2001 05 24

                    LINUX NEWS
             Thursday, May 24, 2001
       Read By 6,000 Linux Enthusiasts Weekly!


1) Sean’s Notes

2) Linux News

Mind Rover to be Released
Watch out for the Cheese Worm
Browser Plugins for Linux
1.7GHz Xeon

3) Linux Resources

A Path To Knowledge
Bandwith Limiting
Win a Free Tape Drive
The Linus Autobiography
RIP: Linux on the Desktop

4) App o’ the week

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1) Sean's Notes
Last week I explored the basic use of the crontab daemon,
which is the facility that enables you to schedule the
regular execution of scripts:


A sharp reader pointed out that the option to edit your
crontab (-e) sits right next to the option to remove the
crontab (-r).  His suggestion was to back up your crontab

crontab -l > ~/.crontab.bak

...and to replace from the backup:

crontab ~/.crontab.bak

Note that specifying a filename on the commandline *replaces*
your crontab with the given file, it does not add.

Using the crontab command is not the only way to schedule
jobs through cron.  The version that ships with most Linux
distributions, written by Paul Vixie, creates two additional
methods.  One is the /etc/crontab file, the other is
/etc/cron.d.  The first is much like the root crontab file,
though it can be edited directly.  The second can contain
multiple files, each consisting of similar crontab entries.
The difference is that these entries have seven columns
instead of the regular six.  Column six specifies the
username to run under.

For example, you could create /etc/cron.d/backup:

0 0 \* \* \* amanda /usr/local/sbin/amdump DailySet1

Storing individual application crontabs makes things a lot
easier for package maintainers, and sysadmins trying to
figure out what commands are necessary to keep various
applications happy.  I tend to prefer this method (and the
next) because it keeps me from having scripts all over the

If you look at your default /etc/crontab, you'll see some
lines in there:

01 \* \* \* \* root run-parts /etc/cron.hourly
02 4 \* \* \* root run-parts /etc/cron.daily
22 4 \* \* 0 root run-parts /etc/cron.weekly
42 4 1 \* \* root run-parts /etc/cron.monthly

These lines simply schedule a command to run hourly, daily,
weekly, and monthly.  These jobs make creating cron jobs a
lot easier. Want to run a script every hour?  Toss it in
/etc/cron.hourly.  There's no messing with crontabs, as the
script stays separate from all the other crontabs, so you
always know what it is a part of.  The run-parts command is
also a handy one for scripting.  It takes a given directory
and runs each file inside in turn.  If you're concerned about
spreading out your hourly cron jobs so that they all don't
run right on the hour, this method is great because it
ensures that only one is running at a time.

Scheduling jobs is very powerful, but could cause some
problems if misused.  Think of a user running a web
statistics program every minute...that could certainly cause
some problems!  Enter /etc/cron.allow and /etc/cron.deny.

If you want to allow only certain users to use crontab,
enter their usernames in /etc/cron.allow.  Anyone who isn't
in the list who tries to edit their crontab will get a
message like:

$ crontab -e
You (sean) are not allowed to use this program (crontab)
See crontab(1) for more information

If you want to make sure certain users can't use it, put
them in /etc/cron.deny.  Cron is finicky, so make sure you
only use one of these files at a time, and if it ends up
being empty, delete it.

So that wraps up my two part series on cron.  Hope you found
it useful!

Long live the Penguin,


Visit the Linux News Board at

2) Linux News

Mind Rover to be Released
Loki Games, the porters of Windows games to Linux, announced
the release of Mindrover:

"By day, you're a researcher on Jupiter's moon Europa. In
your free time you re-program the rovers to race around the
hallways, battle it out with mini-lasers and rocket
launchers, and find their way through mazes."

Looks pretty cool, and there is a demo available.


Watch out for the Cheese Worm
If you remember the L10n worm from a few months ago, we've
got a new one called the "Cheese Worm". This one isn't too
bad, as far as worms go: once it gets into your system, it
tries to erase the back doors that L10n left behind.


Browser Plugins for Linux
"Looking to narrow the gap in features between Windows- and
Linux-based platforms, CodeWeavers Inc. has developed a
series of browser plug-ins such as Shockwave and QuickTime
for Linux-based Internet appliances."


1.7GHz Xeon
Anandtech is starting to become a favourite site of mine
because of its detailed analysis of hardware. In this
installment, they look at the new Xeon chip, especially the
differences between it and it's older siblings.


3) Linux Resources

A Path To Knowledge
This article takes a slightly humourous look at the path to
Unix Wizardry. It's a dialogue between a wizard and a newbie,
where the wizard explains the journey.


Bandwith Limiting
Like many routers, Linux can do complicated queuing of
packets in order to prioritize traffic down a congested link,
or to limit the amount of bandwidth that one application can
take up. This recently posted HOWTO shows the various ways
this can be implemented.


Win a Free Tape Drive
This company gives away several tape drives each month. When
I entered myself, I noticed that they have a Linux page
claiming that they are Linux-compatible. It's always good to
see companies noticing the Linux market!


The Linus Autobiography
"Just for Fun: The Story of an Accidental Revolutionary" is
the autobiography of Linus Torvalds, the creator of Linux.
Linux.com has managed to get Chapter One placed online.
It's well worth a read!


RIP: Linux on the Desktop
Last week I mentioned the demise of Eazel, a company
looking to revolutionize the Linux desktop. An opinion on
Linuxplanet.com says that this is a sign of the end for
desktop Linux itself. Is this a bad thing, he asks? We do
well on the server end, shouldn't that be enough?


4) App o' the week
If you've ever had some serious filesystem corruption, you
know that fsck can get you back on your feet, but the results
aren't always pretty. This week's utility is designed to take
a very damaged filesystem, and get the drive to the state
where you can mount it read only to recover the data.

Contrast this to fsck, which will get you a filesystem that
works, but with a lot of data lost in the process. The author
claims that his program, e2salvage, can deal with much more
damage than can fsck. Let's hope it never comes to it, but
keep this one in your rescue kit.


(C) 2001 BrainBuzz.com. All Rights Reserved.


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