June 5, 2008

Ask Linux.com: Unix basics, old school network sniffing, and router madness

Author: Linux.com Staff

In recent postings on the Linux.com forums, readers ask questions about transitioning from Windows to the Unix-like approach of the shell, the Linux filesystem, and managing hard disks. Plus, we have brainteasers of the unanswered question variety -- this time, testing your knowledge of routers and boot sequences.

Getting used to Linux conventions

In the New to Linux forum, three users asked questions that trace back to Linux's Unix heritage.

Windows system administrator QueenB asked for help installing an application from the bash shell on a virtual Linux server -- the install was failing, and she wanted more detail on how to string commands together, since the rules obviously were not the same as those of Windows's command line. Penguin debugged the error in QueenB's shell commands -- an unnecessary wild card character -- and provided some shell basics.

Kell asked about the contents of the various directories created as mount points by his installer. "On my Linux setup I see a partition for swap, boot, and usr. Is the boot partition where all of the Linux OS is stored? When additional programs are installed, are they to be installed in the boot partition? Is this the correct location? What is the usr directory for ... data?" User tophandcwby responded with a link to documentation explaining the Linux filesystem hierarchy.

And reader jkcrowley discovered that only 5% of his hard drive remained unused, and asked what he could do to reclaim some disk space. Anthony Robbins and proopnarine explained how to use df and find to figure out what partitions and files were consuming more than their fair share of space, and the virtues of keeping /, /var, and /home in different partitions.

All three exchanges illustrate that even those with some experience using the command line and disk partitions on Windows or other platforms may still have questions when they move to Linux for the first time.

Packet sniffing and the modern modem

But transitioning to Unix conventions wasn't the only topic of discussion. User Warp2063 is trying to reverse engineer the communication protocol of an old game system that connects over analog modem lines. He had a Linux box connected to the same phone line as one of the consoles, but could not find an appropriate application to sniff the packets.

Reader Penguin recommended the general-purpose packet sniffer Wireshark. By selecting the modem line as the interface to monitor, he said, Wireshark could log all of the relevant traffic to file, just as it can for an Ethernet connection.

You know 'em, you love 'em, you can't live without 'em: unanswered questions

Want to start June on a high note? Try your luck at deciphering these unanswered questions.

First, boot-time hijinks. OrangePill has an Ubuntu 8.04 machine vying hard for the title of longest boot time in captivity: on the order of half an hour. Several readers have suggested likely culprits, including swap space and a corrupted install, but no far none of the candidates has proven correct.

Finally, Sathya has a challenge for all of you networking experts. He is putting together a local network with three routers running GNU Zebra, and cannot get the routers to pass routing updates to one another. If you know that LSA stands for link state advertisement without having to look it up, Sathya would appreciate your help figuring out his router conundrum.

That's all for now. Remember, ask and answer questions in the forums, not in the comments attached to this article, and don't forget to brush up on the forum posting guidelines to ensure a better visit for everyone.


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