Install memcached on Centos 6.x

Install Memcached package on
Fedora 16/15/14/13/12, CentOS/Red Hat (RHEL) 6.2/6.1/6

yum install memcached

Configure memcached
Most important value to configure is CACHESIZE, which is cache size on Megabytes. On all systems, particularly 32-bit, ensure that you leave enough room for both memcached application in addition to the memory setting. For example, if you have a dedicated memcached host with 4GB of RAM, do not set the memory size above 3500MB. Failure to do this may cause either a crash or severe performance issues. Example Following configuration use 3072 Mb memory for Memcached:

vi /etc/sysconfig/memcached
PORT="11211"
USER="memcached"
MAXCONN="1024"
CACHESIZE="3072"
OPTIONS=""

Start Memcached
# Set Memcached to start automatically on boot
chkconfig memcached on
# Start Memcached
/etc/init.d/memcached start
## OR ##
service memcached start

Check that Memcached is Running and Working
echo stats | nc localhost 11211

Open Memcached Port (11211) on Iptables Firewall (If the Memcached will also be used other local servers)
Edit /etc/sysconfig/iptables file:
nano -w /etc/sysconfig/iptables
Add following line before COMMIT:
-A INPUT -m state --state NEW -m tcp -p tcp --dport 11211 -j ACCEPT
Restart Iptables Firewall:
service iptables restart
## OR ##
/etc/init.d/iptables restart
Test remote connection:
echo stats | nc memcache_host_name_or_ip 11211


appendix:

To flush all the data from Memcached using command line:

echo "flush_all" | nc 127.0.0.1 11211

How to generate an SSH key with Linux?

You can generate a SSH key in Linux using the ssh-keygen command. You should run it in the command line. You will be asked for a file in which the key should be saved to and for a passphrase (password) for the key:

user@localhost: ssh-keygen -t dsa
Generating public/private dsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_dsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in id_dsa.
Your public key has been saved in id_dsa.pub.
The key fingerprint is:
16:8e:e8:f2:1d:c9:b9:cf:43:9a:b3:3c:c1:1f:95:93 user@localhost

This will create a private key written to /home/user/.ssh/id_dsa and a public key written to/home/user/.ssh/id_dsa.pub. The passphrase is used to protect your key. You will be asked for it when you connect via SSH.

Installing Apache, MySQL, PHP in CentOS 5.5 on Rackspace Cloud

Most of cloud users prefer Rackspace Cloud for its better service and cost effectiveness…
All commands are performed as root to install Apache, MySQL, PHP in CentOS 5.5 Server on Rackspace Cloud.

Install Apache

# sudo yum install httpd mod_ssl

Configure ServerName
# sudo /etc/init.d/httpd start

Remove Error
Starting httpd: httpd: Could not reliably determine the server’s fully qualified domain name, using xx.xx.xxx.xx for ServerName

Modify
# sudo vi /etc/httpd/conf/httpd.conf

Add server name after #ServerName www.example.com:80

ServerName svnlabs

# sudo /etc/init.d/httpd reload

By default port 80 is blocked on server, enable in iptables…
# iptables -I RH-Firewall-1-INPUT -p tcp –dport 80 -j ACCEPT

Chkconfig to start automatically if the Cloud Server is rebooted.

# sudo /sbin/chkconfig httpd on

Install MySQL

# yum install mysql-server
# /etc/init.d/mysqld start

Install PHP

Edit Repo file
# sudo vi /etc/yum.repos.d/CentOS-Base.repo

add at last

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

now run
# yum install php php-common php-gd php-mcrypt php-pear php-pecl-memcache php-mhash php-mysql php-xml php-mbstring

Install PhpMyAdmin

# cd /var/www/html
# wget http://downloads.sourceforge.net/project/phpmyadmin/phpMyAdmin/3.3.6/phpMyAdmin-3.3.6-english.tar.gz?r=http%3A%2F%2Fwww.phpmyadmin.net%2Fhome_page%2Fdownloads.php&ts=1283745912&use_mirror=voxel

# tar zxvf phpMyAdmin-3.3.6-english.tar.gz
# mv phpMyAdmin-3.3.6-english phpmyadmin
# cd phpmyadmin
# cp config.sample.inc.php config.inc.php

Edit config.inc.php for random string $cfg['blowfish_secret'] = ‘RandomStringHere’;

Restart server
# service httpd restart

use the following in the file config.inc.php of phpMyAdmin to restrict access to from remote machines:

$cfg['Servers'][$i]['AllowDeny']['order'] = 'deny,allow';
$cfg['Servers'][$i]['AllowDeny']['rules'][] = 'allow % from 127.0.0.1';
$cfg['Servers'][$i]['AllowDeny']['rules'][] = 'deny % from all';

This means that only users logged into my laptop are allowed to see the phpMyAdmin pages in their browser. The percent sign (%) stands for "all users".

How to restart my-sql-Server

Each distribution comes with a shell script (read as service) to restart / stop / start MySQL server. First login as root user and open shell prompt (command prompt).

Login as root user. Now type the following command as per your Linux distro:

A) If you are using mysql on RedHat Linux (Fedora Core/Cent OS) then use following command:

* To start mysql server:

/etc/init.d/mysqld start

* To stop mysql server:

/etc/init.d/mysqld stop

* To restart mysql server

/etc/init.d/mysqld restart

Tip: Redhat Linux also supports service command, which can be use to start, restart, stop any service:

# service mysqld start
# service mysqld stop
# service mysqld restart

(B) If you are using mysql on Debian / Ubuntu Linux then use following command:

* To start mysql server:

/etc/init.d/mysql start

* To stop mysql server:

/etc/init.d/mysql stop

* To restart mysql server

/etc/init.d/mysql restart

Howto disable recursive DNS queries

Recursive DNS queries occur when a DNS client requests information from a DNS server that is set to query subsequent DNS servers until a definitive answer is returned to the client. The queries made to subsequent DNS servers from the first DNS server are iterative queries.

Thus keeping recursive query can lead to  unauthorized use of resources and DOS attacks.

To disable Recursive DNS follow the steps:

1) SSH server as root and edit file /etc/named.conf

root@server[~]#vi /etc/named.conf

2) add line recursion no; in options clause and it will look something like.

options {

directory “/var/named”;

dump-file “/var/named/data/cache_dump.db”;

statistics-file “/var/named/data/named_stats.txt”;

/*

* If there is a firewall between you and nameservers you want

* to talk to, you might need to uncomment the query-source

* directive below.  Previous versions of BIND always asked

* questions using port 53, but BIND 8.1 uses an unprivileged

* port by default.

*/

// query-source address * port 53;

recursion no;

};

3) Now restart or reload named service.

root@server[~]#/etc/init.d/named reload