CentOS / RHEL Disk space re-sizing / Reallocation

Disk space rallocation in Linux-RHEL/CentoOS

Reducing the size of the /home/ from 500GB to 50GB and allocating it /root

scenario :

[root@cloud ~]# df -h /home/
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_cloud-LogVol00
                             12G  9.2G  1.9G  84% /home

Follow the steps :

Step 1:

unmount the the /home

[root@openstack ~]# umount /home/



Step 2:

check the filesystem for Errors using e2fsck command.





[root@openstack ~]# e2fsck -f /dev/mapper/vg_openstack-lv_home

e2fsck 1.41.12 (17-May-2010)

Pass 1: Checking inodes, blocks, and sizes

Pass 2: Checking directory structure

Pass 3: Checking directory connectivity

Pass 4: Checking reference counts

Pass 5: Checking group summary information

/dev/mapper/vg_openstack-lv_home: 11/3276800 files (0.0% non-contiguous), 251699/13107200 blocks

[root@openstack ~]#





Note: In the above command e2fsck , we use the option '-f' to forcefully check the filesystem , even if the filesystem is clean.




Step 3:

Shrink the size of /home to desire size.






[root@openstack ~]# resize2fs /dev/mapper/vg_openstack-lv_home 50G resize2fs 1.41.12 (17-May-2010) Resizing the filesystem on /dev/mapper/vg_openstack-lv_home to 13107200 (4k) blocks. The filesystem on /dev/mapper/vg_openstack-lv_home is now 13107200 blocks long.







Step 4:

Now reduce the size using lvreduce command.




[root@openstack ~]# lvreduce -L 50G /dev/mapper/vg_openstack-lv_home

  WARNING: Reducing active logical volume to 50.00 GiB

  THIS MAY DESTROY YOUR DATA (filesystem etc.)

Do you really want to reduce lv_home? [y/n]: y

  Reducing logical volume lv_home to 50.00 GiB

  Logical volume lv_home successfully resized





Step 5:

For the safer side , now check the reduced filesystem for errors

[root@openstack ~]# e2fsck -f /dev/mapper/vg_openstack-lv_home e2fsck 1.41.12 (17-May-2010) Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information /dev/mapper/vg_openstack-lv_home: 11/3276800 files (0.0% non-contiguous), 251699/13107200 blocks [root@openstack ~]#

Step 6:  

 Mount the file system and verify the size.

[root@openstack ~]# mount /home/
[root@openstack ~]# df -kh
Filesystem                        Size  Used Avail Use% Mounted on
/dev/mapper/vg_openstack-lv_root   50G  6.0G   41G  13% /
tmpfs                              16G  228K   16G   1% /dev/shm
/dev/sda1                         485M   40M  420M   9% /boot
/dev/mapper/vg_openstack-lv_home   50G  180M   47G   1% /home

Step 7:

Resize the desired partition with required space

lvextend -L 75G /dev/mapper/vg_openstack-lv_root

resize2fs /dev/mapper/vg_openstack-lv_root

check the sze of the partion changes 

df -kh

and you done resizing the partition.

Perl Important Tips

Perl  helpfull Trics/Tips:

1. Get all the Perl module installed via ubuntu/Linux command line

perl -MFile::Find=find -MFile::Spec::Functions -Tlw -e 'find { wanted => sub { print canonpath $_ if /\.pm\z/ }, no_chdir => 1 }, @INC'File::Find and File::Spec::Functions module are used to list all installed modules.

• -M option loads the module. It executes use module before executing the script
• -T option enables taint checking, which instructs perl to keep track of data from the user and avoid doing anything insecure with it. Here this option is used to avoid taking the current directory name from the @INC variable and listing the available .pm files from the directory recursively.
• -l option enables automatic line-ending processing in the output. Print statements will have the new line separator (\n) added at the end of each line.
• -w option prints any warning messages.
• -e option indicates that the following string is to be interpreted as a perl script (i.e., sequence of commands).

More simpler Way :

>find / -name \*.pm -type f
to know the pakage related to INC :

find `perl -e 'map {print "$_ "} @INC'` -name \*.pm -type f

2. View Perl Documentation From Unix Command Line

You can use either perldoc or man command to get help about a particular perl module as shown below.

$ perldoc Regexp::Common






(or)

$ man Regexp::Common

If the perl document is not enough, use perldoc option -m,  to view both source code and unformatted pod documentation of the specified perl module.

3.Verify Perl Module Is installed or not ?

Syntax: Perl -M"Module name" 

if it gives not Output i.e indicated that the module is installed, else it show an error stating the module not installed.

4.The flip-flop operator is useful for skipping the first iteration when looping through the records (usually lines) returned by a file handle, without using a flag variable:

while(<$fh>)
{
  next if 1..1; # skip first record
  ...
}

5.The null filehandle diamond operator <> has its place in building command line tools. It acts like <FH>to read from a handle, except that it magically selects whichever is found first: command line filenames or STDIN. Taken from perlop:

while (<>) {
...   # code for each line
}

6.Map 

The map built-in function is one of the most useful tools in your toolkit. map takes a list and applies a code block to every element, returning the list. You can think of it as stream processing: you push the list in one side and get it back on the other side with some transformation applied. Inside the code block, you refer to the current element with the traditional "$_" variable.

Example below demonstrate the function for perl code using map to conver the Uppercase .

my @l = qw(perl php python);
my @uc_l = map { uc($_) } @l;
# Result: PERL PHP PYTHON

7. ||= operator

In Perl, you can use the ||= operator. Its precedence rules are such that it’ll only do an      assignment if the value is false (‘false’ generally means zero, undefined, or the empty string):
$a ||= 5;

Perl interview questions

1. -c in perl shebang line
2. # significance in pelr shebacnk line
3. use strict usage and definition
4. diff between chop/chomp
5. . in regex in perl
6. is perl greedy ? justify
7. sort an array
8. uniq element in array ?
9. sort hash
10. Difference between referencing /dereferncing in perl
11. passing hashes in perl using subroutine
12. what are hashes of hashes
13. DB connection statement(fetch data) in perl
14. difference bw fetchrow_array/fetchrow_arrayref/fetchrow_hashref
15. <> ?
16. modes in files handling in perl .

Configuring Tomcat for CGI Perl

Configuring CGI  Perl in Apache Tomcat :

Software Requirement:

• Apache Tomcat 7.0.11 or above
• JDK 1.6 or above 
• Perl 5 or above

1. Download Tomcat. Install or unzip it to some directory.
2. Modify <TOMCAT_HOME>/conf/web.xml to uncomment the cgi servlet and its mapping

       uncomment:

 

<servlet>

 <servlet-name>cgi</servlet-name>

 <servlet-class>org.apache.catalina.servlets.CGIServlet</servlet-class>

 <init-param>

 <param-name>debug</param-name>

 <param-value>0</param-value>

 </init-param>

 <init-param>

 <param-name>cgiPathPrefix</param-name>

 <param-value>WEB-INF/cgi</param-value>

 </init-param>

 <init-param>

 

add the following:

<init-param>

 <param-name>passShellEnvironment</param-name>

 <param-value>true</param-value>

 </init-param>

 

now the CGI blocks look like:

 

 

<servlet>

 <servlet-name>cgi</servlet-name>

 <servlet-class>org.apache.catalina.servlets.CGIServlet</servlet-class>

 <init-param>

 <param-name>debug</param-name>

 <param-value>0</param-value>

 </init-param>

 <init-param>

 <param-name>cgiPathPrefix</param-name>

 <param-value>WEB-INF/cgi</param-value>

 </init-param>

 <init-param>

 <param-name>passShellEnvironment</param-name>

 <param-value>true</param-value>

 </init-param>

 <load-on-startup>5</load-on-startup>

</servlet>

 

3: Modify the servlet-mapping 

 

<servlet-mapping>

 <servlet-name>cgi</servlet-name>

 <url-pattern>/cgi-bin/*</url-pattern>

</servlet-mapping>

 

 

4:Modify <TOMCAT_HOME>\conf\context.xml to add a property on <Context>: 

 

<Context privileged="true">

...

</Context>

 

5.Create a cgi folder under <TOMCAT_HOME>/webapps/ROOT/WEB-INF/

 

mkdir <TOMCAT_HOME>/webapps/ROOT/WEB-INF/cgi

 

6. Create the CGI or Pl file under the same directory 

 

 <TOMCAT_HOME>/webapps/ROOT/WEB-INF/cgi/test.cgi

 

#!C:\Perl\bin\perl.exe

# filename: test1.cgi

print "Content-type: text/html\n\n";

print "Hello, world!\n"

 

7. Restart the Apache server

 

8: Open the link:http://localhost:8080/cgi-bin/test.cgi

 

  

 

 

 

 

 

 

Installing Cpan Module or installin perl Pakage

How to install perl pakage

There are many methods to install perl module or pakage to use in your program:

1. Using CPAN

Install cpan if not installed
to install a module say "Spreadsheet::Read" run the following command:

sudo cpan install module
Example:
sudo cpan install Spreadsheet::Read


2. With the help of the tar or zip file of the package 
follow the following steps:

download the tar of the package required from cpan directory
example for Spreadsheet::Read
go to cpan.org and search the module required.
write click on the tar of the module on the right side of the page and select coppy link location.
come to the terminal and run

1.wget http://search.cpan.org/CPAN/authors/id/H/HM/HMBRAND/Spreadsheet-Read-0.54.tgz
         this will download the package to the current location
extract the package
2.tar -xvzf pakagename
    tar -xvzf Spreadsheet-Read-0.54.tgz
3.cd Spreadsheet-Read-0.54
 on reaching inside the folder extracted run the following command
4.sudo perl Makefile.pl
5.make
6.sudo make install
and following these major steps you can easily install any pakage required.

Install Apache2 webserver with PERL,Php Support in Ubuntu Server(verified and tested)

Install Apache2 in Ubuntu

sudo aptitude install apache2

This will complete the installation.

After installation
Type the server’s IP address (or alias if you added the server to your /etc/hosts file) in your browser’s address bar or, if you are browsing on the server itself, type 127.0.0.1 or localhost. If an error occurs, then you will have to edit the apache2.conf file to ensure that Apache can fully resolve the server’s name.If you have any problem then you have to edit the apache2 configuration file using the following command

sudo nano /etc/apache2/apache2.conf
Add the following line somewhere
ServerName localhost
or
ServerName yourserverip
Save and exit the file

Restart Apache server using the following command.
sudo apache2ctl restart

Change default document root in Apache2
The main configuration file located at /etc/apache2/apche2.conf.If you want to change the default document root you need to edit the /etc/apache2/sites-available/default file and look for this line “DocumentRoot /var/www/” here you can change where ever you want to change.For example if you want to change /home/www the above line looks like this “DocumentRoot /home/www/”.
Save and exit the file

Restart Apache server using the following command.
sudo apache2ctl restart




Enable CGI and perl support for apache2 server
You need to install the following package

sudo aptitude install libapache2-mod-perl2

Configure a cgi-bin directory
You need to create a cgi-bin directory using the following command
sudo mkdir /home/www/cgi-bin
Configuring Apache to allow CGI program execution is pretty easy. Create a directory to be used for CGI programs and add the following to the site configuration file (again between the <VirtualHost> tags).

ScriptAlias /cgi-bin/ /home/www/cgi-bin/
<Directory /home/www/cgi-bin/>
Options ExecCGI
 AddHandler cgi-script cgi pl

       AddHandler default-handler .jpg .png .gif .js .txt .bat .css .html .htm

</Directory>

The first line creates an alias that points to the directory in which CGI scripts are stored. The final line tells Apache that only files that end with the *.cgi and *.pl extensions should be considered CGI programs and executed.

**AddHandler default-handler .jpg .png .gif .js .txt .bat .css .html .htm
this tells cgi to exclude some of the non perl related files like "CSS,txt,html etc"

Test your Perl Program
cd /home/www/cgi-bin
sudo nano perltest.pl
Copy and paste the following section save and exit the file.

###Start###
#!/usr/bin/perl -w
print "Content-type: text/html\r\n\r\n";
print "Hello there!<br />\nJust testing .<br />\n";

Change permissions on it

sudo chmod a+x perltest.pl
Open your web browser open
http://yourserverip/cgi-bin/perltest.pl.It should be working.








Enable PHP support for apache2 webserver
If you want to enable php5 or php4 support to your apache webserver use the following commands to install require packages
For PHP5

sudo aptitiude install php5 libapache2-mod-php5

For PHP4

sudo aptitiude install php4 libapache2-mod-php4

You also make sure the php5 and php4 modules are enabled using the following commands
sudo a2enmod php5
sudo a2enmod php4
After installing php support you need to restart apache webserver using the following command
sudo apache2ctl restart
Test your PHP Support foe apache webserver
To check the status of your PHP installation
sudo nano /var/www/testphp.php
and insert the following line

<?php phpinfo(); ?>

Save and exit the file
Now open web browser at http://yourserveripaddress/testphp.php and check.




Removing Apache2:

 cmd:

apt-get remove apache2

 

Setting Up GIT (git configuration on loca PC with the server)

Some Simple steps for GIT cloning and installation:

• sudo apt-get install git
• make a saparate folder for code
• cd into that
• git config --global user.name "XYZ" //user name of GIT account
• git config --global user.email "XYZ@gmail.com" //mail  which is registered with  GIT account
• NOTE:: each user have a unique user/mailid ., other wise git conflict will be there while git activities.
• git clone gitaccountwebpage.com/git/repository_name/   //clone to repository of git directory.
• once it done go to newly created directory synced with the server  (into your craeted directory).

GIt cloning Done


check basic commands like pull push add....

learn basics of GIT (http://rogerdudler.github.io/git-guide/)