How to Use & Configure Google Public DNS on Linux System

When you use Google Public DNS, you are changing your DNS operator from your ISP to Google Public DNS.

In most cases, the IP addresses used by your ISP's domain name servers are automatically set by your ISP via the Dynamic Host Configuration Protocol (DHCP). To use Google Public DNS, you need to explicitly change the DNS settings in your operating system or device to use the Google Public DNS IP addresses. The procedure for changing your DNS settings varies according to operating system and version (Windows, Mac or Linux) or the device (computer, phone, or router).

Benefits and enhancements:
Performance: Many DNS service providers are not sufficiently provisioned to be able to support high-volume input/output and caching, and adequately balance load among their servers. In addition to load-balancing user traffic to ensure shared caching, Google Public DNS implements "smart" caching to increase the speed of responses. Google Public DNS independently resolves domain names and keeps the resolutions in the cache until their time-to-live (TTL) expires, at which point they are automatically refreshed. The cycle of caching and refreshing is performed offline, asynchronously with user requests, so that responses are almost always available directly from cache. 

Security: DNS is vulnerable to various kinds of spoofing attacks that can "poison" a nameserver's cache and route its users to malicious sites. The prevalence of DNS exploits means that providers have to frequently apply server updates and patches. In addition, open DNS resolvers are vulnerable to being used to launch denial-of-service (DoS) attacks on other systems. To defend against such attacks, Google has implemented several recommended solutions to help guarantee the authenticity of the responses it receives from other nameservers, and to ensure Google servers are not used for launching DoS attacks. These include adding entropy to requests, rate-limiting client traffic, and more. 

Correct results: Google Public DNS does its best to return the right answer to every query every time, in accordance with the DNS standards. Sometimes, in the case of a query for a mistyped or non-existent domain name, the right answer means no answer, or an error message stating the domain name could not be resolved. Google Public DNS never blocks, filters, or redirects users, unlike some open resolvers and ISPs.

Configuration:
Note: Before you change your DNS settings to use Google Public DNS, be sure to write down the current server addresses or settings on a piece of paper. It is very important that you keep these numbers for backup purposes, in case you need to revert to them at any time. 

The Google Public DNS IP addresses are as follows:

    8.8.8.8
    8.8.4.4

You can use either number as your primary or secondary DNS server. You can specify both numbers, but do not specify one number as both primary and secondary.

1) Edit /etc/resolv.conf:

sudo vi /etc/resolv.conf

2) Replace the nameserver lines with, or add, the following lines:

nameserver 8.8.8.8
nameserver 8.8.4.4

3) Save and exit.
4) Restart any Internet clients you are using.

Configuring DHCP client for dynamic ip address:
1) Edit /etc/dhclient.conf:

sudo vi /etc/dhclient.conf

2) If there is a line containing domain-name-servers, write down the IP addresses for future reference. Replace that line with, or add, the following line:

prepend domain-name-servers 8.8.8.8, 8.8.4.4;

2) Save and exit.
4) Restart your system.

Read more: http://linuxpoison.blogspot.com/2009/12/how-to-use-configure-google-public-dns.html#ixzz28hPhVv75

Pound Web server Load balancer

Install Pound to make the server load balancer.
This example shows to configure on the environment like follows
(1) www.server.world       [10.0.0.50]   Pound Server
(2) www01.server.world   [10.0.0.51]   Web Server#1 ( receive requests to www.server.world )
(3) www02.server.world   [10.0.0.52]   Web Server#2 ( receive requests to www.server.world )
(4) www03.server.world   [10.0.0.53]   Web Server#3 ( receive requests to www.virtual.host )
(5) www04.server.world   [10.0.0.54]   Web Server#4 ( receive requests to anything except them above )
[1] Install and Configure Pound

[root@www ~]#  yum --enablerepo=epel -y install Pound     # install from EPEL [root@www ~]#  vi /etc/pound.cfg # line 13: add ( log level - max=5 ) LogLevel 3 # line 14: add ( Interval of heartbeat - seconds ) Alive 30 # line 21-25: make it comments # ListenHTTPS #    Address 0.0.0.0 #    Port 443 #    Cert "/etc/pki/tls/certs/pound.pem" # End Service # for the requests to www.server.world HeadRequire "Host: .*www.server.world" BackEnd # backend server's IP address Address  10.0.0.51 # backend server's port Port  80 End BackEnd # backend server's IP address Address  10.0.0.52 # backend server's port Port  80 End End Service # for the requests to www.virtual.host HeadRequire "Host: .*www.virtual.host" BackEnd # backend server's IP address Address 10.0.0.53 # backend server's port Port 80 End End Service # for the requests to anything except them avobe HeadRequire "Host: .*" BackEnd # backend server's IP address Address 10.0.0.54 # backend server's port Port 80 End End [root@www ~]#  /etc/rc.d/init.d/pound start  Starting Pound: starting... [ OK ] [root@www ~]#  chkconfig pound on

[2]	Access to the Pound Server ( www.server.world ) with Web browser and make sure www01.server.world answers like follows.

[3]	Shutdown www01.server.world by manually, then www02.server.world answers like follows.

[4]	Access to the URI www.virtual.host, then www03.server.world answers like follows.

[5]	Access to the IP address directly, then www04.server.world answered.

Web server Load Balance Pen

Install Pen to configure Load Balance server. Pen is a light weight simple load balancer. This example shows to configure on the environment like follows.
        (1)  gw.horoppa.net         [10.0.0.50]  -  Pen Server
        (2)  www01.horoppa.net   [10.0.0.51]  -  Web Server#1
        (3)  www02.horoppa.net   [10.0.0.52]  -  Web Server#2
[1] Install and Configure Pen

[root@gw ~]#  yum --enablerepo=epel -y install pen     # install from EPEL [root@gw ~]#  vi /etc/pen.conf # create new # log file LOGFILE=/var/log/pen.log # output file of status WEBFILE=/var/www/pen/webstats.html # control port CONTROL=127.0.0.1:10080 # max connections MAX_CONNECTIONS=500 # listen port PORT=80 # number of backend servers BACKEND=2 # IP address of a backend SERVER1=10.0.0.51:80 # IP address of a backend SERVER2=10.0.0.52:80 [root@gw ~]#  vi /etc/rc.d/init.d/pend # create init script # this is an example #!/bin/bash # pend: Start/Stop Pend # chkconfig: - 90 10 # description: Pen is a light weight simple load balancer. # pidfile: /var/run/pen.pid . /etc/rc.d/init.d/functions . /etc/sysconfig/network . /etc/pen.conf LOCKFILE="/var/lock/subsys/pen" PID=/var/run/pen.pid PROG=/usr/bin/pen RETVAL=0 start() { echo -n $"Starting Pend: " SERVER=`grep "^SERVER" /etc/pen.conf | cut -d= -f2` daemon $PROG -w $WEBFILE -x $MAX_CONNECTIONS -p $PID -l $LOGFILE -C $CONTROL -S $BACKEND -r $PORT $SERVER RETVAL=$? echo [ $RETVAL -eq 0 ] && touch $LOCKFILE return $RETVAL } stop() { echo -n $"Stopping Pend: " killproc $PROG RETVAL=$? echo [ $RETVAL -eq 0 ] && rm -f $PID $LOCKFILE return $RETVAL } case "$1" in start) start ;; stop) stop ;; status) status pend ;; restart) stop start ;; *) echo $"Usage: $0 {start|stop|status|restart}" exit 1 esac exit $? [root@gw ~]#  vi /etc/logrotate.d/pen # setting of logrotation # this is an example /var/log/pen.log { daily copytruncate compress notifempty missingok postrotate /etc/rc.d/init.d/pend restart 2>&1 > /dev/null || true endscript } [root@gw ~]#  chmod 755 /etc/rc.d/init.d/pend  [root@gw ~]#  /etc/rc.d/init.d/pend start  Starting Pend: [ OK ] [root@gw ~]#  chkconfig --add pend  [root@gw ~]#  chkconfig pend on

[2]	Access to the URL you set and make sure backend server answers normally like follows.

[3]	Shutdown other httpd manually and make sure another httpd answers normally like follows.

[4]	Configure the tool that it's possible to watch Pen's status.

[root@gw ~]#  cp /usr/share/doc/pen-*/penstats /var/www/pen  [root@gw ~]#  vi /var/www/pen/penstats # line 4: change PIDFILE= /var/run/pen.pid # line 5: change WEBFILE= /var/www/pen/webstats.html [root@gw ~]#  vi /etc/httpd/conf.d/pen.conf # change Alias  /pen/ /var/www/pen/ <Directory /var/www/pen/>    DirectoryIndex penctl.cgi    Options ExecCGI    order deny,allow    deny from all    allow from 127.0.0.1  10.0.0.0/24     # IP address you permit </Directory> [root@gw ~]#  /etc/rc.d/init.d/httpd restart  Stopping httpd:  [ OK ] Starting httpd:  [ OK ] [root@gw ~]#  chmod 755 /var/www/pen/penstats  [root@gw ~]#  /var/www/pen/penstats > /dev/null     # run [root@gw ~]#  crontab -e # update by 5 minutes */5 * * * * /var/www/pen/penstats > /dev/null

[5]	Access to "http://(pen's hostname or IP address):(httpd listen port)/pen/webstats.html" and make sure following site is shown normally.

Subversion - Version Control

[1]	Install and Configure Subversion.

[root@www ~]#  yum -y install subversion mod_dav_svn [root@www ~]#  vi /etc/httpd/conf.d/subversion.conf # line 26-40: uncomment and change like follows <Location /repos>    DAV svn    SVNParentPath /var/www/svn # # Limit write permission to list of valid users.    <LimitExcept GET PROPFIND OPTIONS REPORT>       # Require SSL connection for password protection.       SSLRequireSSL       AuthType Basic       AuthName "Authorization Realm"       AuthUserFile  /etc/httpd/conf/.htpasswd        # specify access control file        AuthzSVNAccessFile /etc/svnusers       Require valid-user    </LimitExcept> </Location> [root@www ~]#  vi /etc/svnusers # set access right like an example below [site:/] # all users are writable * = rw # cent is writable [site:/directory] cent = rw # userB is readable userB = r # userC is not permitted userC = [root@www ~]#  mkdir -p /var/www/svn/site  [root@www ~]#  svnadmin create /var/www/svn/site     # create a repository [root@www ~]#  chown -R apache. /var/www/svn  [root@www ~]#  htpasswd -c /etc/httpd/conf/.htpasswd cent     # add a user New password: # set password Re-type new password: Adding password for user cent [root@www ~]#  /etc/rc.d/init.d/httpd restart  Stopping httpd: [ OK ] Starting httpd: [ OK ]

NFS Server

[1]	It's the Configuration on the system you want to build NFS server.

[root@dlp ~]#  yum -y install nfs-utils # install [root@dlp ~]#  vi /etc/idmapd.conf # line 5: uncomment and change to your domain name Domain =  horoppa.net [root@dlp ~]#  vi /etc/exports # write like below *note /home 10.0.0.0/24(rw,sync,no_root_squash,no_all_squash) # *note /home  ⇒ shared directory 10.0.0.0/24  ⇒ range of networks NFS permits accesses rw  ⇒ writable sync  ⇒ synchronize no_root_squash  ⇒ enable root privilege no_all_squash ⇒ enable users' authority [root@dlp ~]#  /etc/rc.d/init.d/rpcbind start  Starting rpcbind:  [  OK  ] [root@dlp ~]#  /etc/rc.d/init.d/nfslock start  Starting NFS statd:  [  OK  ] [root@dlp ~]#  /etc/rc.d/init.d/nfs start  RPC: Registered udp transport module. RPC: Registered tcp transport module. RPC: Registered tcp NFSv4.1 backchannel transport module. Installing knfsd (copyright (C) 1996 okir@monad.swb.de). Starting NFS services:  [  OK  ] Starting NFS daemon: NFSD: Using /var/lib/nfs/v4recovery as the NFSv4 state recovery directory NFSD: starting 90-second grace period [ OK ] Starting NFS mountd: [ OK ] [  OK  ] Starting RPC idmapd: [ OK ] [  OK  ] [root@dlp ~]#  chkconfig rpcbind on  [root@dlp ~]#  chkconfig nfslock on  [root@dlp ~]#  chkconfig nfs on

[2]	Configuration on NFS clients

[root@www ~]#  yum -y install nfs-utils # install [root@www ~]#  vi /etc/idmapd.conf # line 5: uncomment and change to your domain name Domain =  horoppa.net [root@www ~]#  /etc/rc.d/init.d/rpcbind start  Starting rpcbind:  [  OK  ] [root@www ~]#  /etc/rc.d/init.d/rpcidmapd start  Starting RPC idmapd: RPC: Registered udp transport module. RPC: Registered tcp transport module. RPC: Registered tcp NFSv4.1 backchannel transport module. [ OK ] [root@www ~]#  /etc/rc.d/init.d/nfslock start  Starting NFS statd:  [  OK  ] [root@www ~]#  /etc/rc.d/init.d/netfs start  Mounting other filesystems:  [  OK  ] [root@www ~]#  chkconfig rpcbind on  [root@www ~]#  chkconfig rpcidmapd on  [root@www ~]#  chkconfig nfslock on  [root@www ~]#  chkconfig netfs on  [root@www ~]#  mount -t nfs dlp.horoppa.net:/home /home  [root@www ~]#  df -h  Filesystem Size Used Avail Use% Mounted on /dev/mapper/VolGroup-lv_root 18G 864M 16G 6% / tmpfs 499M 0 499M 0% /dev/shm /dev/vda1 485M 47M 413M 11% /boot dlp.server.world:/home 18G 864M 16G 6% /home # home directory on NFS is mounted [root@www ~]#  vi /etc/fstab  # add at the lat line: change home directory this server mounts to the one on NFS /dev/mapper/VolGroup-lv_root / ext4 defaults 1 1 UUID=2078630e-e84a-49e7-af68-55f0bde8d6c3   /boot   ext4   defaults 1 2 tmpfs /dev/shm tmpfs defaults 0 0 devpts /dev/pts devpts gid=5,mode=620 0 0 sysfs /sys sysfs defaults 0 0 proc /proc proc defaults 0 0 dlp.horoppa.net:/home /home nfs defaults 1 1

Setting up multiple IP addresses on a single NIC in Linux

In linux, you can bind multiple IP addresses on a single NIC. This is usually done in case you are using your linux machine as a web server and is hosting multiple domains and you want to bind each domain to a unique IP address. This is how it is done.

Let us assume that you already have a NIC which is bound with a static IP address. Then you will have a file called /etc/sysconfig/network-scripts/ifcfg-eth0 .Myifcfg-eth0 file has the following entries:

# File: ifcfg-eth0
DEVICE=eth0
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.0.1
NETMASK=255.255.255.0
BROADCAST=192.168.0.255
NETWORK=192.168.0.0
HWADDR=00:80:48:34:C2:84

Now to bind another IP address to the same NIC, I create a copy of the above file ifcfg-eth0 and name it as ifcfg-eth0:1

# cd /etc/sysconfig/networking-scripts
# cp ifcfg-eth0  ifcfg-eth0:1

Now just change the values of the DEVICE and IPADDR in the file as follows:

# File: ifcfg-eth0:1
DEVICE=eth0:1
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.0.5
NETMASK=255.255.255.0
BROADCAST=192.168.0.255
NETWORK=192.168.0.0
HWADDR=00:80:48:34:C2:84

And lastly, restart the networking service. If you are using RedHat, then it is as simple as :

# service network restart

Note: If you do not know how to configure a NIC, see my previous posts - How to install a network card in Linux and How to assign an IP address.

Real-time Bandwidth monitoring tool - Bmon

bmon is a portable bandwidth monitor and rate estimator. It supports various input methods for different architectures. Various output modes exist, including an interactive curses interface, lightweight HTML output, and simple ASCII output. Statistics may be distributed over a network using multicast or unicast and collected at some point to generate a summary of statistics for a set of nodes.

Install bmon
For Ubuntu or Debian systems, either click this link or run the following command in a terminal

$ sudo apt-get install bmon

Using bmon:
Open a terminal and enter the command "bmon" and you should see the following output

Read more: http://linuxpoison.blogspot.com/2010/08/real-time-bandwidth-monitoring-tool.html#ixzz26olyOkMB

Lightweight Monitoring Tool for Servers and Embedded System - Monitorix

Monitorix is a free, open source, lightweight system monitoring tool designed to monitorize as many services as possible. At this time it monitors from the CPU load and temperatures to the users using the system. Network devices activity, network services demand and even the devices' interrupt activity are also monitored, and more.

The current status of any corporate server with Monitorix installed can be accessed via a web browser.
Monitorix has been designed to be used under production UNIX/Linux servers, but due its simplicity and small size you may also use it to monitor embedded devices.

Installation:
Monitorix is under GPLv2 licensing and available for download on the project homepage as source code and in numerous packages. Rpm based system (RedHat / Fedora / Centos / Opensuse) can install Monitorix using command:

rpm -ivh monitorix-1.4.2-1.noarch.rpm

Configuration of Monitorix:
Before starting the monitorix daemon, be sure to adjust the /etc/monitorix.conf to your liking. For a complete list of options and features, see the man page for monitor.conf.

our $TITLE = "Linux Poison";                                 # your company name
our $HOSTNAME = "poison.hell.com"; # hostname of this server
our $OSTYPE = "Linux-SuSE";                 # choose your OS type (see below)
our $SAMBAVER = "3";                         # Samba version (2 or 3)
our $MULTIHOST = "N";                 # Enable multihost feature
our $MULTIHOST_FOOTER = "Y";         # (multihost) display URL in image
our $MULTIHOST_IMGPERLINE = "2";         # (multihost) # of images per line
our $REPORT_LANG = "en";                         # Report language
our $THEME_COLOR = "black";                 # Default is "black", none is "white"
our $REFRESH_RATE = "150";                 # Web stats' refresh rate in seconds
our $ENABLE_CROND_MAIL = "Y";         # Error messages are sent by crond

Common settings to tweak here include company name, hostname, and theme color.

Finally you'll be able to start Monitorix with: # service monitorix start

To view your system stats, make sure your webserver is running and browse to [http://localhost/monitorix] to see the data.

Read more: http://linuxpoison.blogspot.com/2010/08/lightweight-monitoring-tool-for-servers.html#ixzz26olPYIpq