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I discuss netstat -r (which shows you which route the UNIX host thinks packets should take through the network) as well as traceroute in Hour 14, “Router and Switch Basics.” The traceroute command is a great way to find the routers that a packet needs to go through in order to get from point A to point B. The thing to know about it under UNIX is that not all implementations of UNIX have it. Most do, but there are still one or two proprietary implementations of UNIX that do not. However, you can always get it from ftp://ftp.ee.lbl.gov/traceroute.tar.Z. You’ll need to be reasonably comfortable with the UNIX command line to use this, because it comes in source code form—it requires you to use the tar command to extract the source code and the make command to compile it.
UNIX hosts are typically reliable servers used to house databases, client/server applications, and Telnet sessions. They’re also awesome for running Web and FTP servers.
Most UNIX services run through background programs called daemons. Some service problems can be solved by stopping and starting a daemon process.
Many times, you’ll need to run commands as the root user. To get comfortable and become good at this, you’ll probably want to set up a play system, where you’re able to learn from your mistakes without affecting a crucial system.
You can keep track of the services and clients running on your system through the netstat -a command. A busy UNIX system can have hundreds or thousands of sockets open at any given time; you can track down the socket you’re looking for by using netstat in conjunction with the grep command.
Ping is your best friend (as usual with TCP/IP troubleshooting) in determining whether a problem lies with the UNIX server, the network, or the router.
Q I can’t get to a file on my G: drive (it’s mapped to my UNIX server’s /home file system), but the person next to me can. When I log in as her, I can get to the file. What’s up with this?
A UNIX security and file permissions is a reasonably large topic, and I touch on it in Hour 18. To answer your question, though, it’s likely that the file or directory belongs to a group that you do not belong to. Look at the group on the file using ls -la and add yourself to that group.
Q We’ve recently gotten a new Internet Service Provider, and all of our IP numbers have changed. Now, every time I boot my UNIX system, I get “NFS Server Belboz not responding.” What’s going on?
A It’s likely that the Belboz system is only listed in the /etc/hosts file of the UNIX system. View the file, and you’ll likely see that the TCP/IP number is wrong; change it to the new number.
Q I hear that UNIX is less secure than other operating systems. True?
A No. UNIX’s problem is that it is more configurable than other operating systems, which means that sometimes it’s misconfigured and is therefore less secure. Also, the level of knowledge about the internals of UNIX is pretty high—source code is available for some implementations, which allows hackers to probe for security holes in programs. Actually, even though Windows NT doesn’t have source code publicly available, holes have been found in programs there. Just like any operating system, UNIX has several problematic, widespread server programs—such as sendmail—that have caused widespread publicity and security panics, but these have always been patched rather quickly.
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