Solr is highly reliable, scalable and fault tolerant, providing distributed indexing, replication and load-balanced querying, automated failover and recovery, centralized configuration and more. Solr powers the search and navigation features of many of the world’s largest internet sites.

In this tutorial I will explain How to install Solr 4.10.4 on CentOS 6.5. The first of all, Login as root user.

Installing JAVA

To start things off first check if you have Java installed:

# which java

If you do not have Java installed check for latest version:

# yum list available | grep openjdk

Outputs

java-1.6.0-openjdk.x86_64                  1:1.6.0.34-1.13.6.1.el6_6     updates
java-1.6.0-openjdk-demo.x86_64             1:1.6.0.34-1.13.6.1.el6_6     updates
java-1.6.0-openjdk-devel.x86_64            1:1.6.0.34-1.13.6.1.el6_6     updates
java-1.6.0-openjdk-javadoc.x86_64          1:1.6.0.34-1.13.6.1.el6_6     updates
java-1.6.0-openjdk-src.x86_64              1:1.6.0.34-1.13.6.1.el6_6     updates
java-1.7.0-openjdk-demo.x86_64             1:1.7.0.75-2.5.4.0.el6_6      updates
java-1.7.0-openjdk-devel.x86_64            1:1.7.0.75-2.5.4.0.el6_6      updates
java-1.7.0-openjdk-javadoc.noarch          1:1.7.0.75-2.5.4.0.el6_6      updates
java-1.7.0-openjdk-src.x86_64              1:1.7.0.75-2.5.4.0.el6_6      updates
java-1.8.0-openjdk.x86_64                  1:1.8.0.31-1.b13.el6_6        updates
java-1.8.0-openjdk-demo.x86_64             1:1.8.0.31-1.b13.el6_6        updates
java-1.8.0-openjdk-devel.x86_64            1:1.8.0.31-1.b13.el6_6        updates
java-1.8.0-openjdk-headless.x86_64         1:1.8.0.31-1.b13.el6_6        updates
java-1.8.0-openjdk-javadoc.noarch          1:1.8.0.31-1.b13.el6_6        updates
java-1.8.0-openjdk-src.x86_64              1:1.8.0.31-1.b13.el6_6        updates

Type the following command to install java

# yum install java-1.8.0-openjdk.x86_64

Finally, check Java version:

# java -version
java version "1.8.0_75"
OpenJDK Runtime Environment (rhel-2.5.4.0.el6_6-x86_64 u75-b13)
OpenJDK 64-Bit Server VM (build 24.75-b04, mixed mode)
[root@host-129-19 ~]# 

Installing Solr

Install the latest version Solr release by downloading from http://www.us.apache.org/dist/lucene/solr/

# cd /opt/
# wget http://www.us.apache.org/dist/lucene/solr/4.10.4/solr-4.10.4.tgz

Extracting solr package:

# tar zxvf solr-4.10.4.tgz
# mv solr-4.10.4 solr

Renaming “example” directory to project name, example “core”:

# cd solr
# mv example core

Running Solr

You should now be able to test running the Solr server with following command

# cd /opt/solr/core
# java -jar start.jar

If everything works correctly you should be able to view the Solr server admin by going to:
http://[server hostname or IP]:8983/solr/
If this does not work try viewing the log /opt/solr/solr/logs/solr.log

Auto Start Apache Solr

First, create script for handling the Solr server service

# vi /etc/init.d/solr

And add the following script

#!/bin/sh 
# chkconfig: 2345 95 20 
# description: Solr Server 
# Solr Server service start, stop, restart 
# @author Shay Anderson 10.13 

SOLR_DIR="/opt/solr/core" 
JAVA="/usr/bin/java -DSTOP.PORT=8079 -DSTOP.KEY=a09df7a0d -jar start.jar" 
LOG_FILE="/opt/solr/core/logs/solr-server.log" 

case $1 in 
      start) 
            echo "Starting Solr..." 
            cd $SOLR_DIR 
            $JAVA 2> $LOG_FILE & 
            sleep 3 
            ;; 
      stop) 
            echo "Stopping Solr..." 
            pkill -f start.jar > /dev/null 
            RETVAL=$? 
            if [ $RETVAL -eq 0 ]; then 
                  echo "Stopped" 
            else 
                  echo "Failed to stop" 
            fi 
            ;; 
      restart) 
            $0 stop 
            sleep 2 
            $0 start 
            ;; 
      *) 
            echo "Usage: $0 [start|stop|restart]" 
            exit 1 
            ;; 
esac 

exit 0

To run Apache Solr by default when the system boots, type the following command

# chmod +x /etc/init.d/solr
# chkconfig --level 345 solr on

The post How To Install Solr 4.10.4 On CentOS 6.5 appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

Have you ever made a mistake and changed permissions of the folder and all it’s subfolders? And how to change back permissions of files/folders to default state ?

Yesterday , I accidentally changed / (ROOT) permission to 777 with following command

# chmod 777 -R /

After that, All files and folders on my server changed to 777 permissions. And I try to reboot my server, I can’t login into my server. It’s shown error:

Failed to start SSH server : Starting sshd:WARNING: UNPROTECTED PRIVATE KEY FILE! Permissions 0775 for '/etc/ssh/ssh_host_key' are too open. It is recommended that your private key files are NOT accessible by others. This private key will be ignored. bad permissions: ignore key: /etc/ssh/ssh_host_key Could not load host key: /etc/ssh/ssh_host_key
...

How do I fix it ?

If you can boot your system into Single User Mode, then type 2 commands

# for p in $(rpm -qa); do rpm --setperms $p; done
# for p in $(rpm -qa); do rpm --setugids $p; done

Above command combination will reset all the permissions to the default permissions under CentOS / RHEL / Fedora Linux.

If you can’t boot into Single User Mode, Let boot from CentOS installation CD into Recuse Mode, make sure that your system mounted into /mnt/sysimage, And type the following command

# chmod 7777 -R /mnt/sysimage/

Note: Permission is 7777 not 777
To change all files and folder to “7777” permission. And reboot your system. After that, You can boot into Single User Mode and type above commands.

Reset default permissions of all files and folders under /home/

Type the following commands

# cd /home/
# for p in $(ll); do chown $p.$p -R /home/$p; done
# find . -type d -print0 | xargs -0 chmod 755
# find . -type f -print0 | xargs -0 chmod 644
# chmod 700 *

Reset default permissions of all files and folders of MySQL (/var/lib/mysql)

Type the following commands

# chown mysql.mysql -R /var/lib/mysql
# cd /var/lib/mysql
# find . -type d -print0 | xargs -0 chmod 700
# find . -type f -print0 | xargs -0 chmod 660
# chmod 777 *.sock

Finally, restart MySQL with following command

# /etc/init.d/mysqld restart

The post How To Restore Default Permissions Of All Files Under / (ROOT) appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

The virsh command is an alternative command to manage a Red Hat Enterprise Linux 5 KVM environment using a Command Line Interface(CLI). The virsh command is provided as part of the libvirt API which provides a common API to applications requiring standardized access to interact with KVM using a stable interface.

The following are basic and commonly used virsh commands:

help	 print help
list	 list domains
create	 create a domain from an XML file
start	 start a previously created inactive domain
destroy	 destroy a domain
define	 define (but do not start) a domain from an XML file
domid	 convert a domain name or UUID to domain id
domuuid	 convert a domain name or id to domain UUID
dominfo	 domain information
domname	 convert a domain id or UUID to domain name
domstate domain state
quit	 quit this interactive terminal
reboot	 reboot a domain
restore	 restore a domain from a saved state in a file
resume	 resume a domain
save	 save a domain state to a file
shutdown gracefully shutdown a domain
suspend	 suspend a domain
undefine undefine an inactive domain

List running guest VMs

Type the following command:

# virsh list

Sample outputs:

Id  Name                 State
----------------------------------
1   VM01                 running
2   VM02	         running

Staring a guest VM

Type the following command:

# virsh start VM01

Shutddowwn a guest VM

Type the following command:

# virsh shutdown VM01

Or, you can forcefully stop a guest VM with following command:

# virsh destroy VM01

Rebooting a guest VM

Type the following command:

# virsh reboot VM01

The post How To Start / Shutdown / Reboot Guest Operating Systems With virsh Command On KVM appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

What’s Discard Protocol ?

The Discard Protocol is a service in the Internet Protocol Suite defined in RFC 863. It is intended for testing, debugging, and measurement purposes.
A host may send data to a host that supports the Discard Protocol on either Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) port number 9. The data sent to the server is simply discarded. No response is returned.

Install Discard on Centos

What we need is the TCP Discard service on port 9. Xinetd has it built-in, so we can just use that. Make sure that the following definition is available in xinetd’s configuration file(s), usually /etc/xinetd.d/discard. It should contain a service like the following:

service discard
{
    type            = INTERNAL
    id              = discard-stream
    socket_type     = stream
    protocol        = tcp
    user            = root
    wait            = no
    disable         = no
    FLAGS           = IPv6 IPv4
}

Note: socket_type = stream using for TCP and socket_type = dgram using for UDP

Restart xinetd to reread the configuration files and activate the new discard service. Type the following command:

# /etc/init.d/xinetd restart

The post How To Install TCP Discard Service appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

PHP: Hypertext Preprocessor is a widely used, general-purpose scripting language that was originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document. As a general-purpose programming language, PHP code is processed by an interpreter application in command-line mode performing desired operating system operations and producing program output on its standard output channel. It may also function as a graphical application. PHP is available as a processor for most modern web servers and as a standalone interpreter on most operating systems and computing platforms. (wikipedia.org)

PHP works with apache, lighttpd, nignx and other webservers and PHP is very easy to install.

Installing PHP on CentOS

if you would like to install PHP on CentOS use yum command

yum install php

Updating PHP on CentOS

if you would like to update PHP on CentOS use yum command

yum update php

Install & Update PHP latest version

Default the system will be installed php with stable version, but if you wanted to install or update PHP with latest version then you need to create /etc/yum.repos.d/centos-test.repo and enter following lines in it:

[c5-testing]
name=CentOS-5 Testing
baseurl=http://dev.centos.org/centos/5/testing/$basearch/
enabled=1
gpgcheck=1
gpgkey=http://dev.centos.org/centos/RPM-GPG-KEY-CentOS-testing

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Runlevels define what services or processes should be running on the system. The Linux operating system can make use of runlevels through the programs of the sysvinit project. After the Linux kernel has booted, the init program reads the /etc/inittab file to determine the behavior for each runlevel. Unless the user specifies another value as a kernel boot parameter, the system will attempt to enter (start) the default runlevels.

Runlevels on RedHat, Centos and Fedora have 6 levels:

Runlevel 0: Halt System - To shutdown the system
Runlevel 1: Single user mode
Runlevel 2: Basic multi user mode without NFS
Runlevel 3: Full multi user mode (text based)
Runlevel 4: unused
Runlevel 5: Multi user mode with Graphical User Interface
Runlevel 6: Reboot System

Change Runlevels

Use the init command to change run levels:

init <level>

On most Linux server default run level 3 and on most Linux desktop default run level 5 with GUI. The default run level is defined in /etc/inittab file. You can change default run level by edit /etc/inittab file.

vi /etc/inittab

The following line at the top line of inittab file

id:3:initdefault:

Change default run level from 3 to 5:

id:5:initdefault:

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chkconfig provides a  simple  command-line  tool  for  maintaining  the/etc/rc[0-6].d  directory  hierarchy by relieving system administrators of the task of directly manipulating the  numerous  symbolic  links  in those directories.

chkconfig has five distinct functions: adding new services for  management,  removing  services  from management, listing the current startup information for services, changing the  start-up  information  for  services, and checking the start-up state of a particular service.

Synopsis

chkconfig --list [name]
chkconfig --add name
chkconfig --del name
chkconfig [--level levels] name <on|off|reset>
chkconfig [--level levels] name

Example

List status for all services

chkconfig --list

List status for test service

chkconfig --list test

Add service called test

chkconfig --add test

Delete service called test

chkconfig --del test

Turn on & Turn off service

chkconfig --level 3 5 httpd off

The command above will turn off httpd service in run levels 3 and 5.

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