2001 05 17

                    LINUX NEWS
             Thursday, May 17, 2001
       Read By 6,000 Linux Enthusiasts Weekly!


1) Sean’s Notes

2) Linux News

IPv6 News
Linux at the Top of TPC Benchmark
Nokia Media Terminal to use Loki Games
Erase the Eazel

3) Linux Resources

To Port, or Emulate, that is the Question
Core Files, and What to do with 'em
A Comparison of Linux PDAs
Dealing With setuid Programs
Protect Your Network

4) App o’ the week

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1) Sean's Notes
The ability to run a certain program at a certain time is
critical to the stability of a system.  You may want to run
backups at midnight, clean up temporary files that haven't
been touched in weeks, or run some reports.  Since you've
probably got better things to do than look at your watch all
the time, you might want to automate this.

cron is the daemon that handles this task.  With it, users
have the ability to schedule commands to run at regular
intervals, be it daily, weekly, or even every minute.

The standard way to schedule a job is to edit your crontab,
or the list of cron jobs you wish to run, via

crontab -e

That will bring you into the editor of choice, specified by
the $EDITOR environment variable.  Each line in this file
specifies one job.  There are 6 fields you'll have to know

minute hour day month weekday command

A \* means anything goes.  So, to run something at midnight
every day:

0 0 \* \* \* command

Or, Midnight on Sunday

0 0 \* \* 0 command      or,
0 0 \* \* Sun command

(note that with day of week, and month, you can use the
names instead of numbers.  0 is Sunday, 1 is Monday, etc)

You can also specify ranges.  Here is weekdays, on the half

0,30 \* \* \* 1-5 command

Once you exit the editor, the job will be scheduled.  It
will exist and run until you delete it or comment it out
from "crontab -e".

"command" can be any Unix command.  Usually, you'll put the
complex ones into a script and run that.  Keep in mind that
this script will be run as the user that you ran the crontab
command from, so make sure the permissions are such that
other people can't edit the script.

If your command produces any output, it will be mailed to
the owner of the crontab.  You can change who it goes to
(i.e. for root's crontab) by putting


in the top of the crontab.  You may also want to add


to force the Bourne shell to be used.  Normally, scripts
may output debugging information, so you may want to
redirect the output to /dev/null:

command > /dev/null

Any errors will not be caught by that, and will get emailed
by the process above.  If you still don't want to hear them,
direct both errors and regular messages to /dev/null

command > /dev/null 2>&1

Some examples of regular jobs you may do:

# Process web logs with webalizer (www.webalizer.org) at
0 0 \* \* \* (cd /var/www/html/stats && /usr/local/bin/webalizer
/var/www/logs/access_log) > /dev/null

# Process system logs with logcheck (www.psionic.com)
0 \* \* \* \* /usr/local/etc/logcheck.sh

Executing "crontab -l" is a quick way to see your crontab
without having to bring it into an editor.

root can edit/list other people's crontabs:

crontab -e -u fred

"man 5 crontab" is another great reference for some more
ways to use cron.

As you can see, cron is a powerful tool.  When using it, you
have to keep a few things in mind:

- The program should run without requiring any input

- Your path is likely different than your regular shell
  Always specify locations of commands explicitly

- Try to run commands with the least privilege necessary,
  i.e. you don't always need to use root's crontab

Long live the Penguin,


Visit the Linux News Board at

2) Linux News

IPv6 News
The current Internet Protocol, version 4, has shown some
limitations in terms of keeping up with growth.  IPv6 is the
protocol destined to replace it. This article gives a good
background on the reasons we're not running v6 now, and what
has to happen.


Linux at the Top of TPC Benchmark
The TPC-H benchmark is a measure of how well a database
performs in a decision support situation. Vendors like to
tout their TPC numbers. Well, Linux 2.4.3 now tops the 100GB
category, running on an SGI system and IBM's DB2.


Nokia Media Terminal to use Loki Games
"The Media Terminal is an innovative infotainment device
that seamlessly combines digital video broadcast (DVB),
gaming, full Internet access, and personal video recorder
(PVR) technology. As part of the agreement Linux-based
games from Loki will be pre-installed on the Media Terminal.
Anticipated roll out of the Media Terminal will be early
Fall in Europe."


Erase the Eazel
It's official...Eazel, the makers of Nautilus, are shutting
down. However, we're promised that development will be picked
up by others in the GNOME community. I like the product, but
not the resources it takes on my system. I can only hope that
the work will continue.


3) Linux Resources

To Port, or Emulate, that is the Question
In order to get a Windows game to run on Linux, you would
either have to port the game to native X/Linux code, or
build an abstraction layer to emulate the Windows API. The
former is being done successfully by Loki software, and the
latter by the up and coming Transgaming. Which is better?


Core Files, and What to do with 'em
So you see a large file called "core". What is it?  Where
did it come from? They can be all over your filesystem,
eating up space, so you'd better learn how to deal with them!


A Comparison of Linux PDAs
I've got a Palm Pilot, and I'd sure be lost without it. As
demand for applications on these devices grows, the open
nature and low profile of Linux makes a great fit! This
review covers the Agenda VR3, Compaq iPaq, and the G. Mate


Dealing With setuid Programs
The setuid attribute on files indicates that it can assume
the UID of the owner when it's run, rather than that of the
current user. This has serious implications, especially when
root is the owner! Learn how to deal with setuid files, and
clean them up.


Protect Your Network
Firewalls are an essential part of security, but they're
only a small part of your total security solution. This
article has some pointers on what else to look for, some
audit techniques, and plain old good advice.


4) App o' the week
The Abacus Intrusion Prevention System is a set of utilities
designed to increase the security of your system. Logcheck
will process your log files and email you of any anomolies
or security breaches. PortSentry monitors for portscans, and
can react by blocking the offender if you wish. HostSentry
learns the login patterns of your users and notifies you of
anything unusual.


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