-server openssh-client

2) Open the sshd_config file using VI

sudo vi /etc/ssh/sshd_config

3) Here is the file in its entirety that was created by the installation process

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# Package generated configuration file
# See the sshd(8) manpage for details
 
# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
#ListenAddress 0.0.0.0
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes
 
# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 768
 
# Logging
SyslogFacility AUTH
LogLevel INFO
 
# Authentication:
LoginGraceTime 120
PermitRootLogin yes
StrictModes yes
 
RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile	%h/.ssh/authorized_keys
 
# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes
 
# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no
 
# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no
 
# Change to no to disable tunnelled clear text passwords
#PasswordAuthentication yes
 
# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
 
# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes
 
X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no
 
#MaxStartups 10:30:60
#Banner /etc/issue.net
 
# Allow client to pass locale environment variables
AcceptEnv LANG LC_*
 
Subsystem sftp /usr/lib/openssh/sftp-server
 
UsePAM yes

4) But we are mainly concerned with this part right here

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# Package generated configuration file
# See the sshd(8) manpage for details
 
# What ports, IPs and protocols we listen for
Port 22
 
...

5) Change the default port that is currently 22, to a non standard port. I changed mine to 22999

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# Package generated configuration file
# See the sshd(8) manpage for details
 
# What ports, IPs and protocols we listen for
Port 22999
 
...

6) Write/Quite so that you can save the changes to the file.

7) Now, all we have to do is restart the ssh daemon and it will listen from the new port.

sudo /etc/init.d/ssh restart

8 ) Finally, from another linux (or whatever OS you prefer) box, use the SSH client and login to your newly reconfigured server. Make sure to change the port using the ‘-p’ flag.

Example: ssh YOUR_USERNAME@IP_ADDRESS_OF_SERVER -p 22999

ssh jaredfolkins@192.168.1.107 -p 22999

The intuition of Benford

Have you heard of Dr. Benford? What’s that you say? You haven’t? Well don’t worry you are not alone. Most people haven’t heard of the guy either, but it would be my advice to most anyone (especially business owners) to Google him.

You see back in the 1930s, Frank Benford was working away as a physicist. And being a physicist, he had to use a lot of math. And for the simple math, he would look up the answers in what is known as a book of log tables. (Now days we would just use a calculator but obviously it had yet to be invented)

For example, this could be how the book was laid out.

Pages 001-100 dealt with math problems starting with the number #1
Pages 101-200 dealt with math problems starting with the number #2
Pages 201-300 dealt with math problems starting with the number #3
Pages 301-400 dealt with math problems starting with the number #4
Pages 401-500 dealt with math problems starting with the number #5
Pages 501-600 dealt with math problems starting with the number #6
Pages 601-700 dealt with math problems starting with the number #7
Pages 701-800 dealt with math problems starting with the number #8
Pages 801-900 dealt with math problems starting with the number #9

Anyway, after several years of work, he started to notice something. Benford noticed that he used the pages at the front of the book a lot more than the ones at the back. Which means that he was doing the majority of his work with numbers that began with either 1,2, or 3. And this troubled him.

Am I a bad physicist? He thought. Am I only using a subset of the tools that are available?

And after several years of statistical work, Benford came to the conclusion that numbers seemed to form a pattern in most (but not all) logarithmic systems.

Numbers that began with #1 were used 30.1% of the time
Numbers that began with #2 were used 17.6% of the time
Numbers that began with #3 were used 12.5% of the time
Numbers that began with #4 were used 9.7% of the time
Numbers that began with #5 were used 7.8% of the time
Numbers that began with #6 were used 6.7% of the time
Numbers that began with #7 were used 5.8% of the time
Numbers that began with #8 were used 5.1% of the time
Numbers that began with #9 were used 4.6% of the time

Now, I know what you are thinking.

Jared, what the hell does this have to do with me?

And so here it is, in two words. Fraud detection.

That’s right, you can apply Benford’s law to most anyone’s financial books, and it will help detect if fraud is taking place.

Really?

Yes really! Take this little nugget from Wikipedia.

In 1972, Hal Varian suggested that the law could be used to detect possible fraud in lists of socio-economic data submitted in support of public planning decisions. Based on the plausible assumption that people who make up figures tend to distribute their digits fairly uniformly, a simple comparison of first-digit frequency distribution from the data with the expected distribution according to Benford’s law ought to show up any anomalous results.[5] Following this idea, Mark Nigrini showed that Benford’s law could be used as an indicator of accounting and expenses fraud.[6]

In the United States, evidence based on Benford’s law is legally admissible in criminal cases at the federal, state, and local levels.[7]

Benford’s law has been invoked as evidence of fraud in the 2009 Iranian elections.[8]

Pretty cool right? And please keep in mind, this is just one of many tools available to detect fraud. But for someone like myself who is responsible for large Oracle databases that process millions and millions of financial transactions a year, it is really nice to be able to use Benford’s law. It won’t actually solve any issues, but it will help raise those needed RED FLAGS. Not to mention the nerd in me had a lot of fun writing the algorithm :-)

So, to all you business owners who worry that someone is screwing with your money, it may be helpful to apply Benford’s law to your books, and see what pops up.

For the record, this it not legal advice, plus my field is computer science so this is more of a nerd out topic for me.

And here is a book with interesting information that I enjoyed reading (link)

Radiolab recently did a story on Math featuring Benford’s law (link)

(Nerd) How to: Create a DSL (damn small linux) bootable usb thumb drive using Ubuntu 9.10

You will need to download the latest .iso from the Damn Small Linux site.

Also, I am running ubuntu 9.10 as my host OS but you should be able to run any linux/unix operating system and the commands should work.

1) Plug in your usb device.

2) Next, open up the terminal application and enter the following command. By issuing sudo -i command, you are assuming the identity of root for the rest of the session.

sudo -i

3) Run the fdisk -l command to look at the devices installed on your system.

root@jetBook:~# fdisk -l

4) My output is posted below.

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x355aa9d3
 
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1        9407    75561696    7  HPFS/NTFS
/dev/sda2            9408       18813    75553695    5  Extended
/dev/sda3           18814       19451     5124735   1c  Hidden W95 FAT32 (LBA)
/dev/sda4           19452       19457       48195   ef  EFI (FAT-12/16/32)
/dev/sda5            9408       18039    69336508+  83  Linux
/dev/sda6           18040       18813     6217123+  82  Linux swap / Solaris
 
Disk /dev/sdb: 4047 MB, 4047502848 bytes
4 heads, 32 sectors/track, 61759 cylinders
Units = cylinders of 128 * 512 = 65536 bytes
Disk identifier: 0x00000000
 
   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1       61759     3952560    b  W95 FAT32

First you will notice my internal hard drive and the several partitions that are written on it.

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x355aa9d3
 
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1        9407    75561696    7  HPFS/NTFS
/dev/sda2            9408       18813    75553695    5  Extended
/dev/sda3           18814       19451     5124735   1c  Hidden W95 FAT32 (LBA)
/dev/sda4           19452       19457       48195   ef  EFI (FAT-12/16/32)
/dev/sda5            9408       18039    69336508+  83  Linux
/dev/sda6           18040       18813     6217123+  82  Linux swap / Solaris

5) We are primarily concerned about the following segment.

Disk /dev/sdb: 4047 MB, 4047502848 bytes
4 heads, 32 sectors/track, 61759 cylinders
Units = cylinders of 128 * 512 = 65536 bytes
Disk identifier: 0x00000000
 
   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1       61759     3952560    b  W95 FAT32

6) Since I only have two drives installed on my system (Internal HD, and USB thumb drive) we can logically deduce that /dev/sdb is the thumb drive, and for several reasons. The primary one being that I am using a 4GB drive, and the output next to /dev/sdb shows the total amount of memory.

Disk /dev/sdb: 4047 MB

7) Unmount the /dev/sdb1 partition

root@jetBook:~# umount /dev/sdb1

8 ) Run the following command

root@jetBook:~# fdisk /dev/sdb

Which will produce this prompt.

Command (m for help):

9) Delete any existing partitions.

Command (m for help): d
Selected partition 1

9a) Please note, you may get a prompt asking you for a number selection (1-4). You will need to keep going through this step in order to delete ALL of the existing partitions on the usb device. Example below assumes there are two partitions on the usb device.

Command (m for help): d
Partition number (1-4): 1
 
Command (m for help): d
Selected partition 2

10) Once the partition(s) are deleted, create a new one. Type the letter ‘n’ and press return. ‘n’ is for “New” partition.

Command (m for help): n

***) Enter the letter ‘p’ for primary and press return.

Command action
   e   extended
   p   primary partition (1-4)
p

11) Select number ‘1’ for the partition number definition.

Partition number (1-4): 1

12) Enter ‘1’ to designate the first cylinder.

First cylinder (1-61759, default 1): 1

13) Enter the large default number so that we can use the entire disk. In my case, the ending cylinder number is 61759.

Last cylinder, +cylinders or +size{K,M,G} (1-61759, default 61759): 61759

14) Make the drive bootable

Command (m for help): a
Partition number (1-4): 1

15) Show the definition table by entering the letter ‘p’ from the prompt. This is to make sure there is an asterisk under the ‘boot’ column.

Command (m for help): p
 
Disk /dev/sdb: 4047 MB, 4047502848 bytes
4 heads, 32 sectors/track, 61759 cylinders
Units = cylinders of 128 * 512 = 65536 bytes
Disk identifier: 0x00000000
 
   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1       61759     3952560   83  Linux

16) Write the changes to the disk by entering the letter ‘w’

Command (m for help): w
The partition table has been altered!

16a) Note: you may get the following error. Don’t worry, it is not a big deal but it does mean you probably didn’t correctly unmount the device in step (STEP #7).

Calling ioctl() to re-read partition table.
 
WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.

If this happens, it is now like a choose your own adventure book. You can…

  • Start over
  • Go back to step #7
  • Or remember that things may be screwed up, and proceed just to see if you can

Choose wisely…

17) Format the disk using ext2. !!!WARNING!!! if you mess this up, you can easily format the root partition of YOUR internal hard drive.

root@jetBook:~# mke2fs /dev/sdb1

Which will produce the following output.

mke2fs 1.41.9 (22-Aug-2009)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
247008 inodes, 987989 blocks
49399 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=1015021568
31 block groups
32768 blocks per group, 32768 fragments per group
7968 inodes per group
Superblock backups stored on blocks:
	32768, 98304, 163840, 229376, 294912, 819200, 884736
 
Writing inode tables: done
Writing superblocks and filesystem accounting information: done
 
This filesystem will be automatically checked every 28 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

18) Make a usb directory inside /mnt

NOTE: if you are using a different flavor of linux/unix you will have to adjust the tutorial accordingly.

root@jetBook:~# mkdir /mnt/usb

19) mount the usb thumb drive partition to the newly created directory. In my case it is the 1st partition, sdb1.

root@jetBook:~# mount /dev/sdb1 /mnt/usb

20) Create an iso directory to eventually mount the dsl-4.4.10.iso

root@jetBook:/# mkdir /mnt/iso

21) Find the directory where your damn small linux .iso file exists. Since I used firefox3.5 to download the .iso, my file is in the ‘Downloads’ directory.

/home/YOUR_USERNAME/Downloads

22) Mount the .iso to the directory. Conceptually, this allows you access to the files stored in the .iso as if it were a common directory on your file system.

root@jetBook:# mount -o loop /home/YOUR_USERNAME/Downloads/dsl-4.4.10.iso /mnt/iso

23) Copy all the files from /mnt/iso into /mnt/usb. We issue the ‘-p’ flag so that we keep the existing permissions. We issue the ‘-R’ flag so the the copy is recursive.

root@jetBook:# cp -pR /mnt/iso/* /mnt/usb

24) Install grub into the boot block of /dev/sdb.

root@jetBook:# grub-install --no-floppy --root-directory=/mnt/usb /dev/sdb

25) You should get the following output.

Probing devices to guess BIOS drives. This may take a long time.
Installing GRUB to /dev/sdb as (hd1)...
Installation finished. No error reported.
This is the contents of the device map /mnt/usb/boot/grub/device.map.
Check if this is correct or not. If any of the lines is incorrect,
fix it and re-run the script `grub-install'.
 
(hd0)	/dev/sda
(hd1)	/dev/sdb

26) Create the file menu.lst in the /mtn/usb/boot/grub/ folder.

root@jetBook:/# vi /mnt/usb/boot/grub/menu.lst

28) Here is the contents of my menu.lst file and you are more than welcome to copy/paste the contents. There is one issue though, your hardware may not lay itself out like mine, so some further troubleshooting may be involved.

title Damn Small Linux
root (hd0,0)
kernel /boot/isolinux/linux24 root=/dev/sda1 ro lang=us toram noeject frugal
initrd /boot/isolinux/minirt24.gz
boot
EOF

29) At this point, you should be able to issue the following four commands in order to cleanup your file system

root@jetBook:# umount /mnt/iso
root@jetBook:# umount /mnt/usb
root@jetBook:# rm -R /mnt/usb
root@jetBook:# rm -R /mnt/iso

And from here on, it is all you. Just reboot your machine, and go into your BIOS in order to make sure you are booting from the usb device.

Please understand, in step #28 where you potentially copy/paste my ‘menu.lst’ settings, it is an area where you could run into problems. I will try and cover some information on the GRUB boot loader eventually. Because GRUB seems to mistify so many people, yet it is incredibly powerful.

(Nerd) Error: Unable to install Fedora 12 on a VMware Fusion Virtual Machine

I tried to install an instance of Fedora 12 on a virtual machine using VMware Fusion. I used the virtual machine to boot from the .iso and it took me to the Graphical installation. Unfortunately when I double clicked the icon to install, nothing would happen.

fedora12_install

Some simple troubleshooting follows.

Right clicked on ‘install to Hard Drive’ icon and selected properties.

install_to_harddrive_properties

Looked at the path of the application

liveinst_path

Closed the ‘Install to Hard Drive Properties’ window, and opened up a terminal session

fedora_terminal

Ran the following command

/usr/bin/liveinst

It gave me an error concerning ‘/media/*: not found’ and then it  showed me the real issue.

You do not have enough RAM to use the graphical installer.

fedora_no_memory

So I went looking for the minimum requirements and found this from Fedora’s site.

1.2.2. Processor and memory requirements for x86 Architectures

The following CPU specifications are stated in terms of Intel processors. Other processors, such as those from AMD, Cyrix, and VIA that are compatible with and equivalent to the following Intel processors, may also be used with Fedora. Fedora 12 requires an Intel Pentium Pro or better processor, and is optimized for i686 and later processors.

Recommended for text-mode: 200 MHz Pentium Pro or better
Recommended for graphical: 400 MHz Pentium Pro or better
Minimum RAM for text-mode: 128 MiB
Minimum RAM for graphical: 192 MiB
Recommended RAM for graphical: 256 MiB

I know that my Virtual Machine was setup for 256mb of RAM but I guess that wasn’t enough

SOLUTION: I powered down my virtual machine and increased the RAM to 512mb, rebooted, and the problem was solved.

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