Tutorial Proggraming Free

tutorial - Tux3 Versioning Filesystem

"Since everybody seems to be having fun building new filesystems these days, I thought I should join the party, began Daniel Phillips, announcing the Tux3 versioning filesystem. He continued, "Tux3 is a write anywhere, atomic commit, btree based versioning filesystem. As part of this work, the venerable HTree design used in Ext3 and Lustre is getting a rev to better support NFS and possibly become more efficient." Daniel explained:

"The main purpose of Tux3 is to embody my new ideas on storage data versioning. The secondary goal is to provide a more efficient snapshotting and replication method for the Zumastor NAS project, and a tertiary goal is to be better than ZFS."

In his announcement email, Daniel noted that implementation work is underway, "much of the work consists of cutting and pasting bits of code I have developed over the years, for example, bits of HTree and ddsnap. The immediate goal is to produce a working prototype that cuts a lot of corners, for example block pointers instead of extents, allocation bitmap instead of free extent tree, linear search instead of indexed, and no atomic commit at all. Just enough to prove out the versioning algorithms and develop new user interfaces for version control."

The question is of course which file system will make the run: Tux3 is still at the beginning, while Btrfs could see a first beta in the next months. But there are still rumors that ZFS might be released under the GPL, and Hammer could also be implemented for Linux.

Either way, exciting times for file systems on Linux are ahead

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source:http://linuxpoison.blogspot.com/2008/08/13578175805960.html

tutorial - (r,w,x) Access Permissions For Files And Directories

Access Permission	File	Folder
Read (r)	Users can open and read the file.	Users can view the contents of the directory. Without this permission, users cannot list the contents of this directory with ls `-l`, for example. However, if they only have execute permission for the directory, they can nevertheless access certain files in this directory if they know of their existence.
Write (w)	Users can change the file: They can add or drop data and can even delete the contents of the file. However, this does not include the permission to remove the file completely from the directory as long as they do not have write permissions for the directory where the file is located.	Users can create, rename or delete files in the directory.
Execute (x)	Users can execute the file. This permission is only relevant for files like programs or shell scripts, not for text files. If the operating system can execute the file directly, users do not need read permission to execute the file. However, if the file must me interpreted like a shell script or a perl program, additional read permission is needed.	Users can change into the directory and execute files there. If they do not have read access to that directory they cannot list the files but can access them nevertheless if they know of their existence.

source:http://linuxpoison.blogspot.com/2008/08/135781758018681.html

tutorial - Quick and simple usage of tcpdump (packet sniffer)

Tcpdump is a popular computer network debugging and security tool which allows the user to intercept and display TCP/IP packets being transmitted or received over a network to which the computer is attached. Tcpdump allows us to precisely see all the traffic and enables us to create statistical monitoring scripts.

At an ethernet segment, tcpdump operates by putting the network card into promiscuous mode in order to capture all the packets going through the wire. Using tcpdump we have a view on any TCP/UDP connection establishment and termination and we can measure the response time and the packet loss percentagesTo print

Some simple usage:

all packets arriving at or departing from 192.168.0.2
# tcpdump -n host 192.168.0.2

To print traffic between 192.168.0.2 and either 10.0.0.4 or 10.0.0.5:
# tcpdump -n host 192.168.0.2 and $ 10.0.0.4 or 10.0.0.5 $

To print all IP packets between 192.168.0.2 and any host except 10.0.0.5:
# tcpdump ip -n host 192.168.0.2 and not 10.0.0.5

To print all traffic between local hosts and hosts at Berkeley:
# tcpdump net ucb-ether

To print all ftp traffic through internet gateway xx:
# tcpdump 'gateway xx and (port ftp or ftp-data)'

To print traffic neither sourced from nor destined for local hosts (if you gateway to one other net, this stuff should never make it onto your local net).
# tcpdump ip and not net localnet

To print the start and end packets (the SYN and FIN packets) of each TCP conversation that involves a non-local host.
# tcpdump 'tcp[13] & 3 != 0 and not src and dst net localnet'

To print IP packets longer than 576 bytes sent through gateway xx:
# tcpdump 'gateway xx and ip[2:2] > 576'

To print IP broadcast or multicast packets that were not sent via ethernet broadcast or multicast:
# tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224'

To print all ICMP packets that are not echo requests/replies (i.e., not ping packets):
# tcpdump 'icmp[0] != 8 and icmp[0] != 0"

source:http://linuxpoison.blogspot.com/2008/08/13578175806579.html

tutorial - Quick Configuration of AIDE (Advanced Intrusion Detection Environment)

AIDE (Advanced Intrusion Detection Environment) is a free replacement for Tripwire(tm). It generates a database that can be used to check the integrity of files on server. It uses regular expressions for determening which files get added to the database. You can use several message digest algorithms to ensure that the files have not been tampered with.

Default configuration of aide is quite fine. But we are going to tweak it slightly more.

Send the report

Reports which are created once a day can be sent to a custom address. you need to change the variable MAILTO to which ever address you like. Default is to send them to root on localhost.
To change it, open and edit /etc/default/aide

Configuring aide

Most AIDE configuration is in file /etc/aide/aide.conf. This file is pretty well documented and default rules are descent but we are going to make some slight changes.

AIDE aims at reporting files that changed since the last snapshot (/var/lib/aide/aide.db). A good security measure is to keep that file on a read-only device such as a floppy disk or a cdrom. If your machine has such a device, you could use the snapshot from that device. So let say that you have a copy of aide.db on a cdrom.

To use that snapshot, you could change:

database=file:/var/lib/aide/aide.db
to
database=file:/media/cdrom/aide.db

instead. That way, if an intruder get into your machine, he won’t be able to modify aide.db.

By default, AIDE checks for changes in Binaries and Libraries directories. Those changes are matched to the BinLib rule, which basically check for any changes in permissions, ownership, modification, access and creation date, size change, md5 and sha1 signature, inode, number of links and block count. Then, it also check for modifications in the log files against the rule Logs. Because log files tends to grow, you cannot use a signature there and you also have to asked aide not to check for size modification (S). Okie, this should be enough to get to understand how aide works. Reading through /etc/aide/aide.conf is a good place to learn more.

To make aide /etc/. To do so, added: /etc ConfFiles in /etc/aide/aide.conf, this will check for changes in /etc/.

Updating aide

aide is run on a daily basis through the script /etc/cron.daily/aide. Default settings in /etc/default/aide tells aide to update it’s database. Using database_out value in /etc/aide/aide.conf, aide is going to output a new database any time it runs in /var/lib/aide/aide.db.new if you kept the default settings.

Any time you will install new packages, change some configuration settings… it will be worth using an up-to-date database so aide won’t report any changes or addition in /etc/mynewsoft, /bin/mynewsoft …
So, when you install new softwares, make some configuration changes …, run:

# /etc/cron.daily/aide

Then, check in the report that modifications were only brought to the files you intended to modify and that added files are only coming from packages you have just installed.

Once you are sure that everything is fine, copy the new database to whatever place your database points to (cdrom, floppy, somewhere on you filesystem….).This way, you will get lighter reports next time aide runs.

source:http://linuxpoison.blogspot.com/2008/08/13578175806939.html

tutorial - How To increase the limit for file handles

There are cases when you get a lot of error messages about "running out of file handles", increasing this limit of this handler can solve this issue. To change the value, just write the new number into the file as below:

# cat /proc/sys/fs/file-max
8192

# echo 943718 > /proc/sys/fs/file-max

# cat /proc/sys/fs/file-max
943718

This value also can be changed using "sysctl" command. To make the change permanent, add the entries to /etc/sysctl.conf

# vi /etc/sysctl.conf
fs.file-max = 943718

source:http://linuxpoison.blogspot.com/2008/08/13578175803582.html

tutorial - PostgreSQL setup and configuration for md5 authentication

By default, connection via TCP/IP is disabled. And for authentication IDENT method is used. Please refer to the PostgreSQL Administrator's Guide..

To enable TCP/IP connections, edit the file /etc/postgresql//main/postgresql.conf

Locate the line #tcpip_socket = false and change it to tcpip_socket = true.

By default, the user credentials are not set for MD5 client authentication. So, first it is necessary to configure the PostgreSQL server to use trust client authentication, connect to the database, configure the password, and revert the configuration back to use MD5 client authentication. To enable trust client authentication, edit the file /etc/postgresql//main/pg_hba.conf

Comment out all the existing lines which use ident and MD5 client authentication and add the following line:

    local all postgres trust username

Then, run the following command to start the PostgreSQL server:

    sudo /etc/init.d/postgresql start

Once the PostgreSQL server is successfully started, run the following command at a terminal prompt to connect to the default PostgreSQL template database

    psql -U postgres -d template1

The above command connects to PostgreSQL database template1 as user postgres. Once you connect to the PostgreSQL server, you will be at a SQL prompt. You can run the following SQL command at the psql prompt to configure the password for the user postgres.

    template1=# ALTER USER postgres with encrypted password 'your_password';

After configuring the password, edit the file /etc/postgresql//main/pg_hba.conf to use MD5 authentication:

Comment the recently added trust line and add the following line:

    local all postgres md5 username

source:http://linuxpoison.blogspot.com/2008/08/13578175802333.html

tutorial - Building A Linux Filesystem From An Ordinary File

First, create a 20MB file (you could use any size for your FS) by executing the following command:

# dd if=/dev/zero of=disk-image count=40960
40960+0 records in
40960+0 records out
20971520 bytes (21 MB) copied, 0.225793 s, 92.9 MB/s

Next, to format this as an ext3 filesystem, you just execute the following command:
# /sbin/mkfs -t ext3 -q disk-image
disk-image is not a block special device.
Proceed anyway? (y,n)

Next, you need to create a directory that will serve as a mount point for the loopback device.
# mkdir fs

Now mount the this filesystem (file)
# mount -o loop=/dev/loop0 disk-image fs

Check if your FS is mounted
# mount
/dev/hda2 on / type ext3 (rw,noatime,acl,user_xattr)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
debugfs on /sys/kernel/debug type debugfs (rw)
udev on /dev type tmpfs (rw)
devpts on /dev/pts type devpts (rw,mode=0620,gid=5)
/dev/hda5 on /mnt/D type vfat (rw)
/dev/hda1 on /mnt/C type ntfs (rw)
/dev/hda7 on /cache type ext3 (rw,noatime)
/root/disk-image on /root/fs type ext3 (rw,loop=/dev/loop0)

Now, move to the mounted directory and create some directory and files on this new FS which we have created using file.
# ll
total 14
drwx—— 2 root root 12288 Apr 25 23:30 lost+found
drwxr-xr-x 2 root root 1024 Apr 25 23:33 nik
drwxr-xr-x 2 root root 1024 Apr 25 23:33 nikesh

source:http://linuxpoison.blogspot.com/2008/08/13578175713504.html

tutorial - running "rm -rf /"

source:http://linuxpoison.blogspot.com/2008/08/135781758014249.html

tutorial - How To Transfer existing Linux system to a new hard drive

For this we required Linux live disc (something like Knoppix Linux)

1) Hook up new drive. I used secondary master, hdc.

2) Reboot your system with live CD, this saves complications of dynamic directories and such.

3) Partition the drive with cfdisk or equivalent. Make sure you mirrored the existing setup, you can also have the new partitions with much larger size.

4) Time to format the new drives partitions (ext3, for example):

mkfs -t ext3 /dev/hdc1

mkswap /dev/hdc2

mkfs -t ext3 /dev/hdc3

5) Mount the partitions of old and new HD:

mkdir /mnt/oldmount /dev/hda1 /mnt/old

mkdir /mnt/newmount /dev/hdc1 /mnt/new

6) Copy the old partition onto the new one:

cp --recursive --verbose /mnt/old/bin /mnt/new/bin

7) Get a drink, take a walk, etc. This is going to take a while.

8) Repeat steps 5-7 as needed for other partitions.

9) Once it’s finished, check out the new fstab:

vi /mnt/new/etc/fstab

10) Verify that all the partitions are still arranged how you want them set up.

11) Run Grub on the new drive to make it bootable

Check here
exit

12) If all went well, you should be able to shut down, swap the new hard drive into the position of the old one, and boot into your much roomier new hard drive

source:http://linuxpoison.blogspot.com/2008/08/13578175711967.html

tutorial - Lighting up LAMP in Ubuntu 8.04 Hardy Heron

This guide will help newbies set up a fully working LAMP (Linux, Apache, MySQL, PHP) server using on Ubuntu 8.04 Hardy Heron. This will allow you to use various PHP applications such as the popular phpBB forums and WordPress blog in addition to the basic HTML pages and files.

Install Packages

First, install the required packages by typing the following into the terminal:

sudo apt-get install apache2 php5 libapache2-mod-php5 mysql-server libapache2-mod-auth-mysql php5-mysql phpmyadmin

This will install Apache, PHP, MySQL, their respective modules, and phpMyAdmin. Enter your preferred root password for mySQL when prompted and choose apache2 to be automatically configured.

If you’d like, you can test whether if Apache is working properly by going to http://localhost/ in your web browser.

Optionally, if you want computers on the same network to connect to the server you may want to edit /etc/mysql/my.cnf by invoking the command:

sudo gedit /etc/mysql/my.cnf

Then, replace the following line with your own IP address.

bind-address = 127.0.0.1

Configuring

To enable PHP and MySQL to work together, edit the php.ini file:

sudo gedit /etc/php5/apache2/php.ini

Then un-comment the following line. Save and close the file.

;extension = mysql.so

Accessing PHPMyAdmin

Edit the Apache configuration file:

sudo gedit /etc/apache2/apache2.conf

Add the following line to the bottom of the file. Save and close.

Include /etc/phpmyadmin/apache.conf

Restart Apache.

sudo /etc/init.d/apache2 restart

Testing PHP

Create and edit a file called testphp.php in your /var/www/ folder:

sudo gedit /var/www/testphp.php

Insert the following text inside that file and save:

Go back to your web browser and navigate to:

http://localhost/testphp.php

The PHP page should display. If a download window appears instead, something went wrong. Try reinstalling php5 and libapache2-mod-php5.

Testing phpMyAdmin

Navigate your web browser to:

http://localhost/phpmyadmin/

If the phpMyAdmin login page displays, then… You are done. That wasn’t so hard.

Now that you have LAMP running, why not try some applications?

Note: The root directory of your web server is /var/www/

Source: http://lijamez.wordpress.com/2008/06/02/lighting-up-lamp/

source:http://linuxpoison.blogspot.com/2008/08/13578175712268.html

tutorial - How to use/configure nscd for caching

nscd (Name Service Cache Daemon) is a GNU C Library -- A daemon which handles passwd, group and host lookups for running programs and caches the results for the next query. You should install this package only if you use slow Services like LDAP, NIS or NIS+

The nscd service comes as part of glibc , which means every Linux distribution will provide it. It is also extremely simple to set up. Once installed, edit the /etc/nscd.conf file to look similar to this:

server-user nscd
debug-level 0
reload-count unlimited
paranoia no
enable-cache passwd yes
positive-time-to-live passwd 3600
negative-time-to-live passwd 20
suggested-size passwd 211
check-files passwd yes
persistent passwd yes
shared passwd yes

enable-cache group yes
positive-time-to-live group 3600
negative-time-to-live group 60
suggested-size group 211
check-files group yes
persistent group yes
shared group yes

enable-cache hosts no

Now start the nscd service. The above configuration tells nscd to cache group and passwd entries and to let them persist for 3600 seconds.

Once nscd has started and has a few cached entries under its belt -- if you are already logged in and then disconnect from the network -- you will still be able to continue using the system just as if you were on the network -- apart from accessing shares and printers, utilising Kerberos, and performing new login sessions.

source:http://linuxpoison.blogspot.com/2008/08/13578175716279.html

tutorial - How to Manage disk Quotas for users

Quotas are defined per-filesystem. Most distros support quotas, although not all do it out-of-the-box, and you may have to install the quota package. To enable quota support, edit /etc/fstab as root and add the usrquota and grpquota options to the filesystems you wish to enable quota support for. For instance:

/dev/hda3 /home ext3 defaults,nosuid,nodev,usrquota,grpquota 1 2

Once you have made the changes, remount the filesystem(s) you have changed:

# mount -o remount /home

To check that quota support is indeed enabled, execute:

# quotacheck -augmv

This will instruct quotacheck to check all filesystems for user and group quotas without remounting them as read-only. Now you can enable quotas with the quotaon command:

# quotaon -augv

Once quotas have been turned on, use edquota to edit the quotas for a particular user:

# edquota -u nikesh

This will open the default system editor (usually vim) where you can edit the hard and soft limits for both blocks and inodes for each filesystem that supports quotas.

You can then view current quota usage by using the repquota tool:

# repquota -a

Once a soft quota has been exceeded, the user is notified once that they have exceeded their quota, but will be able to continue writing to the system unless they reach the hard quota; at which point, any new files created will be 0 bytes in size.

source:http://linuxpoison.blogspot.com/2008/08/13578175719232.html

tutorial - HTTP Response Codes

The following are webserver response codes that are used by webservers of all platforms.
Code     Description
100     Continue
101     Switching protocols
200     OK
201     Created
202     Accepted
203     Non-authoritative information
204     No content
205     Reset content
206     Partial content
300     Multiple choices
301     Moved permanently
302     Moved temporarily
303     See other
304     Not modified
305     Use proxy
307     Temporary redirect
400     Bad request
401     Unauthorized
402     Payment required
403     Forbidden
404     Not Found
405     Method not allowed
406     Not acceptable
407     Proxy authentication required
408     Request timeout
409     Conflict
410     Gone
411     Length required
412     Precondition failed
413     Request entity too large
414     Request URI too large
415     Unsupported media type
416     Requested range not satisfiable
417     Expectation failed
500     Internal server error
501     Not implemented
502     Bad gateway
503     Service unavailable
504     Gateway timeout
505     HTTP version not supported

source:http://linuxpoison.blogspot.com/2008/08/13578175717457.html

tutorial - Convert image formats using ImageMagick

The ImageMagick suite of programs allows you to manipulate images from the command-line, making it much simpler to convert large numbers of pictures or even for that single quick image conversion.

The convert tool is used to convert pictures from one format or size to another. The easiest method is to simply convert an image from one format to another using:

$ convert image.jpg image.png

This will convert image.jpg from a JPEG to a PNG and save it as image.png.

To convert and resize an image, use:

$ convert -size 50x50 image.jpg image.png

This will convert from JPEG to PNG format and resize the resulting image to 50x50 pixels. Likewise, you can use convert to rotate an image:

$ convert -rotate 90 image.jpg image.png

source:http://linuxpoison.blogspot.com/2008/08/135781757119506.html