LINUX NEWS
RESOURCES & LINKS FROM BRAINBUZZ.COM
Thursday, May 17, 2001
Read By 6,000 Linux Enthusiasts Weekly!TABLE OF CONTENTS
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 Eazel3) 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 Network4) 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 about:
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 hour:
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
MAILTO=fred
in the top of the crontab. You may also want to add
SHELL=/bin/sh
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
midnight 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,
Sean mailto:swalberg@brainbuzz.com
Visit the Linux News Board at http://boards.brainbuzz.com/boards/vbt.asp?b2
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.
http://www.ecompany.com/articles/web/0%2c1653%2c11667%2c00.html
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.
http://www.tpc.org/tpch/results/h-ttperf.idc
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.”
http://www.lokigames.com./press/archive.php3?05162001
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.
http://mail.gnome.org/archives/gnome-hackers/2001-May/msg00203.html
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?
http://www.gamespy.com/articles/may01/wine/
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!
http://www.linuxnewbie.org/nhf/intel/filesys/corefiles.html
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 Yopy.
http://linux.oreillynet.com/pub/a/linux/2001/05/11/linux_pdas_one.h tml
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.
http://linux.com/enhance/newsitem.phtml?sid=1&aid286
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.
http://www.nwfusion.com/net.worker/research/2001/0514feat2.html
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.
http://psionic.com/abacus
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