Tutorial Proggraming Free

tutorial - How to recover damaged Superblock

If a filesystem check fails and returns the error message “Damaged Superblock”

Solution:
There are backups of the superblock located on several positions and we can restore them with a simple command. Backup locations are: 8193, 32768, 98304, 163840, 229376 and 294912. ( 8193 in many cases only on older systems, 32768 is the most current position for the first backup )

Now, suppose you get a ¨Damaged Superblock¨ error message at filesystem check ( after a power failure ) and you get a root-prompt in a recovery console, then you give the command:

# e2fsck -b 32768 /dev/hda5

System will then check the filesystem with the information stored in that backup superblock and if the check was successful it will restore the backup to position 0.

If this is not working try using the other copy of Superblock located at the above mention location in your HD.

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source:http://linuxpoison.blogspot.com/2007/10/13578175801555.html

tutorial - How to crash Linux?

As root, you can do whatever you want.

Try this command, as root (reconsider if you really want to crash):

# cp /dev/zero /dev/men

As root, you can even erase all the files on your system with a similarly innocuously looking one-liner (don’t do it):

# rm -rf /

This is not to say that Linux is easy to crash, but that the system administrator (”root”) has the complete power over the system so think before when working on Linux as “root” user.

source:http://linuxpoison.blogspot.com/2007/10/13578175803052.html

tutorial - How To Make ISO image from CD

Use following command to create ISO image of CD
Note: /dev/hdc is my cdrom device
1. dd if=/dev/hdc of=/home/nikesh/example.iso bs=2048 conv=notrunc
— OR –

2. cat /dev/hdc > /home/nikesh/example.iso
Both commands do exactly the same, but the first one might be easier to remember.

source:http://linuxpoison.blogspot.com/2007/10/135781758019245.html

tutorial - Quick Apache configuration tips

Enable Directory Browsing

Options +Indexes## block a few types of files from showingIndexIgnore *.wmv *.mp4 *.avi

Disable Directory Browsing

Options All -Indexes

Customize Error Messages

ErrorDocument 403 /forbidden.html
ErrorDocument 404 /notfound.html
ErrorDocument 500 /servererror.html

Get SSI working with HTML/SHTML

AddType text/html .html
AddType text/html .shtml
AddHandler server-parsed .html
AddHandler server-parsed .shtml
# AddHandler server-parsed .htm

Change Default Page (order is followed!)

DirectoryIndex myhome.htm index.htm index.php

Block Users from accessing the site

order deny,allow
deny from 202.54.122.33
deny from 8.70.44.53
deny from .spammers.com
allow from all

Allow only LAN users

order deny,allow
deny from all
allow from 192.168.0.0/24

Redirect Visitors to New Page/Directory

Redirect oldpage.html http://www.domainname.com/newpage.html
Redirect /olddir http://www.domainname.com/newdir/

Block site from specific referrers

RewriteEngine on
RewriteCond %{HTTP_REFERER} site-to-block\.com [NC]
RewriteCond %{HTTP_REFERER} site-to-block-2\.com [NC]
RewriteRule .* - [F]

Block Hot Linking/Bandwidth hogging

RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$RewriteCond %{HTTP_REFERER} !^http://(www\.)?mydomain.com/.*$ [NC]
RewriteRule \.(gif|jpg)$ - [F]

Want to show a “Stealing is Bad” message too?

Add this below the Hot Link Blocking code:

RewriteRule \.(gif|jpg)$ http://www.mydomain.com/dontsteal.gif [R,L]

Stop .htaccess (or any other file) from being viewed

order allow,deny
deny from all

Avoid the 500 Error

# Avoid 500 error by passing charset
AddDefaultCharset utf-8

Grant CGI Access in a directory

Options +ExecCGI
AddHandler cgi-script cgi pl# To enable all scripts in a directory use the following#
SetHandler cgi-script

Change Script Extensions

AddType application/x-httpd-php .gne

gne will now be treated as PHP files! Similarly, x-httpd-cgi for CGI files, etc.

Use MD5 Digests

Performance may take a hit but if thats not a problem, this is a nice option to turn on.

ContentDigest On

Save Bandwidth

# Only if you use PHP

php_value zlib.output_compression 16386

Turn off magic_quotes_gpc

# Only if you use PHP

php_flag magic_quotes_gpc off

source:http://linuxpoison.blogspot.com/2007/11/13578175805448.html

tutorial - Sync Samba and Unix password

The pam_smbpass PAM module can be used to sync users’ Samba passwords with their system passwords. If a user invokes the passwd command, the password he uses to log in to the system as well as the password he must provide to connect to a Samba share are changed.

To enable this feature, add the following line to /etc/pam.d/system-auth below the pam_cracklib.so invocation:

password required /lib/security/pam_smbpass.so nullok use_authtok try_first_pass

source:http://linuxpoison.blogspot.com/2007/11/13578175804608.html

tutorial - How to use rsysnc to keep files in Sync Between Servers

Suppose remote computer is “192.168.1.171″ and has the account “don”. You want
to “keep in sync” the files under “/home/Logs” on the remote computer with files on “/home/nikesh/Server” on the local computer.

$ rsync -Lae ssh don@192.168.1.171:/home/Logs /home/nikesh/Server

“rsync” is a convient command for keeping files in sync, and as shown above, it will work
through ssh. The -L option tells rsync to treat symbolic links like ordinary files.

Also see [http://www.rsnapshot.org/]

source:http://linuxpoison.blogspot.com/2007/11/135781758018003.html

tutorial - Recover MySQL database root password

You can recover MySQL database server password with following five easy steps.

Step # 1: Stop the MySQL server process.

Step # 2: Start the MySQL (mysqld) server/daemon process with the –skip-grant-tables option so that it will not prompt for password

Step # 3: Connect to mysql server as the root user

Step # 4: Setup new root password

Step # 5: Exit and restart MySQL server

Here are commands you need to type for each step (login as the root user):

Step # 1 : Stop mysql service

# /etc/init.d/mysql stop

Stopping MySQL database server: mysqld.

Step # 2: Start to MySQL server w/o password

# mysqld_safe –skip-grant-tables &

[1] 5988

Starting mysqld daemon with databases from /var/lib/mysql

mysqld_safe[6025]: started

Step # 3: Connect to mysql server using mysql client

# mysql -u root

Output:Welcome to the MySQL monitor. Commands end with ; or \g.Your MySQL connection id is 1 to server version: 4.1.15-Debian_1-logType ‘help;’ or ‘\h’ for help. Type ‘\c’ to clear the buffer.

mysql>

Step # 4: Setup new MySQL root user password

mysql> use mysql;

mysql> update user set password=PASSWORD(”NEW-ROOT-PASSWORD“) where User=’root’;

mysql> flush privileges;

mysql> quit

Step # 5: Stop MySQL Server:

# /etc/init.d/mysql stop

Stopping MySQL database server: mysqld STOPPING server from pid file /var/run/mysqld/mysqld.pid
mysqld_safe[6186]: ended
.
[1]+ Done mysqld_safe –skip-grant-tables

Step # 6: Start MySQL server and test it

# /etc/init.d/mysql start

# mysql -u root -p

source:http://linuxpoison.blogspot.com/2007/11/135781758017736.html

tutorial - BackUp and Restore MBR after Windows messes it up

Just another note about restoring the boot loader for dual boot systems, after Windows messes it up. In Linux, the “dd” command can read and write to/from raw disks and files. If you have a floppy drive, creating a boot disk is as simple as putting a floppy in the drive and typing this:

[You need to use "root" account to do following]

# dd if=/dev/hda of=/dev/fd0 bs=512 count=1

This makes an exact copy of the MBR of the first hard drive (hda - you need to replace this), copying it to a floppy disk. You can boot directly from this floppy, and see your old boot menu. You can restore it by switching the “if=” and “of=” (input file, output file) parameters.

If you don’t have a floppy drive, you can back it up to a file with this:

# dd if=/dev/hda of=/home/nik/boot.mbr bs=512 count=1

Then you can boot into a CD-ROM distribution such as Knoppix, or often use your Linux distribution’s installation CD to boot into rescue mode and restore it with:

# dd if=/mnt/hda5/nik/boot.mbr of=/dev/hda bs=512 count=1

(you’ll need to find and mount the partition containing the directory where you backed up the MBR).

source:http://linuxpoison.blogspot.com/2007/11/135781758017343.html

tutorial - Install multimedia Support in Fedora 8

Follow these instructions to get mp3 and other multimedia support on your Fedora Core 8.

Open a terminal and become root, then run this command:

# wget http://livna-dl.reloumirrors.net/fedora/8/i386/livna-release-8-1.noarch.rpm
# rpm -ivh livna-release-8-1.noarch.rpm

Install all other plug ins..

# yum -y install gstreamer-plugins-bad gstreamer-plugins-ugly xine-lib-extras-nonfree

source:http://linuxpoison.blogspot.com/2007/11/13578175802537.html

tutorial - How to Encrypt - Decrypt your files

To Encrypt a normal file:
$ openssl des3 -salt -in myfile.txt -out outputfile.des3
[This will ask for password, give any pass that you can remember]

To Decrypt:
$ openssl des3 -d -salt -in outputfile.des3 -out myfile.txt -k password

source:http://linuxpoison.blogspot.com/2007/11/13578175807530.html

tutorial - How to do Virtual hosting in Vsftpd

There are two ways of doing this ...

1. If you integrate vsftpd with xinetd, you can use xinetd to bind to several different IP addresses. For each IP address, get xinetd to launch vsftpd with a different config file. This way, you can get different behavior per virtual address.

2. Alternatively, run as many copies as vsftpd as necessary, in standalone
mode. Use “listen_address=x.x.x.x” to set the virtual IP.

source:http://linuxpoison.blogspot.com/2007/11/135781758014672.html

tutorial - Prevent the reuse of old passwords

The PAM module pam_unix.so can be configured to maintain a list of old passwords for every user prohibiting the reuse of old passwords.

The list is located in the /etc/security/opasswd file. This is not a plain text file, but it should be protected the same as the /etc/shadow file. This is normally referred to as password history.

To remember the last 5 passwords, add the line below to the /etc/pam.d/system-auth file:

password sufficient /lib/security/pam_unix.so use_authtok md5 shadow remember=5

source:http://linuxpoison.blogspot.com/2007/11/13578175802121.html

tutorial - Temporarily suspend a process

At times, you may find it necessary to temporarily suspend a process, and then resume its execution at a later time. The following two commands will suspend a process, and the resume it, respectively:

# kill -STOP 945
# kill -CONT 945

source:http://linuxpoison.blogspot.com/2007/11/13578175805781.html

tutorial - How to add a module to an existing kernel

Sometime you need to add a new driver to a modular kernel, you can just compile the needed module and install it without recompiling the entire kernel. Just follow these steps:

# cd /usr/src/linux (location where linux kernel source is stored)
# make config Or make menuconfig OR make xconfig
(Choose the driver as a module)

# make dep
# make modules
# make modules_install
# depmod -a

You should now be able to use the new module.

source:http://linuxpoison.blogspot.com/2007/11/13578175809945.html

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