Tutorial Proggraming Free

tutorial - How to set limits on users

The ulimit programs allow to limit system-wide resource use using a normal configuration file - /etc/security/limits.com. This can help a lot in system administration, e.g. when a user starts too many processes and therefore makes the system unresponsive for other users.

$ ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 7671
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) 811664
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 7671
virtual memory          (kbytes, -v) 1175120
file locks                      (-x) unlimited

All these settings can be manipulated. A good example is this forkbomb that forks as many processes as possible and can crash systems where no user limits are set - see this example - here

Warning: Do not run this program! If no limits are set your system will either become unresponsive or might even crash.

Now this is not good - any user with shell access to your box could take it down. But if that user can only start 20 processes the damage will be minimal. So let's set a process limit of MAX 20 process for a particular users in the system, this can be done by inserting the simple one line in limit.conf file.

Following will prevent a "fork bomb":

nikesh hard nproc 20
@group1 hard nproc 50

Above will prevent user "nikesh" to create more than 20 process and anyone in the group1 from having more than 50 processes.

There are many more setting and limits that you can set on a particular user or to a entire group like ..

using below configuration will prevent any users in the system to logins not more than 3 places at same time.
* hard maxlogins 3

Limit on size of core file
* hard core 0

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source:http://linuxpoison.blogspot.com/2009/01/13578175713117.html

tutorial - Linux terminal server (RDP) on OpenSuse 11.1

Based on the work of rdesktop, xrdp uses the remote desktop protocol to present a GUI to the user.

The goal of this project is to provide a fully functional Linux terminal server, capable of accepting connections from rdesktop and Microsoft's own terminal server/remote desktop clients.

Unlike Windows NT/2000/2003/2008 server, xrdp will not display a Windows desktop but an X window desktop to the user. Xrdp uses Xvnc or X11rdp to manage the X session.

Installation and Configuration:
Go to YAST -- Software management and search for "xrdp" you should able to find it under OpenSuse 11.1 OSS repository

Click on "Accept" to install the xrdp pacakage.

2) After sucessfull installation start the xrdp server (terminal server) using following command

sudo /usr/sbin/service xrdp start
or
rcxrdp start (as root)

If you have your firewall turned on be sure you allow the port: Tcp 3389

3) Now finally use your rdp client (from windows box) and try to connect to this linux terminal server (Xrdp), you should be see something like ...

source:http://linuxpoison.blogspot.com/2009/01/135781757117683.html

tutorial - How to restrict features of the KDE desktop for users on OpenSuse 11.x

KIOSK Admin Tool is a KDE administration tool that offers system administrators an easy way to predefine desktop configurations for groups of users, lock down settings or otherwise restrict features of the KDE desktop environment.

KIOSK Admin Tool takes advantage of KDE's KIOSK restrictions framework. It is centered around profiles. A profile is a collection of default settings and restrictions that can be applied to either individual users or groups of users.

Typical usage of KIOSK Admin Tool is to create a new profile, then to set up the profile with the desired default settings and restrictions, and finally to activate the profile by assigning the profile to one or more users or to a group of users.

1) Open the terminal and fire command : # kiosktool to open the main KIOSK admin window

2) Now you can create a new profile, after creation click on "Set up profile" to do the actual restriction on the desktop

Here you can lock down components in a dozen categories: General, Desktop Icons, Desktop Background, Screen Saver, KDE Menu, Theming, Panel, Network Proxy, Konqueror, Menu Actions, Desktop Sharing, and File Associations.

The General component provides useful options like disabling all tasks and applications that require root access, as well as access to the command shell, run command, bookmarks, and logout option, and disabling starting a second X session.

Desktop Icons lets you lock down the whole desktop for the user, including context menus and icons. Desktop Background locks the desktop background settings. With Screen Saver, sysadmins can lock down screensaver settings and screensavers that uses OpenGL, and also allow only screensavers that hide the whole screen content.

In the KDE Menu component you can disable all tasks and applications that require root access from the KDE menu, and disable editing the KDE menu. The Theming component forces users to stick with the desktop theme you provide; you can lock down options like font, color, style, and windows decoration.

finally save the setting..

3) After sucessfull configuration, assign the profle to a user or to a group

[Ref: http://www.linux.com/feature/114306]

source:http://linuxpoison.blogspot.com/2009/01/13578175713497.html

tutorial - Using vi to Encrypt Text Files

The disadvantage of using encrypted partitions is that while the partition is mounted, at least root can access the data. To prevent this, vi can be used in encrypted mode.

Use vi -x filename to edit a new file. vi prompts you to set a password, after which it encrypts the content of the file. Whenever you access this file, vi requests the correct password.

For even more security, you can place the encrypted text file in an encrypted partition. This is recommended because the encryption used in vi is not very strong.

source:http://linuxpoison.blogspot.com/2009/01/13578175718959.html

tutorial - Advantages of IPv6 - The Next Generation Internet

The most important and most visible improvement brought by the new protocol is the enormous expansion of the available address space. An IPv6 address is made up of 128 bit values instead of the traditional 32 bits. This provides for as many as several quadrillion IP addresses.

However, IPv6 addresses are not only different from their predecessors with regard to their length. They also have a different internal structure that may contain more specific information about the systems and the networks to which they belong.

The following is a list of some other advantages of the new protocol:

Autoconfiguration
IPv6 makes the network “plug and play” capable, which means that a newly set up system integrates into the (local) network without any manual configuration. The new host uses its automatic configuration mechanism to derive its own address from the information made available by the neighboring routers, relying on a protocol called the neighbor discovery (ND) protocol. This method does not require any intervention on the administrator's part and there is no need to maintain a central server for address allocation—an additional advantage over IPv4, where automatic address allocation requires a DHCP server.

Mobility
IPv6 makes it possible to assign several addresses to one network interface at the same time. This allows users to access several networks easily, something that could be compared with the international roaming services offered by mobile phone companies: when you take your mobile phone abroad, the phone automatically logs in to a foreign service as soon as it enters the corresponding area, so you can be reached under the same number everywhere and are able to place an outgoing call just like in your home area.

Secure Communication
With IPv4, network security is an add-on function. IPv6 includes IPsec as one of its core features, allowing systems to communicate over a secure tunnel to avoid eavesdropping by outsiders on the Internet.

Backward Compatibility
Realistically, it would be impossible to switch the entire Internet from IPv4 to IPv6 at one time. Therefore, it is crucial that both protocols are able to coexist not only on the Internet, but also on one system. This is ensured by compatible addresses (IPv4 addresses can easily be translated into IPv6 addresses) and through the use of a number of tunnels. Also, systems can rely on a dual stack IP technique to support both protocols at the same time, meaning that they have two network stacks that are completely separate, such that there is no interference between the two protocol versions.

Custom Tailored Services through Multicasting
With IPv4, some services, such as SMB, need to broadcast their packets to all hosts in the local network. IPv6 allows a much more fine-grained approach by enabling servers to address hosts through multicasting—by addressing a number of hosts as parts of a group (which is different from addressing all hosts through broadcasting or each host individually through unicasting). Which hosts are addressed as a group may depend on the concrete application. There are some predefined groups to address all name servers (the all name servers multicast group), for example, or all routers (the all routers multicast group).

Configuring IPv6 on OpenSuse 11.1
To disable or enable IPv6 on an installed system, use the YaST Network Settings module. On the Global Options tab, check or uncheck the Enable IPv6 option as necessary. To enable IPv6 manually, enter modprobe ipv6 as root.

source:http://linuxpoison.blogspot.com/2009/01/13578175714416.html

tutorial - Enigma Desktop for Linux

This sexy desktop mod was initially designed for windows but it's now ported to Linux. Give it a try.

Download Enigma Desktop & Get Installation Instructions.

source:http://linuxpoison.blogspot.com/2009/01/13578175715443.html

tutorial - Best GDM Theme - Think Of Penguins

This is one of the best GDM theme I ever seen

Download it from here

source:http://linuxpoison.blogspot.com/2009/01/135781757113584.html

tutorial - Encrypt-Decrypt files using mcrypt on OpenSuse

MCrypt is a replacement for the old crypt() package and crypt(1) command, with extensions. It allows developers to use a wide range of encryption functions, without making drastic changes to their code. It allows users to encrypt files or data streams without having to be cryptographers. Above all, it allows you to have some really neat code on your machine. :)

The companion to MCrypt is Libmcrypt, which contains the actual encryption functions themselves, and provides a standardized mechanism for accessing them.

Installation:
Go to Yast -- Software Management and search for "mycrypt" and select the pacakage and install it using yast

Examples of mcrypt usage in a linux command line environment:

See available encryption algorithms
mcrypt --list

Encrypts myfilename to myfilename.nc using blowfish encryption algorithm, you are prompted 2x for passphrase
mcrypt -a blowfish myfilename

Decrypts mytextfile.txt.nc to mytextfile.txt
mcrypt -d mytextfile.txt.nc

For Other options
mcrypt --help

It implements numerous cryptographic algorithms, mostly block ciphers and stream ciphers, some of which falls under export restrictions in the United States. Algorithms include des, blowfish, arcfour, enigma, ghost, loki97, rc2, serpent, threeway, twofish, wake, xtea

source:http://linuxpoison.blogspot.com/2009/01/13578175712575.html

tutorial - E-Mail Notification for OpenSuse 11.x

Mail Notification monitors your mailboxes for new mail.

When new mail arrives, Mail Notification alerts you by displaying an icon in the notification area. Moreover, a mail summary can be displayed in the icon tooltip, a sound can be played, and notifications containing useful action buttons can be popped up.

Mail Notification can monitor multiple mailboxes concurrently, and supports Evolution, Gmail, IMAP, Maildir, mbox, MH, Mozilla products (Mozilla, SeaMonkey, Thunderbird, …), POP3, Sylpheed, Windows Live Hotmail and Yahoo! Mail mailboxes.

Mail Notification supports advanced POP3 and IMAP features such as SSL/TLS connections (in-band or on separate port), SASL and APOP authentication, and the IMAP IDLE extension.

Installation:

Go to yast -- Software management and search for "mail-notification", after finding the package you can directly install it

After successful installation, you can find the "mail-notification" software under "Internet" -- "E-Mail" program list,

The interface is simple, functional, respects the GNOME Human Interface Guidelines and integrates well into the GNOME Desktop Environment (though Mail Notification can also be used with KDE, Xfce and other environments).

After sucessfull configuration of you inbox you should see something like .. on receiving new mail

source:http://linuxpoison.blogspot.com/2009/01/13578175717280.html

tutorial - How to Enable-Disable Novell AppArmor on OpenSuse 11.1

Novell AppArmor is configured to run by default on any fresh installation of openSUSE. There are two ways of toggling the status of AppArmor:

Using YaST System Services (Runlevel)
Disable or enable AppArmor by removing or adding its boot script to the sequence of scripts executed on system boot. Status changes are applied at the next system boot.

   1.Start YaST.
   2.Select System+System Services (Runlevel).
   3.Select Expert Mode.
   4.Select boot.apparmor and click Set/Reset+Disable the service.
   5.Exit the YaST Runlevel tool with Finish.

AppArmor will not be initialized on the next system boot and stays inactive until you explicitly reenable it

To toggle AppArmor's status by using AppArmor Control Panel

   1.Start YaST.
   2.Select Novell AppArmor+AppArmor Control Panel.
   3.Select Enable AppArmor. To disable AppArmor, uncheck this option.
   4.Exit the AppArmor Control Panel with Done.

source:http://linuxpoison.blogspot.com/2009/01/13578175712506.html

tutorial - Network Monitoring and Management Tool

AutoScan-Network is a network discovering and managing application. No configuration is required to scan your network. The main goal is to print the list of connected equipments in your network.

Features:
•Multithreaded Scan
•Automatic network discovery
•Low surcharge on the network
•Simultaneous subnetworks scans without human intervention
•Realtime detection of any connected equipment
•Supervision of any equipment (router, server, firewall...)
•Supervision of any network service (smtp, http, pop, ...)
•Automatic detection of known operatic system (brand and version), you can also add any unknown equipment to the database
•Complete network tree can be saved in a XML file.
•Intruders detection (in intruders detection mode, all new equipments blacklisted)
•Telnet Client
•Nessus Client
•Wake on lan functionality
•Privileged account is not required

Installation:
To install AutoScan-Network, go on this link http://autoscan-network.com/ and download the latest version for your operating system.

Once you've downloaded the package, decompress the 'tar.gz' file and double-click on the binary file "AutoScan-Network-Linux-1.1x.bin" The installation starts...

(If you get troubles during the installation, start a shell with root access privileges and re-execute the binary file) This is the simplest way to install AutoScan-Network but some features are not included (like file sharing support) after successful installation you should find the entry of the application in your KDE start menu, start the application and you should see something like ..

To un-install AutoScan-Network start a shell with root access privileges, and type '/opt/AutoScan/uninstall'

AutoScan Network is free software. It is licensed under the GNU General Public License (GPL) version 2. This means you are free to use it and to modify it.

source:http://linuxpoison.blogspot.com/2009/01/13578175716321.html

tutorial - FTP, FTPS and SFTP client - BareFTP

bareFTP is a file transfer client supporting the FTP, FTP over SSL/TLS (FTPS) and SSH File Transfer Protocol (SFTP). It is written in C#, targeting the Mono framework and the GNOME desktop environment. bareFTP is free and open source software released under the terms of the GPL license.

Installation - Binary packages:

	Ubuntu 8.10 (intrepid): bareftp_0.1.4-1_i386.deb (mirror)
	Fedora 10: bareftp-0.1.4-4.i386.rpm (mirror) bareftp-0.1.4-4.x86_64.rpm (mirror)
	openSUSE: openSUSE 11.1 bareftp-0.1.4-4.i586.rpm (mirror) openSUSE 11.0 bareftp-0.1.4-4.i586.rpm (mirror) You can also subscribe to the PackMan repository (with a small delay on new releases)

Dependencies:
You'll need this to run bareFTP:
    * Mono >= 2.0
    * Gtk# >= 2.12 (gtk-sharp2)
    * Gnome# >= 2.20 (gnome-sharp)

OpenSuse user can go to yast -- software management and search for "bareFTP" and and can install it from yast.

On sucessfull installation you can find the "bareFTP" under "Application -- Internet -- data exchange" menu

source:http://linuxpoison.blogspot.com/2009/01/1357817571573.html

tutorial - KDE 4.2 installation/upgrade on Debian,Kbuntu and OpenSuse

January 27, 2009. The KDE Community announced the immediate availability of "The Answer", (a.k.a KDE 4.2.0), readying the Free Desktop for end users. KDE 4.2 builds on the technology introduced with KDE 4.0 in January 2008. After the release of KDE 4.1, which was aimed at casual users, the KDE Community is now confident we have a compelling offering for the majority of end users.

Debian
KDE 4.2.0 packages are in the experimental repository. Installation Information .

Kubuntu
Januty: Packages for the development Jaunty release are available. If you use Jaunty you will be able to upgrade as normal.

Interpid:
Packages for Kubuntu 8.10 can be installed by following the instructions below. If you installed KDE 4.2 Beta or RC you can merely update your existing installation.

Instructions
The updated packages for Kubuntu 8.10 are located in the Kubuntu Experimental Software Personal Package Archive (PPA) repository. To update to KDE 4.2, please follow these instructions:

1) Remove the koffice-data-kde4 package if you have it installed. The current koffice2 packages in the kubuntu-members-kde4 PPA are incompatible with the KDE 4.2 packages since they try to install icons to the same locations.

2)Follow the Kubuntu Repository Guide to enable Recommended Updates and add the following to your 'Third-Party Software' tab:

deb http://ppa.launchpad.net/kubuntu-experimental/ubuntu intrepid main

3) You can add the package signing key with this command:

gpg --keyserver keyserver.ubuntu.com --recv-keys 493B3065 && gpg --export -a 493B3065 | sudo apt-key add -

4) Old Plasma packages are not compatible with KDE 4.2, you should uninstall any plasmoids.

5) You can now update any existing KDE 4 installation to the most recent version using the Adept Updater tool in your system tray.

6) Now log out and press Alt + E to restart X. When you log in you will have KDE 4.2.

Opensuse
openSUSE packages are available in one click installation for
openSUSE 11.1 (one-click install )
openSUSE 11.0 (one-click install )
openSUSE 10.3 (one-click install ).
KDE Four Live CD with KDE 4.2 is also available .

Compiling KDE 4.2.0
The complete source code for KDE 4.2.0 may be freely downloaded . Instructions on compiling and installing KDE 4.2.0 are available from the KDE 4.2.0 Info Page .

Spread the Word
The KDE team encourages everybody to spread the word on the Social Web as well. Submit stories to websites, use channels like delicious, digg, reddit, twitter, identi.ca. Upload screenshots to services like Facebook, FlickR, ipernity and Picasa and post them to appropriate groups. Create screencast, upload them to YouTube, Blip.tv, Vimeo and others. Do not forget to tag uploaded material with the tag kde42 so it is easier for everybody to find the material, and for the KDE team to compile reports of coverage for the KDE 4.2 announcement. This is the first time the KDE team is attempting a coordinated effort to use social media for their messaging. Help KDE spreading the word, be part of it.

On web forums, inform people about KDE's new compelling features, help others getting started with their new desktop.

Reporting KDE Bugs
Please report all KDE bugs and feature requests at bugs.kde.org . The site has a nice bug-reporting "wizard" and will permit far easier tracking of bugs than an email to a list.

Sources
kde.org
Kubuntu

source:http://linuxpoison.blogspot.com/2009/01/135781757119589.html

tutorial - Advanced shutdown utility for OpenSuse 11.1

GShutdown is a utility that allows you to schedule shutdown, logout, and reboot for your computer. It is compatible with GNOME, KDE, and XFCE. In KDM and GDM, you can shutdown or reboot your computer without the need to be root. You can choose a command to stop the computer (like "sudo poweroff"). It has a systray icon with visual notifications. There are 3 different ways to schedule the action: at a time and date, after a delay, or now. There are command line options to change the default values.

OpenSuse 11.1 user can use "1-click" installer - here or if you already subcribe to packman, go to yast -- software management and search for "gshutdown" (shown below)

After successful installation, go to terminal and fire the command # gshutdown and you should see something like ..

There are lot of other option that you can configure for shutdown.

source:http://linuxpoison.blogspot.com/2009/02/135781757112811.html

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