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tutorial - History of Unix-like operating systems showing Linux's origins

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source:http://linuxpoison.blogspot.com/2009/06/135781757115184.html

tutorial - Block ssh brute force attack on OpenSuSe

A brute force attack consists of trying every possible code, combination, or password until you find the right one.

As an example, imagine a system which only allows 4 digit PIN codes. This means that there are a maximum of 10,000 possible PIN combinations.

From the example above, PIN security could be increased by:
    * Increasing the length of the PIN
    * Allowing the PIN to contain characters other than numbers, such as * or #
    * Imposing a 30 second delay between failed authentication attempts
    * Locking the account after 'x' failed authentication attempts

Will try to implement the option #3 & #4 in OpnSuSe using SuSEfirewall
open your favorite editor and edit file: /etc/sysconfig/SuSEfirewall2:

# Add the following rule
FW_SERVICES_ACCEPT_EXT="0.0.0.0/0,tcp,22,,hitcount=3,blockseconds=60,recentname=ssh"

# Now Restart firewall:
rcSuSEfirewall2 restart

Now attacker will just have 3 attempts to break in.

I hope this tutorial has been useful for you too! If you've enjoyed this post, please consider subscribing to Linuxpoison for future updates and more.

source:http://linuxpoison.blogspot.com/2009/06/13578175719873.html

tutorial - How to calculates CRC checksum and the byte count for file(s)

cksum prints the CRC checksum for each file along with the number of bytes in the file, and the file name unless no arguments were given.

cksum is typically used to ensure that files transferred by unreliable means have not been corrupted, by comparing the cksum output for the received files with the cksum output for the original files (typically given in the distribution).

The CRC algorithm is specified by the POSIX standard. It is not compatible with the BSD or System V sum algorithms and cksum is more robust.

The only options are --help and --version.
An exit status of zero indicates success, and a nonzero value indicates failure.

Example of using cksum:
Create file with following text:

$ echo "Open source is a development method for software that harnesses the power of distributed peer review and transparency of process." > file.txt

$ cksum file.txt
1121778036 130 file.txt

Here cksum calculate a cyclic redundancy check (CRC) of given file (file.txt). Users can check the integrity of file and see if the file has been modified. use your favorite text editor and remove a "." from the end of the sentence and run cksum again on the same file and observe the difference in the output

$ cksum file.txt
2131559972 129 file.txt

Another Example:
cksum can be also be used for checking the bunch of files, first get the checksum of the entire files withing the directory
$ cksum * > /someother/location/cksum.list
Above command generates checksums' file.

Now after transferring the files, run the cksum command on the same sets of file to get the new chksum figure and finally compare these two values to figure out if the files are been tempered or not.

$ cksum * > /someother/location/cksum.list-2
$ diff cksum.list cksum.list-2

cksum also can be used for fast searching for duplicates.

$ cksum *

source:http://linuxpoison.blogspot.com/2009/06/13578175715695.html

tutorial - Archiving, Encryption and File split tool - PeaZip

PeaZip is a cross-platform portable file archiver, released under LGPL.

PeaZip supports many different archive and compression formats including: 7z, 7z-sfx, ARC/WRC, BZ2, GZ, LPAQ, PAQ, PEA, QUAD, split, TAR, UPX, ZIP; Read: 7Z, ARC/WRC, ACE, ARJ, BZ2/TBZ2, CAB, CHM, CPIO, DEB, GZ/TGZ, ISO, JAR/EAR/WAR, LZH, NSIS, OOo, PAK/PK3/PK4, PAQ, PEA, PET/PUP, QUAD, RAR, RPM, SLP, split, TAR, U3P, WIM, XPI, Z/TZ, and ZIP/SMZIP.

PeaZip is developed in FreePascal using the Lazarus development environment.
PeaZip can be easily integrated with GNOME and KDE.

Features include:
    * Volume spanning
    * Compression
    * Authenticiated encrpytion
          o 7Z, with AES256 encryption
          o ARC, with AES256, Blowfish, Twofish256 and Serpent256 encryption
          o PEA, with AES256 authenticated encryption (EAX mode)
          o ZIP with WinZip's AE encryption based on AES256
          o ARC format protects archives against corruption employing recovery records
    * Edit, save and restore archive layouts
    * Apply multiple filters to archive contents
    * Handle multiple archives simultaneously
    * Split/join files
    * Wipe files (secure deletion
    * Compare, checksum and has files
    * System benchmark
    * Generate random passwords and key files

Installation of PeaZip:
PeaZip for openSUSE (PackMan)
PeaZip for Mandriva (MIB Mandriva Italia Backports)
Ubuntu/Debian (DEB)
Fedora (rpm)

After successful installation of PeaZip go to console and type command: peazip to open up the application

source:http://linuxpoison.blogspot.com/2009/06/135781757117136.html

tutorial - DenyHosts Installation and Configuration on OpenSuSe

DenyHosts is a script intended to be run by Linux system administrators to help thwart SSH server attacks (also known as dictionary based attacks and brute force attacks).

If you've ever looked at your ssh log (/var/log/secure on Redhat, /var/log/messages on OpenSuSe, etc...) you may be alarmed to see how many hackers attempted to gain access to your server. Hopefully, none of them were successful (but then again, how would you know?). Wouldn't it be better to automatically prevent that attacker from continuing to gain entry into your system?

DenyHosts attempts to address the above... and more by by monitoring invalid login attempts in the authentication log and blocking the originating IP addresses, adding entries to /etc/hosts.deny. DenyHosts will also inform Linux administrators about offending hosts, attacked users and suspicious logins.

Features include:
    * Parses authentication log to find all login attempts and filters failed and successful attempts
    * Synchronization mode allows DenyHosts daemons the ability to share data via a centralized server to proactively thwart attacks
    * DenyHosts Can be run from the command line, cron or as a daemon
    * Records all failed login attempts for the user and offending host
    * For each host that exceeds a threshold count, records the evil host
    * Keeps track of each non-existent user when a login attempt failed
    * Keeps track of each existing user (eg. root) when a login attempt failed
    * Keeps track of each offending host
    * Keeps track of suspicious logins (that is, logins that were successful for a host that had many login failures)
    * Keeps track of the file offset, so that you can reparse the same file (/var/log/secure) continuously (until it is rotated).
    * When the log file is rotated, the script will detect it and parse from the beginning
    * Appends /etc/hosts.deny and adds the newly banned hosts
    * Optionally sends an email of newly banned hosts and suspicious logins
    * Keeps a history of all user, host, user/host combo and suspicious logins encountered which includes the data and number of corresponding failed login attempts
    * Maintains failed valid and invalid user login attempts in separate files, such that it is easy to see which valid user is under attack (which would give you the opportunity to remove the account, change the password or change it's default shell to something like /sbin/nologin
    * Upon each run, the script will load the previously saved data and re-use it to append new failures
    * Resolves IP addresses to hostnames, if available
    * /etc/hosts.deny entries can be expired (purge) at a user specified time

Installation: Use "1-click" installer to install DenyHosts
OpenSuSe 11.1 - Install DenyHosts
OpenSuSe 11.0 - Install DenyHosts

Configuration of Denyhosts:
You can find the main configuration: /etc/denyhosts.conf where most of the settings are good for any normal operation of DenyHosts but you can also tweak it more to suite your needs. look into the comments in this file to know more about the configuration details

Few other important setting:

# vi /var/lib/denyhosts/allowed-hosts
# vi /etc/hosts.allow

you'll want to add in these 2 files the IP(s) you will use to connect to your system that's running Denyhosts so that you aren't inadvertently denied access to your own system(s).

Starting the service and marking it to run on each system reboot:
# service denyhosts start; chkconfig --level 2345 denyhosts on

source:http://linuxpoison.blogspot.com/2009/06/13578175713887.html

tutorial - Complete and Reliable Password Manager for OpenSuSe - KeepassX

KeePassX is a password manager or safe which helps you to manage your passwords in a secure way. You can put all your passwords in one database, which is locked with one master key or a key-disk.

This means that you only have to remember one single master password or insert the key-disk to unlock the whole database. The complete database is always encrypted either with AES (alias Rijndael) or Twofish encryption algorithm using a 256 bit key. Therefore the saved information can be considered as quite safe.

KeePassX offers a little utility for secure password generation. The password generator is very customizable, fast and easy to use. Especially someone who generates passwords frequently will appreciate this feature.

Installation of KeePassX: use "1-click" installer to install KeePassX
OpenSuSe 11.1 - install KeePassX
OpenSuSe 11.0 - install KeePassX

After successful installation go to command prompt and type command: keepassx to start the application, now go to File menu and create a new database to store the information, here you also have to provide your master key to open/lock this database so DO NOT FORGET THIS PASSWORD.

After creating the secure database click on "Add new entry" to enter and save your password and you should see something like shown below ... here you can also tell KeePassX to generate the secure password.

Save the changes to return back to the main screen and whenever you need to provide the username and password you can use the feature of "copy password to clipboard" or "copy username to clipboard" of KeePassX.

I hope this tutorial has been useful for you too! If you've enjoyed this post, please consider subscribing to Linuxpoison for future updates and more.

source:http://linuxpoison.blogspot.com/2009/06/135781757110287.html

tutorial - Hiding secret data into image and audio files (OpenSuSe)

Steghide is a steganography program that is able to hide data in various kinds of image and audio files. The color-frequencies (for image files) or sample-frequencies (for audio files) are not changed, thus making the embedding resistant against first-order statistical tests.

Features include:
    * Compression of embedded data
    * Encryption of embedded data
    * Embedding of a checksum to verify the integrity of the extraced data
    * Support for JPEG, BMP, WAV and AU files

Installation:
You should have the following packages (libraries) installed to use steghide. (you can get all these lib from software.opensuse.org) Mhash, MCrypt, libjpeg, zlib

Download the rpm file for Steghide
Install this rpm file using command: # rpm -ivh steghide-0.5.1-1.i386.rpm

The basic usage is as follows: Go to command prompt and use following commands

$ steghide embed -cf image.jpeg -ef file.txt
Enter passphrase:
Re-Enter passphrase:
embedding "file.txt" in "image.jpeg"... done

This command will embed the file file.txt in the cover file image.jpeg.

After you have embedded your secret data as shown above you can send the file image.jpeg to the person who should receive the secret message. The receiver has to use steghide in the following way:

$ teghide extract -sf image.jpeg
Enter passphrase:
the file "file.txt" does already exist. overwrite ? (y/n) y
wrote extracted data to "file.txt".

If the supplied passphrase is correct, the contents of the original file file.txt will be extracted from the stego file image.jpeg and saved in the current directory.

If you have received a file that contains embedded data and you want to get some information about it before extracting it, use the info command:

$ steghide info image.jpeg
"image.jpeg":
format: jpeg
capacity: 9.9 KB
Try to get information about embedded data ? (y/n) y
Enter passphrase:
embedded file "file.txt":
    size: 129.0 Byte
    encrypted: rijndael-128, cbc
    compressed: yes

source:http://linuxpoison.blogspot.com/2009/06/13578175719182.html

tutorial - Mac4lin - Give that Mac OS X look to Linux

Mac4Lin is best Mac like User Interface for Gnome and Xfce desktops like Ubuntu/Xubuntu, Fedora, Debian and others, that will take care of absolutely everything (from icons, themes to usplash – loading window at start) to look just like Mac. With this package comes: dock, the GTK theme, Emerald theme (3d window borders), new icons, new wallpapers, taskbar image, GDM themes, cursors, themes for Pidgin, Firefox, music players and system sounds and you will be amazed of flexibility and customization of Linux system.

Features:

    * Fully supports GNOME 2.26 and backwards compatible
    * Improved support for GlobalMenu, support integrated in the default GTK theme
    * Better native Xfce support
    * Icon additions
    * Statusbar is now fixed
    * New progress bars
    * New tabs
    * Improved installation and uninstallation scripts
    * Integrates well with Globus
    * Finer UI refinements
    * Metacity theme now supports different button sizes
    * Firefox 3 themes are now updated
    * Songbird plugins included
    * Pidgin AWN 64bit plugin now included
    * Fonts are now consolidated
    * Transparent top panel
    * GDM theme is now in-line with Mac OS X login window
    * Cairo dock is the default recommended dock

Issues:

* Usplash is still buggy
* Thunderbird theme is still buggy
* GDM theme is not automatically set by the script

Installation:

Download Mac4Lin file and extract the archive. Run the Mac4Lin installation script (./Mac4Lin_Install_v1.0.sh) as a normal user to install Mac4Lin.

If you'd like to manually install or apply some tweaks, check out the Mac4Lin documentation for advanced installation instructions.

Also, download entire sets of Mac Leopard Wallpapers

source:http://linuxpoison.blogspot.com/2009/06/135781757119583.html

tutorial - Query Apache logfiles via SQL

The Apache SQL Analyser (ASQL) is designed to read Apache log files and dynamically convert them to SQLite format so you can analyse them in a more meaningful way. Using the cut, uniq and wc commands, you can parse a log file by hand to figure out how many unique visitors came to your site, but using Apache SQL Analyser is much faster and means that the whole log gets parsed only once. Finding unique addresses is as simple as a SELECT DISTINCT command.

In terms of requirements you will need only the Perl modules for working with SQLite database, and the Term::Readline module. Upon a Debian system you may install both via:

apt-get install libdbd-sqlite3-perl libterm-readline-gnu-perl

Usage
Once installed, either via the package or via the source download, please start the shell by typing "asql". Once the shell starts you have several commands available to you, enter help for a complete list. The three most commonly used commands would be: load, select & show

The following sample session provides a demonstration of typical usage of the shell, it demonstrates the use of the alias command which may be used to create persistent aliases:

asql v0.6 - type 'help' for help.
asql> load /var/logs/apache/access.log
Loading: /var/logs/apache/access.log
sasql> select COUNT(id) FROM logs
46
asql> alias hits SELECT COUNT(id) FROM logs
ALIAS hits SELECT COUNT(id) FROM logs
asql> alias ips SELECT DISTINCT(source) FROM logs;
ALIAS ips SELECT DISTINCT(source) FROM logs;
asql> hits
46
asql> alias
ALIAS hits SELECT COUNT(id) FROM logs
ALIAS ips SELECT DISTINCT(source) FROM logs;

(User-input is in bold for emphasis)

source:http://linuxpoison.blogspot.com/2009/07/13578175711787.html

tutorial - Multi-protocol, Multi-source, Fast and Reliable Download Utility - aria2

aria2 is a multi-protocol & multi-source, cross platform download utility. The supported protocols are HTTP(S), FTP, BitTorrent (DHT, PEX, MSE/PE), and Metalink.

aria2 can download a file from multiple sources/protocols and tries to utilize your maximum download bandwidth. It supports downloading a file from HTTP(S)/FTP and BitTorrent at the same time, while the data downloaded from HTTP(S)/FTP is uploaded to the BitTorrent swarm. Using Metalink's chunk checksums, aria2 automatically validates chunks of data while downloading a file like BitTorrent.

There are other alternative applications. But aria2 has 2 distinctive features:

(1) aria2 can download a file from several URIs(HTTP(S)/FTP/BitTorrent)
(2) If you give aria2 a list of URIs, aria2 downloads them concurrently.

You don't have to wait for the current download queue to finish one file at a time anymore. aria2 tries to utilize your maximum download bandwidth and downloads files quickly.

Installation: aria2 binary packages are now available on the variety of platforms.
Debian & Ubuntu: apt-get install aria2
Fedora: yum install aria2
OpenSuse 11.1: "1-click" installer for aria2
Mandriva: urpmi aria2

Usage:
aria2 uses 5 connections to download 1 file by default. To limit the number of connections to, say, just 1, use -s1 option.

Note: To pause a download, press Ctrl-C. You can resume the transfer by running aria2c with the same arguments at the same directory. You can change URIs as long as they are pointing to the same file.

Download a file:

aria2c http://host/image.iso

Download a file using 2 connections:
aria2c -s2 http://host/image.iso http://mirror1/image.iso http://mirror2/image.iso

Download a file from HTTP and FTP servers:
aria2c http://host1/file.zip ftp://host2/file.zip

source:http://linuxpoison.blogspot.com/2009/07/135781757115795.html

tutorial - How do Flush DNS Cache in Linux

Most DNS clients cache the results of name resolution requests. This speeds up name resolution if multiple lookups are done to the same address, such as is common when browsing the web.

Sometimes a bad DNS entry will be cached and you will need to either flush the DNS cache to get rid of it, or wait up to 24 hours for it to be dropped from the cache automatically.

In Linux, the nscd daemon manages the DNS cache.
To flush the DNS cache, restart the nscd daemon using command: # /etc/init.d/nscd restart

source:http://linuxpoison.blogspot.com/2009/07/13578175712653.html

tutorial - Improving filesystem read performance using "noatime"

Linux records information about when files was last accessed. There is a cost associated with recording the last access time. The ext3 file system of Linux has an attribute that allows the super-user to mark individual filesystem to ignore recording of last access time. This may lead to significant performance improvements on often accessed frequently changing files such as the contents of the web server directory.

The only drawback is that none of the file's atime (access time) will be updated.

Linux has a special mount option for file systems called "noatime" that can be added to each line that addresses one file system in the /etc/fstab file. If a file system has been mounted with this option, reading accesses to the file system will no longer result in an update to the atime (access time) information associated with the file.

The importance of the noatime setting is that it eliminates the need by the system to make writes to the file system for files which are simply being read. Since writes can be somewhat expensive, this can result in measurable performance gains.

Note that the write time information to a file will continue to be updated anytime the file is written to.

Edit the fstab file vi /etc/fstab and add in the line that you are interested in adding the "noatime" option show below:

/dev/sda1 /var/www ext3 defaults,noatime 1 2

source:http://linuxpoison.blogspot.com/2009/07/13578175713274.html

tutorial - Auto reboot after kernel panic

When a kernel encounters certain errors it calls the "panic" function which results from a unrecoverable error. This panic results in LKCD (Linux Kernel Crash Dump) initiating a kernel dump where kernel memory is copied out to the pre-designated dump area. The dump device is configured as primary swap by default. The kernel is not completely functional at this point, but there is enough functionality to copy memory to disk. When the system boots back up, it checks for a new crash dump. If a new crash dump is found it is copied from the dump location to the file system, "/var/log/dump" directory by default. After copying the image, the system continues to boot normally and forensics can be performed at a later date.

By default after a kernel panic, system just waits there for a restart. This is because of the value set on "kernel.panic" parameter.

# cat /proc/sys/kernel/panic
0

To disable this and make the Linux OS reboot after a kernel panic, we have to set an integer value greater than zero to the paramter "kernel.panic", where the value is the number of seconds to wait before a automatic reboot. For example , if you set it to "10" , then the system waits for 10 seconds before automatic reboot. To make this permanent, edit /etc/sysctl.conf and add following like at end of the file.

kernel.panic = 10

source:http://linuxpoison.blogspot.com/2009/07/135781757110396.html

tutorial - Limit the CPU usage of an application (process) - cpulimit

cpulimit is a simple program that attempts to limit the cpu usage of a process (expressed in percentage, not in cpu time). This is useful to control batch jobs, when you don't want them to eat too much cpu. It does not act on the nice value or other scheduling priority stuff, but on the real cpu usage. Also, it is able to adapt itself to the overall system load, dynamically and quickly.

Installation:
Download last stable version of cpulimit
Then extract the source and compile with make:

    tar zxf cpulimit-xxx.tar.gz
    cd cpulimit-xxx
    make

Executable file name is cpulimit. You may want to copy it in /usr/bin.

Usage:
Limit the process 'bigloop' by executable name to 40% CPU:

    cpulimit --exe bigloop --limit 40
    cpulimit --exe /usr/local/bin/bigloop --limit 40

Limit a process by PID to 55% CPU:

    cpulimit --pid 2960 --limit 55

cpulimit should run at least with the same user running the controlled process. But it is much better if you run cpulimit as root, in order to have a higher priority and a more precise control.

Note:
If your machine has one processor you can limit the percentage from 0% to 100%, which means that if you set for example 50%, your process cannot use more than 500 ms of cpu time for each second. But if your machine has four processors, percentage may vary from 0% to 400%, so setting the limit to 200% means to use no more than half of the available power. In any case, the percentage is the same of what you see when you run top.

source:http://linuxpoison.blogspot.com/2009/07/135781757118417.html

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