Linux User Guide

Need to monitor Linux server performance? Try these built-in command and a few add-on tools. Most Linux distributions are equipped with tons of monitoring. These tools provide metrics which can be used to get information about system activities. You can use these tools to find the possible causes of a performance problem. The commands discussed below are some of the most basic commands when it comes to system analysis and debugging server issues such as:

1. Finding out bottlenecks.
2. Disk (storage) bottlenecks.
3. CPU and memory bottlenecks.
4. Network bottlenecks.

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According to RFC2821 the lowest-numbered records are the most preferred MX for domain. So I’ve a target Postfix backup server to keep the messages in a queue waiting for the primary server to become available. This ensures that if my primary MX goes down I do not loss any emails. However, spammers are connecting to my backup MX to avoid anti spam filters that are running on the primary MX server. This also hides their real IP from my primary MX. How do I configure anti-spam for my backup RHEL / CentOS 5.3 based Postfix mx server?This is well known issue. Make sure your backup MX runs the same config in terms of spam rejection as your primary server. Try the following to improve backup eMail server anti spam configuration. (more…)

Q. How do I enable EPEL (Extra Packages for Enterprise Linux) repo and install the packages under RHEL / CentOS Linux?A. EPEL (Extra Packages for Enterprise Linux) is a volunteer-based community effort from the Fedora project to create a repository of high-quality add-on packages that complement the Fedora-based Red Hat Enterprise Linux (RHEL) and its compatible spinoffs, such as CentOS and Scientific Linux.EPEL provide lots of packages for CentOS / RHEL, It is not part of RedHat or CentOS but is designed to work with these major distributions. Please note that EPEL only provides free and open source software unencumbered by patents or any legal issues. In short you will not find mp3, dvd and music / media player under EPEL. However, you will find many programs related to networking, monitoring, sys admin, programming and so on. (more…)

Justin Silverton at Jaslabs has a supposed list of 10 tips for optimizing MySQL queries. I couldn’t read this and let it stand because this list is really, really bad. Some guy named Mike noted this, too. So in this entry I’ll do two things: first, I’ll explain why his list is bad; second, I’ll present my own list which, hopefully, is much better. Onward, intrepid readers!

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Q. I get a large amount of bin files in the MySQL data directory called “server-bin.n” or mysql-bin.00000n, where n is a number that increments. What is MySQL Binary Log? How do I stop these files being created?A. Usually /var/lib/mysql stores the binary log files. The binary log contains all statements that update data or potentially could have updated it. For example, a DELETE or UPDATE which matched no rows. Statements are stored in the form of events that describe the modifications. The binary log also contains information about how long each statement took that updated data.

The purpose of MySQL Binary Log

The binary log has two important purposes:

• Data Recovery : It may be used for data recovery operations. After a backup file has been restored, the events in the binary log that were recorded after the backup was made are re-executed. These events bring databases up to date from the point of the backup.
• High availability / replication : The binary log is used on master replication servers as a record of the statements to be sent to slave servers. The master server sends the events contained in its binary log to its slaves, which execute those events to make the same data changes that were made on the master.

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Synopsis: This is a cook book recipe on how to set up and run IP aliasing on a Linux box. In addition, there are instructions on how to also set up the machine to receive e-mail on the aliased IP #s.My setup:

• Latest kernel (2.0.27 - from ftp.funet.fi:/pub/Linux/kernel/src/v2.0) - has worked since 1.3.7x.
• IP Alias compiled as a loadable module. You would have indicated in the “make config” command to make your kernel, that you want the IP Masq to be compiled as a (M)odule. Check the Modules HOW-TO (if that exists) or check the info in /usr/src/linux/Documentation/modules.txt.
• I have to support 2 additional IPs over and above the IP already allocated to me.
• A D-Link DE620 pocket adapter (not important, works with any Linux supported network adapter).

Commands:

• First load the IP Alias module (you can skip this step if you compiled the module into the kernel):

  /sbin/insmod /lib/modules/`uname -r`/ipv4/ip_alias.o

• Second, setup the loopback, eth0 and all the IP #s beginning with the main IP # for the eth0 interface:

  /sbin/ifconfig lo 127.0.0.1/sbin/ifconfig eth0 up/sbin/ifconfig eth0 172.16.3.1/sbin/ifconfig eth0:0 172.16.3.10/sbin/ifconfig eth0:1 172.16.3.100

  172.16.3.1 is the main IP #, while .10 and .100 are the aliases. The magic is the eth0:x where x=0,1,2,…n for the different IP #s. The main IP # does not need to be aliased.

• Third, setup the routes. First route the loopback, then the net and, finally, the various IP #s starting with the default (originally allocated) one:

  /sbin/route add -net 127.0.0.0/sbin/route add -net 172.16.3.0 dev eth0/sbin/route add -host 172.16.3.1 dev eth0/sbin/route add -host 172.16.3.10 dev eth0:0/sbin/route add -host 172.16.3.100 dev eth0:1/sbin/route add default gw 172.16.3.200

That’s it. In the example IP # above, I am using the Private IP #s (RFC 1918) for illustrative purposes. Substitute them with your own official or private IP #s. (more…)

Multihop EBGP sessions are the traditional way to implement EBGP load balancing on parallel links. EBGP session is established between loopback interfaces of adjacent routers (see the next diagram; initial router configurations are included at the bottom of the article) and static routes (or an extra instance of a dynamic routing protocol) are used to achieve connectivity between loopback interfaces (BGP next-hops). The load balancing is an automatic result of the recursive route lookup of BGP next hops.

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The BGP daemon included in the Quagga suite provides an easy-to-configure source of BGP routes that you can use in your lab. Quagga BGP daemon has the following advantages over extra routers:

• It uses text configuration files that can be easily prepared and modified with external programs.
• The IP prefixes configured with the network command are advertised to the neighbors regardless of their presence in the IP routing table (Cisco IOS requires a matching entry in the IP routing table that you have to insert with an extra static route or interface IP address).
• Route-maps applied to the network command can set most BGP attributes, including AS path, extended communities and aggregator attributes.

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source : http://seotips4.com/seoblog/t241/

How many of you are still taking time and submitting to every directory you come across? Some sites offer a “Directory” section which lets members list their directories for you to submit sites too, sometimes you may find them via a huge blog list of XXXX directories to submit to. But how many of you take time, register and submit the details of your site over and over again in an attempt to gain the ever valuable backlink?

Previously directory submissions were a great way to build some solid backlinks. The trick now is most engines have updated their algorithms and started giving less weight to most of them, even being listed in big ones such as DMOZ and Yahoo isn’t what it used to be.

The problem with directories now is that they usually contain thousands of out bound links, sometimes they contain thousands of outbound links that go no where or to dead sites, or to bad sites such as “spammish” gambling and drug sites. Take that, and then the definition of a link farm, and you’ll see why most directories no longer carry any weight at all, and very few that carry some weight.

If the site is purely a directory, then chance of it giving you any bennefit is small. The directory will probably be nice and categorized, but then it’ll start getting deep down in folder structures for where your link will be placed. By the time the search engine spiders find your link, thats if they even crawl the page(s) its own, they won’t care about it.

However, some directories still continue to carry a small bit of weight for them, such as the Yahoo directory, the DMOZ directory and a few other of the larger human edited directories can still be benneficial in the link back category.

We of course don’t encourage anyone to sit around and submit their site to 500 directories, or even pay $99.99 for 1000 directory submissions. Instead, find which directories are still giving benefit of being listed in, and then try to get your site listed for that extra back link.

We’d love to hear your thoughts if you still submit to directories, be sure to leave a comment or head on over to our SEO Tips forum, and let us know there.

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