Configure DHCP Server Step-by-Step config Guide Using Webmin

Dynamic Host Configuration Protocol (DHCP) is a client/server protocol that automatically provides an Internet Protocol (IP) host with its IP address and other related configuration information such as the subnet mask and default gateway.

In our previous article, you have setup your DNS Server using Webmin, refer below link for more information.

In this article We will seen how to configure DHCP Server Using Webmin(web-based interface). Webmin tool offer to new system administrators to perform all system management task from via a web browser, Instead of using the command line console or terminal. You can also manage a system from the console or remotely. Continue reading “Configure DHCP Server Step-by-Step config Guide Using Webmin” »

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Install ioncube on Linux server

  1. Begin by downloading the latest loaders to your computer from http://www.ioncube.com/loaders.php
  2. Extract the contents of the archived file on your local PC to a folder of your choice.
  3. Upload the folder IONCUBE via FTP to your domain webspace
  4. Now establish an SSH connection with server using a suitable client (e.g. Putty for PC’s or Terminal on Mac). This is usually done using the command: SSH rootusername@yourserver.com (you will then be asked for your password).
  5. You will need to browse to the public folder where you uploaded the IONCUBE directory (search internet for change and view directory commands in Unix).
  6. Move the ioncube folder to a permanent location by entering: mv ioncube /usr/local
  7. Next, you need to locate the php.ini file, to do this enter: locate php.ini – You should find it is in /usr/local/lib/php.ini. Now that you know the location of php.ini you need to edit it. pico /usr/local/lib/php.ini
  8. Now find where other zend extentions are in the file: ctrl + w: zend_extension
  9. Paste in your new line for ioncube loader: zend_extension = /usr/local/ioncube/ioncube_loader_lin_x.so (Replace x with your version of PHP eg. 4.4)
  10. Save the changes: ctrl + X then Y and enter
  11. Restart the web server to take effect: /etc/init.d/httpd restart

That’s it! Ioncube should now be installed & working on your server. To verify the installation was successful, check the PHP Info output for your server and you should see a new section which reads:

Additional Modules
Module Name ionCube Loader
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ip_conntrack table full, dropping packet

Last week, I found myself with a server under low load, but it couldn’t make or receive network connections. When I ran dmesg, I found the following line repeating over and over:

ip_conntrack: table full, dropping packet
I’d seen this message before, but I headed over to Red Hat’s site for more details. It turns out that the server was running iptables, but it was under a very heavy load and also handling a high volume of network connections. Generally, the ip_conntrack_max is set to the total MB of RAM installed multiplied by 16. However, this server had 4GB of RAM, but ip_conntrack_max was set to 65536:

# cat /proc/sys/net/ipv4/ip_conntrack_max
65536

I logged into another server with 1GB of RAM (RHES 5, 32-bit) and another with 2GB of RAM (RHES 4, 64-bit), and both had ip_conntrack_max set to 65536. I’m not sure if this is a known Red Hat issue, or if it’s just set to a standard value out of the box. Continue reading “ip_conntrack table full, dropping packet” »

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Reinstalling MySQL on CentOS/Redhat 6

Some time we faces issues with MySQL installation on Linux machine. If we simply remove MySQL packages and re-install doesn’t fixes the issue, in that case old settings may still exists on server which again affects new install. In that case first uninstall MySQL completely from system and erase all settings of old install. To do the same follow the below settings.

Note: Please do not use below steps if MySQL have any running databases.

Step 1: Uninstall MySQL Packages
First uninstall all the MySQL packages installed on your server

# yum remove mysql mysql-server

Step 2: Romove MySQL Directory
Now we need to remove MySQL data directory from system which by default exists at/var/lib/mysql. If you didn’t find this, It may be changed to some other place, which you can find in my.cnf file with variable datadir. Delete the /var/lib/mysql directory from system but we prefer to rename it to keep a backup of existing files.

# mv /var/lib/mysql /var/lib/mysql_old_backup Continue reading “Reinstalling MySQL on CentOS/Redhat 6” »

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How to Encrypt VNC Traffic with Putty

By default, VNC is not secure protocol.VNC uses encryption during initial connection and login (passwords are not sent in plain-text). Once, we connected then all the VNC data is unencrypted and hacker could sniff our VNC session. It is better (safer) to start VNC server only on 127.0.0.1(localhost) and tunnel it over secure SSH tunnel (For this,there are options in Putty).

In this example, I am using CentOS 6.2 as VNC server and VNC Viewer & PuTTY as VNC client on Windows 7.

On CentOS, edit /etc/sysconfig/vncservers file:

sudo nano /etc/sysconfig/vncservers

Add the option “-localhost“: Continue reading “How to Encrypt VNC Traffic with Putty” »

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How to Update SSH & MOTD Banner on CentOS 6

For legal reasons, Some people need to display a warning banner on their Linux machine before login so that a person requires to acknowledge the contents of the banner before entering the password. To do this, edit a/etc/issue.net file and fill it with the desired context.

Edit the  /etc/issue.net file:

sudo nano /etc/issue.net

001Here is mine banner as a sample, you can add your’s here:

#########################################################
# Authorized access only! # 
# Disconnect IMMEDIATELY if you are not an authorized user!!! #
# All actions Will be monitored and recorded #
###############################################################

Continue reading “How to Update SSH & MOTD Banner on CentOS 6” »

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IP Setting on CentOS6 using Shell Script

#!/bin/bash

if [ $# -eq 5 ]
then

echo ""
echo "Taking the backup and Changing the hostname from $(hostname) to $1 ..."

sed -i.bk "s/$(hostname)/$1/g" /etc/sysconfig/network

echo ""
echo "Backing up & Assigning the Static IP ..."
echo ""

cp /etc/sysconfig/network-scripts/ifcfg-$2 /etc/sysconfig/network-scripts/$2.bk

cat <<EOF > /etc/sysconfig/network-scripts/ifcfg-$2

DEVICE=$2
BOOTPROTO=static
IPADDR=$3.$4
NETMASK=255.255.255.0
GATEWAY=$3.$5
ONBOOT=yes
EOF

echo "Changing the dns ..."
echo ""

sed -i.bk "s/nameserver.*/nameserver $3.$5/" /etc/resolv.conf

echo "Adding $1 as hostname to the /etc/hosts file .."
echo ""

sed -i.bk "/$(hostname)$/d" /etc/hosts
echo "$3.$4 $1" >> /etc/hosts

echo "Restarting the Network Service, Please connect it using the new IP Address if you are using ssh ..."

service network restart

else

echo "Usage: ip.sh <hostname> <interface> <baseip> <ipaddress> <gateway/dns>"
echo "Example: ip.sh testname eth0 10.10.10 41 1"

fi
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Install Zenoss on CentOS 6 64bit

zenoss-3Minimal Hardware Requirements:

Small Deployments (1 to 250 Monitored Devices)

  • 4GB RAM
  • 2 CPU Cores
  • 1x 300GB, 10K RPM Drive

Medium Deployments (250 to 500 Monitored Devices)

  • 8GB RAM
  • 4 CPU Cores
  • 1x 300GB, 10K RPM Drive

Large Deployments (500 to 1000 Monitored Devices)

  • 16GB – 32GB RAM
  • 8 CPU Cores
  • 1x 300GB, 15K RPM Drive

Disable SELinux and IPtables

For this guide SELinux and IPtables were completely disabled and CentOS 6 was up-to-date!

Add DNS FQDN Entry and NTP Sync

To ensure proper resolving FQDN entries in DNS or /etc/hosts must exist and please configure NTP time synchronization for services to run properly. Continue reading “Install Zenoss on CentOS 6 64bit” »

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NFS Firewall

Dynamic ports cannot be protected by port filtering firewalls such as iptables. First, you need to configure NFS services to use fixed ports. Open /etc/sysconfig/nfs, enter:

# vi /etc/sysconfig/nfs

Modify config directive as follows to set TCP/UDP unused ports:

# TCP port rpc.lockd should listen on.
LOCKD_TCPPORT=lockd-port-number
# UDP port rpc.lockd should listen on.
LOCKD_UDPPORT=lockd-port-number 
# Port rpc.mountd should listen on.
MOUNTD_PORT=mountd-port-number
# Port rquotad should listen on.
RQUOTAD_PORT=rquotad-port-number
# Port rpc.statd should listen on.
STATD_PORT=statd-port-number
# Outgoing port statd should used. The default is port is random
STATD_OUTGOING_PORT=statd-outgoing-port-number

Continue reading “NFS Firewall” »

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NFS Server and Client on CentOS

Assumptions:

NFS Server IP: 172.16.5.100
NFS Client Node1: 172.16.5.101
NFS Client Node2: 172.16.5.102
NFS Client Node3: 172.16.5.103
NFS Client Node4: 172.16.5.104

On the NFS Server & All Client machine as well:

yum install nfs-utils nfs-utils-lib

Edit the exports file that shows what to share and with whom. So run: Continue reading “NFS Server and Client on CentOS” »

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