Tutorial Proggraming Free

tutorial - How to Configure Apache as a Forward / Reverse Proxy

Apache can be configured in both a forward and reverse proxy (also known as gateway) mode.

Apache as Forward Proxy:
An ordinary forward proxy is an intermediate server that sits between the client and the origin server. In order to get content from the origin server, the client sends a request to the proxy naming the origin server as the target and the proxy then requests the content from the origin server and returns it to the client. The client must be specially configured to use the forward proxy to access other sites.

A typical usage of a forward proxy is to provide Internet access to internal clients that are otherwise restricted by a firewall. The forward proxy can also use caching (mod_cache) to reduce network usage.

The forward proxy is activated using the ProxyRequests directive. Because forward proxies allow clients to access arbitrary sites through your server and to hide their true origin, it is essential that you secure your server so that only authorized clients can access the proxy before activating a forward proxy.

ProxyRequests On
ProxyVia On

<Proxy *>
Order deny,allow
Deny from all
Allow from 192.168.1
</Proxy>

Apache as Reverse Proxy:
A reverse proxy (or gateway), by contrast, appears to the client just like an ordinary web server. No special configuration on the client is necessary. The client makes ordinary requests for content the reverse proxy then decides where to send those requests, and returns the content as if it was itself the origin.

A typical usage of a reverse proxy is to provide Internet users access to a server that is behind a firewall. Reverse proxies can also be used to balance load among several back-end servers, or to provide caching for a slower back-end server. In addition, reverse proxies can be used simply to bring several servers into the same URL space.

A reverse proxy is activated using the ProxyPass directive or the flag to the RewriteRule directive. It is not necessary to turn ProxyRequests on in order to configure a reverse proxy.

ProxyRequests Off

<Proxy *>
Order deny,allow
Allow from all
</Proxy>

ProxyPass /foo http://foo.example.com/bar
ProxyPassReverse /foo http://foo.example.com/bar

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source:http://linuxpoison.blogspot.com/2010/01/13578175715104.html

tutorial - MySQLTuner - Performance Tunning MySQL on Linux

MySQLTuner is a script written in Perl that allows you to review a MySQL installation quickly and make adjustments to increase performance and stability. The current configuration variables and status data is retrieved and presented in a brief format along with some basic performance suggestions.

*WARNING*
It is extremely important for you to fully understand each change you make to a MySQL database server. If you don't understand portions of the script's output, or if you don't understand the recommendations, you should consult a knowledgeable DBA or even a system administrator that you trust. Always test your changes on staging environments, and always keep in mind that improvements in one area can negatively affect MySQL in other areas.

Running MySQLTuner:
Download MySQLTuner using the following command

# wget http://mysqltuner.com/mysqltuner.pl

To run the script, simply make it executable and run it:

# chmod +x mysqltuner.pl
# ./mysqltuner.pl

Enter your administrative username and password
Output you can see as follows

source:http://linuxpoison.blogspot.com/2010/01/135781757117245.html

tutorial - Measuring the Performance of HTTP Web Servers using ApacheBench (ab)

ApacheBench is a command line utility for measuring the performance of HTTP web servers, in particular the Apache HTTP Server. It was designed to give an idea of the performance that a given Apache installation can provide. In particular, it shows how many requests per second the server is capable of serving.

The ab tool comes bundled with the standard Apache source distribution, and like the Apache web server itself, is free, open source software and distributed under the terms of the Apache.

Using ApacheBench (ab):
Suppose we want to see how fast Yahoo can handle 100 requests, with a maximum of 10 requests running concurrently:

ab -n 100 -c 10 http://www.yahoo.com/

As you can see this is very useful information, it returned requests at a rate of 16.50 requests per second, the fastest request was 556ms, the slowest 830ms.

Suppose you wanted to test multiple url's concurrently as well? You can do this by creating a shell script, with multiple ab calls. At the end of each line place an & this makes the command run in the background, and lets the next command start execution. You will also want to redirect the output to a file for each url using > filename For example:

#!/bin/sh

ab -n 100 -c 10 http://www.test.com/test1.html > test1.txt &
ab -n 100 -c 10 http://www.test2.com/test2.html > test2.txt &

source:http://linuxpoison.blogspot.com/2010/01/135781757116092.html

tutorial - How to Synchronize System Clock with NTP Time Server on OpenSuSe Linux

Networked computers share resources such as files. These shared resources often have time-stamps associated with them so it is important that computers communicating over networks, including the Internet, are synchronized. Imagine the confusion that could be created if an email appeared to arrive before being sent, or if an important file, modified in offices in different countries, had a version with a time-stamp indicating it had been created two hours later than its updated version.

The Network Time Protocol (NTP) is an Internet Standard Recommended Protocol for communicating the Coordinated Universal Time (UTC) from special servers called time servers and synchronizing computer clocks on an IP network.

Time Servers, or time source references, communicate with special time keeping equipment such as Global Positioning System (GPS) receivers, atomic clocks, radios, satellite receivers or modems.

The accuracy of each time server is defined by a number called its stratum. Stratum one servers are those at the top level which communicate directly with a time source such as a GPS or an atomic clock. Each level downwards in the hierarchy is classified as one greater than the preceding level (for example, stratum two, stratum three). Current stratum one servers can provide time within a millisecond's accuracy or better.

For a list of available Stratum 1 and 2 servers consult http://www.ntp.org/
You can get the list of the NTP server based on your region (country) - http://www.pool.ntp.org/en/

Installation:
OpenSuSe user can install NTP using "1-click" installer - here

Configuring NTP
The ntp.conf' file is main source of configuration information for a NTP server installation. Amongst other things, it contains a list of reference clocks that the installation is to synchronise. A list of NTP server references is specified with the server' configuration command thus or the same thing can be configure using YAST control center:

Go to Yast → System → Date and Time, click on "Change" button to open up the NTP configuration dialog box.

Provide the name of the appropriate time server located in your region (country) and click on "Accept" save the confguration in your ntp.conf'

Now, start your ntp daemon (/etc/init.d/ntp start) to make sure that your system clock keep getting synchronized with the specified time server.

source:http://linuxpoison.blogspot.com/2010/01/135781757117925.html

tutorial - shred - Securely delete files in Linux

In case you want to delete some confidential data from your computer just to make sure that it is no longer accessible to anyone, then do not delete the file using the regular rm command because there will still remain a chance that someone might use a software to recover your deleted data before the specific storage area is overwritten by new data. The proper way to permanently dispose of such data in Linux is the shred command.

* NOTE *

In the case of ext3/ext4 file systems, in both the data=ordered (default) and data=writeback modes, shred works as usual.Ext3/Ext4 journaling modes can be changed by adding the data=something option to the mount options for a particular file system in the /etc/fstab file.

Most Linux distribution come with shred already installed. If not, they are one click away in the repositories. shred is already included, in the multipurpose package called coreutils, which includes tens of utilities.

Using shred:
shred is a command utility. It can be run against files or folders, with certain flags.

# shred -f -u -v -z filename

-f change permissions to allow writing if necessary
-u truncate and remove file after overwriting
-v be verbose (detailed) and show progress
-z add a final overwrite with zeros to hide shredding

shred might not work on bad sectors, it is one of the best tools available to securely erase data from your hard disk. It is always more secure to run shred on a complete partition rather than a file, because some filesystems keep backup files and shred makes no attempt to delete these.

# shred /dev/hda2

source:http://linuxpoison.blogspot.com/2010/01/13578175719453.html

tutorial - pngcrush - Optimize PNG file (image) to Speed up WebSite

Pngcrush is an excellent batch-mode compression utility for PNG images. Depending on the application that created the original PNGs, it can improve the file size anywhere from a few percent to 40% or more (completely losslessly). The utility also allows specified PNG chunks (e.g. text comments) to be inserted or deleted, and it can fix incorrect gamma info.

Pngcrush is not installed by default in Linux, but it is available in the repositories of most Linux distributions. In Ubuntu Linux, you can install pngcrush by running the following command :

$ sudo apt-get install pngcrush

OpenSuSe user can install Pngcrush using "1-click" installer - here

Using pngcrush
Running the Pngcrush command with no options may produce smaller files. Here is how we can use it to optimize and reduce size of PNG files -

$ pngcrush -brute -e "Optimize.png" filename.png

-brute – Use brute force, try 114 different filter/compression methods. This option is very time consuming but will able to reduce the size of PNG images by significant factor using this option.

-e "ext" – Specify a new extension for all output files. In the above example, the output of the command will be a file named filename Optimize.png . You can use any extension you want. This option ensures that the original file is not overwritten.

More examples
$ pngcrush -brute -d "/home/laf/images/pngcrush/" *.png

All the files in the current directory are optimized and saved in the directory denoted by the -d option.

source:http://linuxpoison.blogspot.com/2010/01/1357817571783.html

tutorial - Etherape - A Graphical Network Monitor for Linux

EtherApe is a graphical network monitor for Unix modeled after etherman. Featuring link layer, ip and TCP modes, it displays network activity graphically. Hosts and links change in size with traffic. Color coded protocols display.

EtherApe supports Ethernet, FDDI, Token Ring, ISDN, PPP and SLIP devices. It can filter traffic to be shown, and can read traffic from a file as well as live from the network.

EtherApe Feature:

Network traffic is displayed graphically. The more "talkative" a node is, the bigger its representation.
Node and link color shows the most used protocol.
User may select what level of the protocol stack to concentrate on.
You may either look at traffic within your network, end to end IP, or even port to port TCP.
Data can be captured "off the wire" from a live network connection, or read from a tcpdump capture file.
Live data can be read from ethernet, FDDI, PPP, SLIP and WLAN interfaces, plus several other encapsulated formats (e.g. Linux cooked, PPI).
The following frame and packet types are currently supported: ETH_II, 802.2, 803.3, IP, IPv6, ARP, X25L3, REVARP, ATALK, AARP, IPX, VINES, TRAIN, LOOP, VLAN, ICMP, IGMP, GGP, IPIP, TCP, EGP, PUP, UDP, IDP, TP, ROUTING, RSVP, GRE, ESP, AH, EON, VINES, EIGRP, OSPF, ENCAP, PIM, IPCOMP, VRRP; and most TCP and UDP services, like TELNET, FTP, HTTP, POP3, NNTP, NETBIOS, IRC, DOMAIN, SNMP, etc.
Data display can be refined using a network filter using pcap syntax.
Display averaging and node persistence times are fully configurable.
Name resolution is done using standard libc functions, thus supporting DNS, hosts file, etc.
Clicking on a node/link opens a detail dialog showing protocol breakdown and other traffic statistics.
Protocol summary dialog shows global traffic statistics by protocol.
Node summary dialog shows traffic statistics by node.
Scrollkeeper/rarian-compatible manual integrated with yelp.

EtherApe Installation:
OpenSuSe user can install EtherApe using "1-click" installer - here
Ubuntu user can install EtherApe using command: sudo aptitude install etherape

After successful installation, go to terminal and type command : etherape
When you fire up EtherApe, you see a dynamic Web of traffic (shown below in picture)

source:http://linuxpoison.blogspot.com/2010/01/13578175713709.html

tutorial - How to set MTU (Maximum Transmission Unit) value on OpenSuSe Linux

In computer networking, the maximum transmission unit (MTU) of a layer of a communications protocol is the size (in bytes) of the largest protocol data unit that the layer can pass onwards.

MTU parameters usually appear in association with a communications interface (NIC, serial port, etc.). Standards (Ethernet, for example) can fix the size of an MTU; or systems (such as point-to-point serial links) may decide MTU at connect time. A higher MTU brings greater efficiency because:

each packet carries more user-data
protocol overheads, such as headers or underlying per-packet delays, remain fixed,
higher efficiency means a slight improvement in bulk protocol throughput

For sending bulk data, the Internet generally works better when using larger packets. Each packet implies a routing decision, when sending a 1 megabyte file, this can either mean around 700 packets when using packets that are as large as possible, or 4000 if using the smallest default.

However, not all parts of the Internet support full 1460 bytes of payload per packet. It is therefore necessary to try and find the largest packet that will 'fit', in order to optimize a connection.

This process is called 'Path MTU Discovery', where MTU stands for 'Maximum Transfer Unit.'

Setting MTU value in OpenSuSe Linux:
Go to Yast → Network Device → Network Settings
In Network Setting dialog dialog box, select "Overview" tab and click on "Edit" button, this will open up your Network card setting dialog box, click on "General" tab to set the MTU for this card as shown in the figure below

To view the updated MTU, type command: ip link list you should see the output similar to ...

1: lo: mtu 16436 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
link/ether 00:19:d1:18:ba:a6 brd ff:ff:ff:ff:ff:ff

source:http://linuxpoison.blogspot.com/2010/01/135781757115264.html

tutorial - How to Disable ICMP Redirects in Linux

ICMP redirect messages represent one of the lowest level routing protocols for simple redirects. Routers send them to hosts to inform them about more efficient ways to reach a host rather than route them over themselves. A host will allow this message and will store this "hint" in a temporary table. It will send the next package directly to the host given by the ICMP redirect.

However, the Linux kernel doesn't listen to ICMP redirects when it is configured as router and not as host. So, be careful setting up routing tables for routers. They have to be complete. No hints from other hosts will be accepted and only the local routing table decides where packages go.

Disable ICMP Redirects:
In most of the Linux flavors (Debian, Ubuntu, Redhat Enterprise linux, OpenSuSe) ICMP Redirects can be dynamically disabled on the host by adding the proper entries in the /etc/sysctl.conf configuration file. Simply edit the /etc/sysctl.conf file and add the following entries:

For IPv4

net.ipv4.conf.all.accept_redirects = 1
net.ipv4.conf.all.send_redirects = 1

For Ipv6

net.ipv6.conf.all.accept_redirects = 1
net.ipv6.conf.all.send_redirects = 1

source:http://linuxpoison.blogspot.com/2010/01/13578175718969.html

tutorial - Ratproxy - A Passive Web Application Security Assessment Tool

Ratproxy is a semi-automated, largely passive web application security audit tool, optimized for an accurate and sensitive detection, and automatic annotation, of potential problems and security-relevant design patterns based on the observation of existing, user-initiated traffic in complex web 2.0 environments.

Ratproxy also detects and prioritizes broad classes of security problems, such as dynamic cross-site trust model considerations, script inclusion issues, content serving problems, insufficient XSRF and XSS defenses, and much more.

Ratproxy is a local program designed to sit between your Web browser and the application you want to test. It logs outgoing requests and responses from the application, and can generate its own modified transactions to determine how an application responds to common attacks.

    The list of low-level tests it runs is extensive, and includes:
    potentially unsafe JSON-like responses
    bad caching headers on sensitive content
    suspicious cross-domain trust relationships
    queries with insufficient XSRF defenses
    suspected or confirmed XSS and data injection vectors

Installation:
OpenSuSe user can install Ratproxy using "1-click" installer - here

Running Ratproxy:

# ratproxy -v /tmp/ -w ratlog.txt -d hell.com -lfscm
ratproxy version 1.58-beta by
[*] Proxy configured successfully. Have fun, and please do not be evil.
[+] Accepting connections on port 8080/tcp (local only)...

-d parameter tells ratproxy to run tests only on URLs at the specified domain, so it won't accidentally test a site your application links to for images or advertising.
-v parameter tells it where to write trace files.
-w parameter indicates where log records should be written.

Once the proxy is running, you need to configure your web browser to point to the appropriate machine and port (8080) it is advisable to close any non-essential browser windows and purge browser cache, as to maximize coverage and minimize noise.

The next step is to open the tested service in your browser, log in if necessary, then interact with it in a regular, reasonably exhaustive manner: try all available views, features, upload and download files, add and delete data, and so forth - then log out gracefully and terminate ratproxy with Ctrl-C.

Generating Ratproxy Report:

Once the proxy is terminated, you may further process its pipe-delimited (|), machine-readable, greppable output with third party tools if so desired, then generate a human-readable HTML report:

# ratproxy-report.sh ratproxy.log >report.html

This will produce an annotated, prioritized report with all the identified issues.

source:http://linuxpoison.blogspot.com/2010/01/1357817571480.html

tutorial - HowTo Find out if Installed Linux is 32 bits or 64 bits

To figure out whether we have installed Linux is of 32 bits or 64 bits, you can run the following command in a Terminal:

uname -m

The possible outcomes and their meanings are:

* i686 : Installed 32-bit version.
* x86_64 : Installed 64-bit version.

source:http://linuxpoison.blogspot.com/2010/01/135781757113929.html

tutorial - iptstate - Display IPtables state information in a "top"-like interface

iptstate (IP Tables State) implements the "state top" feature from IP Filter for IP Tables. "State top" displays the states held by your stateful firewall in a "top"-like manner. Since IP Tables doesn't have a built-in way to easily display this information once, an option was added to iptstate to do this.

The only requirements are a curses library (usually ncurses), and libnetfilter_conntrack version 0.0.50 or later

Installation:
OpenSuSe user can install iptstate using "1-click" installer - here
Ubuntu user can install iptstate - here

After successful installation, go to terminal and type command: iptstate to open up the application and if netfilter CONNTRACK is enabled in the kernel.

source:http://linuxpoison.blogspot.com/2010/02/13578175718203.html

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