Local "howto" information

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This page contains "howto" information for random bits of hardware and software. Some of it is general, but much is very specific to my configuration, so it may break for yours; use caution when trying any of this stuff.

Table of contents

• Automatic clock setting from an NTP time server
• Burning DVDs and CDs

Contents of this page:

1. Local "howto" information
   1. Table of contents
      1. Terminology
   2. Networking
      1. Ethernet
      2. General IP networking
      3. DNS tricks using perl
   3. Linux guts
      1. Server logs
      2. Memory management
      3. rpm
   4. Hardware
      1. Zip drive
      2. Floppy disk

• Hard drive means just that, though I have a tendency to say "disk" instead. Back when I was introduced to magnetic storage, floppies were quite new, so "disk" without qualification always meant a rigid disk. (Probably one with removable media; you don't see those anymore, because they can't be made very dense, only up to a few hundred megabytes. Tiny by modern standards.)
• Disk therefore means floppy disk or (rarely) zip disk.
• DVD covers the fourth kind of disk, which also includes CDs.

Networking

See my Ethernet Cheat Sheet for Ethernet pinouts and wire color code conventions. (This is on a page of its own for easy printing.)

• The /etc/services file has the protocol/port to service name mapping.
• "netstat -t" reports on open TCP connections.
• Use "cat /proc/net/dev" to get a tabular version of interface statistics.

    rgr> perl -e 'use Socket; $iaddr = inet_aton("128.197.54.20"); print join(" ", gethostbyaddr($iaddr, AF_INET)), "\n";'
    darwin.bu.edu  2 4 \200\3056^T
    rgr> 

    % nslookup -q=PTR 20.54.197.128.in-addr.arpa | perl -ne 'print "$1\n" if /in-addr.arpa\s+name = (.*)$/;'
    darwin.bu.edu.
    % 

Linux guts

Hardware

See also the Burning DVDs and CDs page (which is about hardware that is not so obsolete).

Mounting:

Use "mount /mnt/zip". If this fails with an error message that looks like this

       mount: the kernel does not recognize /dev/sda4 as a block device
              (maybe `insmod driver'?)

then this is probably because the machine was booted with the Zip drive off. If that's the case, then

       modprobe imm

will probably be sufficient to get /dev/sda4 recognized, after which the drive can be power cycled without needing to repeat the modprobe. (The boot-time modprobe is done in the /etc/rc.d/rc.modules script. -- rgr, 28-Dec-99.)

If /var/log/messages says

       modprobe: can't locate module block-major-8

and lsmod shows imm already loaded, then do

       rmmod imm; modprobe imm

to force reloading. -- rgr, 2-Jul-00.

Unmounting:

"umount /mnt/zip", and then hit the button to eject. Doing "eject /mnt/zip" seems to work, but only for root.

Formatting:

mke2fs /dev/sda4

You can add the "-c" option to check for bad blocks, but I haven't found a bad block yet, and this is what takes most of the time (about 4.5 minutes), as it has to read the entire drive. (My guess is that bad blocks are detected and "repaired" by the drive, so it's no surprise that I never found one. -- rgr, 7-Aug-01.)

Checking for bad blocks:

When doing badblocks on Zip, use 98288 for number of blocks -- this is (- (/ (* 2048 96) 2) 16), for 96 cyl, 2048 blocks/cyl, 0.5k/block, minus some magic factor. If there is some reason to suspect the existence of a bad block, one can also use the "-c" option to e2fsck when checking disk integrity (but see the comment under "Formatting" above).

Checking file system integrity:

Periodically, when mounting Zip disks, the following warning will appear in /var/log/messages:

       EXT2-fs warning: maximal mount count reached, running e2fsck is recommended

To address this, before mounting the disk, do

       e2fsck -f /dev/sda4

The "-f" option will "Force checking even if the file system seems clean" (from the man page); without it, e2fsck does a quick check, so "-f" is more thorough. You can also add the "-c" option to request bad block checking (but see the comment under "Formatting" above).

Erasing:

To erase a Zip disk thoroughly (or any other disk device or partition for that matter), you can do a "write" test to check for bad blocks:

       badblocks -w /dev/sda4 98288

This takes a while, as it writes a number of patterns across the whole disk, and then rereads them. Each read/write pass takes about nine minutes; the whole process is more than half an hour.

[Note that the shred program does this exactly this job, but more thorougly. -- rgr, 7-Feb-21.]

Note the existence of the mzip command.

[The "Zip drive backup" section that was here has been renamed and given its own page. -- rgr, 7-Aug-01.]