Linux Administrator"s Guide

Determining a Server’s Functions

Ankit kumar — Sat, 14 Mar 2009 05:22:00 +0000

Before installing the Linux server, it can be useful to plan and determine exactly as to what purpose the server will serve. Even if you do not know all the functions available, it can give you an idea as to what is or isn’t required of the server you plan to install. A strategic planning ensure that the system has all the software it needs, and that it isn’t slowed down or made exploitable by having unnecessary software installed.

Step by Step
1. Consider each of the following questions, by making a list of services that are definitely needed or definitely not needed:

● Will this system’s disk resources will be accessible for mounting by other systems using NFS? Will it provide print services?

● Which Internet-related services will this server provide? For example, will it be used as a web server? Will it provide mail, IRC, newsgroup, or other such services?

● Will the system be a database server?

● Will the system perform authentication tasks such as running as an LDAP or NIS server?

● Will the system perform any network functions by performing routing, firewalling, SNMP or traffic monitoring, or the like?

● Will program development take place on this system? Which languages will be used? What compilers, debuggers, libraries, and utilities are necessary?

● How will remote users access the system? Do they need FTP or telnet access? Will SSH or rlogin or rsh be used?

● Will the system be accessible from the console, and if so, is the X Window System necessary? How much work will be done in the GUI, and which windowing environments are required?

2. Looking at the list of requirements, make a note of any components that are implied by the must-have items. For example, a web and database server may require tools to interface from the web pages to the database, so Perl or PHP might be useful.

3. What documentation needs to be installed on this system? If it will be a developer or end-user resource, there may be more documentation requirements than if it will be just one of many systems in a large server farm.

4. If this is a test server, what type of functions would you like to try? Make a note of each, and when it comes time to install the software, you may be able to find packages you didn’t know existed.

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Methods of Installation

Ankit kumar — Fri, 13 Mar 2009 12:50:00 +0000

As the connectivity and speed of both local area networks and Internet connections have increased a lot, so it is becoming an increasingly popular option to perform installations over the network rather than using a local CD-ROM.

In general, you’ll find that network installations becomes rather important once you’ve decided to install Linux over many machines and therefore requires a fast installation procedure in which many systems can be installed at the same time.

usually, server installations aren’t well suited to automation, because each server usually has a unique task to perform; thus, each server will have a slightly different configuration. For example, a server dedicated to handling logging information sent to it over the network is going to have especially large partitions set up for the appropriate logging directories, compared with a file server that performs no logging of its own.

Because of this, you might focus exclusively on the technique for installing a system from a CD-ROM. Of course, once you have gone through the process from a CD-ROM, you will find performing the network-based installations to be very straightforward.

If It Just Won’t Work Right . . .
Suppose you’ve gone through the installation procedure . . . twice. We said it should work. The installation manual said it should work. The Linux guru you spoke with last week in online forums said it should work.

But it’s just not working.

No operating system installs smoothly 100 percent of the time. (Yes, not even the Mac OS!) Hardware doesn’t always work as advertised, combinations of hardware conflict with each other, the CD-ROM might have CRC errors on i.

With Linux, you have several paths you can follow for help. If you have purchased your copy from a commercial vendor such as SuSE or Red Hat, you can always call tech support and reach a knowledgeable person who is dedicated to working through the problem with you. If you didn’t purchase a box set, you can purchase support from Red Hat and other distributors of Linux. Last, but certainly not least, is the option of going online for help. An incredible number of web sites like this are available to help you get started. They contain not only useful tips and tricks but also documentation and discussion forums where you can post your questions. Obviously, you’ll want to start with the site dedicated to your distribution: www.redhat.com for Red Hat Linux. Other distributions have their own sites.

Here are some recommended sites for installation help:
● comp.os.linux.admin
This is a newsgroup, not a web site. You can read it with a news client, or through the web at http://groups.google.com.

● comp.os.linux.redhat
this is another newsgroup, but Red Hat Linux–specific.

● linux.redhat
This is another Red Hat Linux newsgroup.

● http://www.linuxdoc.org/
This site is a collection of wonderful information about all sorts of Linux-related topics, including installation guides. Just a warning, though: Not all documents are up to date. Be sure to check the date of any document’s last update before following the directions. There is a mix of cookbook-style help guides as well as guides that give more complete explanations of what is going on.

● http://linuxnewbie.org/
This site features “Newbie-ized Help Files” that help with a variety of hardware and software issues.

And last but not the least share your problem with us we would surely try to find one or other way to your problem. There are many online forum for your support, infact you will always have such a large support for free with LINUX only.

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Dual-Booting Issues

Ankit kumar — Fri, 13 Mar 2009 03:40:00 +0000

If you are new to Linux, you may not be ready to commit to a complete system with Linux when you just
want a test drive. All distributions of Linux can be installed on only certain partitions of your hard disk while leaving others alone. Typically, this means allowing Microsoft Windows to coexist with Linux. So you can install Linux and Microsoft windows on same machine without any problem between the two.

Because we are focusing on server installations, this post will not cover the details of building a dual-booting system; however, anyone with a little experience in creating partitions on a disk should be able to figure this out. But anyways i will be including this in my later posts. If you are having difficulty, you may want to refer
to the installation guide that comes with your distribution.

Some quick hints:

If a Windows 95 or Windows 98 partition currently consumes an entirehard disk as drive C:, you can use the fips tool to repartition the disk. Simply defragment andthen run fips.exe.

If you are using Windows NT/2000 with NTFS and have already allocated all the disk with data on each partition, you may have to move data around a bit by hand to free up a partition.

Don’t bother trying to shrink an NTFS partition, though; because of its complexity, it doesn’t like being resized, and doing so will lead to corruption.

NOTE:-

From the perspective of flexibility, NTFS doesn’t sound like a good thing, but in reality it is. If you have to run a Windows server, use NTFS.

You may find using a commercial tool such as Partition Magic to be especially helpful, because it offers support for NTFS, FAT32, and regular FAT, as well as a large number of other file system types. Its user interface is also significantly nicer than fips.

If you’re going to be installing a dual-boot system, install Linux last. If you install Windows last, it will clobber the boot information for your Linux system. If you install Linux last, it will recognize that you have Windows installed and let you choose which one you want to boot by default.

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Uptime

Ankit kumar — Thu, 12 Mar 2009 10:43:00 +0000

All of these points about taking care of your servers and making sure silly things don’t cause them to crash from a long-time UNIX philosophy: Uptime is good. More uptime is better.

The UNIX (Linux) uptime command tells the user how long the system has been running since its last boot, how many users are currently logged in, and how much load the system is experiencing. The last two are useful measures that are necessary for day-to-day system health and long-term planning. (For example, the server load has been staying high lately, so may be it’s time to buy a faster/bigger/better server.)

But the all-important number is how long the server has been running since its last reboot. Long uptimes are a sign of proper care, maintenance, and, from a practical standpoint, system stability. You’ll often find UNIX administrators boasting about their server’s uptimes the way you hear car buffs boast about horsepower. This is also why you’ll hear UNIX administrators cursing at system changes (regardless of operating system) that require a reboot to take effect, even though applying the latest kernel security patch may justify that reboot. You may deny caring about it now, but in six months you’ll probably scream at anyone who reboots the system unnecessarily. Don’t bother trying to explain this phenomenon to a nonadmin, because they’ll just look at you oddly. You’ll just know in your heart that your uptime is better than theirs.

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Server Design

Ankit kumar — Thu, 12 Mar 2009 10:34:00 +0000

When a system becomes a server, its stability, availability, and performance become a significant issue. These three factors are usually improved through the purchase of more hardware, which is unfortunate. It’s a shame to pay thousands of dollars extra to get a system capable of achieving in all three areas when you could have extracted the desired level of performance out of existing hardware with a little tuning. With Linux, this is not hard. Even better, the gains are outstanding!

The most significant design decision you must make when managing a server configuration is not technical but administrative. You must design a server to be unfriendly to casual users. This means no cute multimedia tools, no sound card support, and no fancy web browsers (when at all possible). In fact, it should be a rule that casual use of a server is strictly prohibited— not only to site users but site administrators as well.

Another important aspect of designing a server is making sure that it has a good environment. As a system administrator, you must ensure the physical safety of your servers by keeping them in a separate room under lock and key (or the equivalent). The only access to the servers for nonadministrative personnel should be through the network. The server room itself should be well ventilated and kept cool. The wrong environment is an accident waiting to happen. Systems that overheat and nosy users who think they know how to fix problems can be as great a danger to server stability as bad software (arguably even more so).

Once the system is in a safe place, installing battery backup is also crucial. Backup power serves two key purposes: to keep the system running during a power failure so that it may gracefully shut down, thereby avoiding file damage or loss; and to ensure that voltage spikes, drops, and other noises don’t interfere with the health of your system.

Here are some specific things you can do to improve your server situation:
● Take advantage of the fact that the graphical user interface is uncoupled from the core operating system, and avoid starting the XWindow System (Linux’s GUI) unless someone needs to sit at the console and run an application. After all, like any other application, X requires memory and CPU time to work, both of which are better off going to the server processes instead.

● Determine what functions the server is to perform, and disable all other functions. Not only are unused functions a waste of memory and CPU, they complicate the process of securing the server.

● Unlike some other operating systems, Linux allows you to pick and choose the features you want in the kernel. The default kernel will already be reasonably well tuned, so you won’t have to worry about it; but if you do need to change a feature or upgrade the kernel, be picky about what you add and what you don’t. Make sure you really need a feature before adding it.

NOTE:-
You may hear an old recommendation that you recompile your kernel to make the most effective use of your system resources. This is no longer true—the only reason to recompile your kernel is to upgrade or add support for a new device. Remember: Once a server is in use, don’t change what’s stable and performs reasonably well without a good reason.

Using Tools to Monitor Security

Ankit kumar — Wed, 11 Mar 2009 04:50:00 +0000

Crackers — are people who, for purposes or to amuse themselves, like to break into other people’s computers — to steal information-are a clever bunch. If there is any vulnerability in a system, they will find it. Fortunately, the Linux development community is quick to find potential exploits and to find ways of slamming shut the door before crackers can enter. Fortunately, too, Red Hat is diligent in making available new, patched versions of packages in which potential exploits have been found. So your first and best security tool is making sure that whenever a security advisory is issued, you download and install the repaired package. This line of defense can be annoying, but it is nothing compared to rebuilding a compromised system.

And as good as the bug trackers are, sometimes their job is reactive. Preventing the use of your machine for bad purposes and guarding against intrusion are, in the end, your responsibility alone. Again, Red Hat Linux equips you with tools to detect and deal with unauthorized access of many kinds. In later posts, you’ll learn how to install and configure these tools and how to make sense of the warnings they provide. If your machine is connected to the Internet, you will be amazed at the number of attempts that are made to break into your machine.

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Configuring a Secure System

Ankit kumar — Wed, 11 Mar 2009 04:35:00 +0000

Linux Administrator”s most important duty is the , security of the computer and data integrity.

What does this mean? The system administrator’s most important task, first and foremost, is to make certain that no data on the machine or network are likely to become corrupted, whether by hardware or power failure, by misconfiguration, or by malicious or inadvertent intrusion from elsewhere.

Everyone involved in computing are aware of the increasing serious attacks upon machines connected to the Internet. The majority of these have not targeted Linux systems, but that doesn’t mean that Linux systems
have been entirely immune, either to direct attack or to the effects of attacks on machines running other operating systems.

In one such Distributed Denial of Service (DDoS) attack aimed at several major online companies, many of the “zombie” machines(Machines unknowingly used to spread malware without its owners consent ) — so that the vandals could employ thousands of machines instead of just a few — were running Linux that had not been patched to guard against a well-known security flaw. In the various “Code Red” attacks of the summer of 2001, Linux machines themselves were invulnerable, but the huge amount of traffic generated by this “worm” infection nevertheless prevented many Linux machines from getting much Web-based work done for several weeks, so fierce was the storm raging across the Internet. While these infection did not corrupt Linux machines as it did those running a different operating system.

Security can be as simple as turning off unneeded services, monitoring the Red Hat Linux security mailing list to make sure that all security advisories are followed, and otherwise engaging in good computing practices to make sure the system runs robustly. Or it can be an almost full-time job involving levels of security permissions within the system and systems to which it is connected, elaborate firewalling to protect not just Linux machines but machines that, through their use of non-Linux software, are far more vulnerable, and physical security — making sure no one steals the machine itself! For any machine that is connected to any other machine, security means hardening against attack and making certain that no one is using your machine as a platform for launching attacks against others. If you are running Web, ftp, or mail servers, it means giving access to those who are entitled to it while locking out everyone else. It means making sure that passwords are not easily guessed and not made available to unauthorized persons.

So your job as a system administrator is to strike just the right balance between maximum utility and maximum safety, all the while bearing in mind that confidence in a secure machine.

There are many tools that Red Hat Linux provides to help you guard against intrusion, even to help you prevent intrusion into non-Linux machines that may reside on your network. Linux is designed from the beginning with security in mind, and in all of your tasks you should maintain that same security awareness

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Monitoring and Tuning Performance

Ankit kumar — Sat, 07 Mar 2009 03:49:00 +0000

On a modern stand-alone system, Linux is pretty quick, and if it isn’t, there’s something wrong — something that is up to the system administrator to fix. You might have a number of people using the same fileserver,
mail server, or other shared machine, in which small improvements in system performance can mean a lot.

System tuning is an ongoing process carried by a variety of monitoringtools. Some performance decisions are made at installation time, while others are added or configured later.

Proper monitoring can detect a misbehaving application that might be consuming more system resources than it should or failing to exit completely on close. Through the use of system performance tools you can determine when hardware — such as memory, added storage, or even something as elaborate as a hardware RAID — should be upgraded for more cost-effective use of a machine in the enterprise. Possibly most important, careful system monitoring give you an early idea when a system component is showing early signs offailure, so that any potential downtime can be minimized.

Careful system monitoring and built-in configurability of Linux allows you to squeeze the best possible performance from your existing equipment, from customizing video drivers to applying special kernel patches to simply turning off unneeded services to free memory and processor cycles.

Backing Up and Restoring Files

Ankit kumar — Fri, 06 Mar 2009 04:14:00 +0000

Until equipments becomes absolutely failure proof, and until people lose their desire to harm the property of others for personal benefits (and, truth be known, until system administrators become perfect), there is always a need to back up important files and data so that in the event of a failure of hardware, security, or administration, the system can be up and running again with minimal disruption. Only the system administrator may do this.

(Because of its built-in security features, Linux may not allow users to be able even to back up their own files to floppy disks.)

Again, knowing that file backup is your job is not enough. You need to formulate a proper strategy for making sure your system is not vulnerable to disruption. If you have a high-capacity tape drive and several restore diskettes, you might make a full system backup in every few days. If you are managing a system with scores of users, It is more sensible to back up user accounts and system configuration files, from the distribution CDs. (Don’t forget the applications you’ve installed separately from your Red Hat Linux distribution, especially including anything heavily customized!)

Once you’ve decided what to back up, you need to decide how frequently to perform backups and whether you wish to maintain a series of incremental backups — adding only the files that have changed since the last backup — or multiple full backups, and when these backups are to be performed — do you trust an automated, unattended process?

A strategy should be the maintenance of perfect backups without ever needing to resort to them. This means encouraging users to keep multiple copies of their own important files, all in their home directories, so that you are not being asked to mount a backup so as to restore a file that a user has corrupted.(And if the system is stand-alone, you as your own system administrator might want to make a practice of backing up configuration and other important files.)

The chances are that even if you’re working for a company, you’ll make these decisions — all your boss wants is a system that works perfectly, all the time. Backing up is only half the story, too. You need to formulate a plan for bringing the system back up in the event of a failure.

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Creating and Maintaining User Accounts

Ankit kumar — Fri, 06 Mar 2009 03:44:00 +0000

Anyone cannot log on to a Linux machine. An account must be created for each user and — you guessed it — no one but the system administrator may do this. That’s simple enough.
But there are decisions that either you or your company must make. You might want users to select their own passwords, which would be easier for them to remember, but which probably would be easier for an external factor to crack. You might assign passwords, which is more secure in theory but which increases the chances that users will write them down on a conveniently located scrap of paper — a risk if many people have access to the area where the machine(s) is located. You might want that users must change their passwords periodically, and you can configure Red Hat Linux to prompt users to do so.

And what to do about old accounts? Perhaps someone has left the company. What happens to his or her account? You probably don’t want him or her to continue to have access to the company network. On the other hand, you don’t want to simply delete the account, because it might contain some essential data which is reside nowhere else.

There are aspects of your business that make World Wide Web access desirable, but you don’t want user”s spending their working hours surfing the Web.

The following issues and others are parts of the system administrator’s duties in managing user accounts. The administrator or his employer must establish the policies governing them— if in an enterprise, preferably in writing — for the protection of all concerned.

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