LINUX NEWS
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Thursday, September 20, 2001
Read By Over 7,000 Linux Enthusiasts Weekly!TABLE OF CONTENTS
1) Sean’s Notes
2) Linux News
Hacking Linux Exposed
Linux+ Exam Details
Write a Game, Win the Loot
IPStor package lifts storage to new capacities3) Linux Resources
But Who Will Support it?
And is it Supported?
Separated by a Common Operating System
Mandrake Demos and Tutorials
Heat Emergency4) App o’ the week
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1) Sean’s Notes
Going through my list of common questions, I found a good one:
“I can ping a host by IP, but not by name”.
Many would immediately jump to the conclusion that something must be wrong with the DNS settings, and they’d probably be right. But, where do you set up the DNS server in Linux?
Before I jump into all the configuration files, some things have to be said about naming. Like Windows, DNS isn’t the only way to name a computer. NIS, the Network Information Service, can be used to store the mappings, as can NIS+ (an advanced version made by SUN), text files, and many others. As with Windows, there is a pecking order of sorts: one database is consulted before another, and the searching stops once a match is found.
Unlike Windows, though, it’s pretty trivial to change all of this by editing one file. The C library implements a call named “gethostbyname”, which is used universally in UNIX to find out the address of a machine given its name. Note that “address” can be pretty much anything – we’re not limiting ourselves to IP addresses. One of the things that gethostbyname() does is to consult a line in /etc/nsswitch.conf to find out where it should start looking.
nsswitch.conf keeps a line for each of several databases, including the password file, keys, protocols, and yes, hostnames. On my system, I see a line with
hosts: files nisplus dns
This is processed in order. First, my system will look in a particular file. For names, it’s /etc/hosts. No match? Check out NIS+. I’m not using NIS+, so it will go to DNS. If it can find a match in DNS, then great, return that. Otherwise, the host isn’t found. By playing with the order, you can change the precedence of the lookups, or even remove a map entirely (i.e., you can set up your computer to only use NIS+ for, say, name resolution).
Once the library has decided to use DNS, it has to know what server to use. To find this out, it consults /etc/resolv.conf. This file can further alter the behaviour several ways.
Nameservers are listed with the “nameserver” keyword:
nameserver 1.2.3.4 nameserver 5.6.7.8
will allow the use of two nameservers for DNS resolution. By default, they are tried in the order listed, so 5.6.7.8 will only get consulted if 1.2.3.4 times out.
The “options rotate” command will allow you to round-robin between your listed nameserver.
Those who have configured DNS on Windows machines will likely remember the “domain name” and “search order” options. If my domain is “example.com”, it would be desirable to try to find hosts within that domain if they fail elsewhere. Thus, a query to the name “test” will first be tried as “test”, and then “test.example.com”. Set your default domain name with
domain example.com
If you would like additional domains added to this list, use the “search” keyword. (note that “domain” is a special form of “search”)
search example.org
Thus, if “test” isn’t found in example.com, it will be tried in example.org. Be careful using this, though, as it will start to generate a lot of DNS traffic as the searchlist grows.
So, in quick summary, /etc/nsswitch.conf tells the system where to look for various things. If it is to look in files, /etc/hosts is where the names are kept. If it has to go to DNS, /etc/resolv.conf is consulted for more info.
Solaris users should be especially wary of nsswitch.conf, as by default, DNS isn’t in there (at least before Solaris 7). Either add it in, or look at the other nsswitch.* files for a template to copy over.
DNS is only part of the way that the system resolves names. Understanding the whole process of resolution can help you troubleshoot.
Long live the Penguin,
Sean swalberg@brainbuzz.com
2) Linux News
Hacking Linux Exposed
This time around, I review “Hacking Linux Exposed”, a comprehensive book on Linux and network security. If you’re in the market for a book on security, give this one serious consideration.
http://itresources.brainbuzz.com/tutorials/tutorial.asp?t=S1TU1442
Linux+ Exam Details
Many of you are familiar with the A+ exam from CompTia, along with all the other certs they offer such as Server+, Network+, and more. Did you know they offer Linux+? The beta period closed some time ago, and the exam is almost ready to go live. Brainbuzz user bcabalic dug up all the details on the format and costs in case you were wondering.
http://boards.brainbuzz.com/boards/vbm.asp?m64351
Write a Game, Win the Loot
No Starch press, Loki Software, and Linux Journal bring you a contest to go with the release of their “Programming Linux Games” book (review coming soon!). The best SDL based game that fits under a Meg gets some really neat prizes, not to mention the bragging rights. There are other restrictions to encourage people to join, so give it a look!
http://www.nostarch.com/?games
IPStor package lifts storage to new capacities
If you thought SANs (Storage Area Networks) were limited to big systems, think again. This Linux based product acts as a SAN, providing geographically disperse, redundant disk storage. The cool thing is the way that it uses drivers on the clients to map the IP address to a local SCSI device… No expensive fibre channel cards!
http://www.zdnet.com/products/stories/reviews/0,4161,2806610,00.htm l
3) Linux Resources
But Who Will Support it?
One of the harder things to pitch to the suits is the support aspect of Linux. There are many companies that will support your developers, desktop, and servers. ZDNet was kind enough to perform a detailed review of 12 different vendors, and even give us all the data.
http://techupdate.zdnet.com/techupdate/stories/main/0%2c14179%2c280 8791-1%2c 00.html
And is it Supported?
Making sure hardware is supported by Linux can be a daunting task. The Hardware HOWTO is a comprehensive list of hardware that is supported under the standard kernel, or by third parties. It’s also good in that it tells you if the driver is distributed in binary or source format. Binary is fine, but imposes difficulties when trying to change your kernel version.
http://www.ibiblio.org/pub/linux/docs/howto/Hardware-HOWTO
Separated by a Common Operating System
This article starts off by following the author’s trial of Debian and SuSE, and ends up finding out that they’re completely different. Not only are they different from each other, but also he finds that most distributions have major differences and incompatibilities. Is this a sort of accidental fragmentation? At this point, the only common thing through distributions is the kernel itself, but is this necessarily a bad thing?
http://www.linuxplanet.com/linuxplanet/opinions/3543/1/
Mandrake Demos and Tutorials
Not being a Mandrake user myself, I was impressed at the depth of this part of their site. They have demos of some of their software, basic tutorials for newbies, and other highlights. If you’re interested in seeing what Mandrake has to offer, but don’t have the time to try an install, this is certainly be a good place to start.
http://www.linux-mandrake.com/en/demos/
Heat Emergency
As you might have deduced from the increasing size of heatsinks and fans, CPUs these days generate a lot of heat. What would happen if the CPU overheated? Someone decided to put this to the test by removing the fan and heatsink entirely. The results were surprising, to say the least.
http://www.tomshardware.com/cpu/01q3/010917/index.html
4) App o’ the week
With the advent of Microsoft Windows 2000 brings easier access to thin clients through the use of Microsoft’s RDP protocol. Access a Win2K desktop from DOS, any version of windows, and now, Linux. Nope, it’s not supported by Microsoft, but finally you can connect to a Terminal Server to get at those corporate apps from your Linux box.
http://www.rdesktop.org
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