LINUX NEWS
RESOURCES & LINKS FROM BRAINBUZZ.COM
Thursday, May 24, 2001
Read By 6,000 Linux Enthusiasts Weekly!TABLE OF CONTENTS
1) Sean’s Notes
2) Linux News
Mind Rover to be Released
Watch out for the Cheese Worm
Browser Plugins for Linux
1.7GHz Xeon3) Linux Resources
A Path To Knowledge
Bandwith Limiting
Win a Free Tape Drive
The Linus Autobiography
RIP: Linux on the Desktop4) 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:
http://www.ertw.com/~sean/newsletter/May+17%2C+2001
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 periodically:
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 filesystem.
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,
Sean mailto:swalberg@brainbuzz.com
Visit the Linux News Board at http://boards.brainbuzz.com/boards/vbt.asp?b2
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.
http://www.lokigames.com/products/mindrover/
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.
http://news.cnet.com/news/0-1003-200-5949401.html
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.”
http://www.eet.com/story/OEG20010508S0061
-
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.
http://www.anandtech.com/showdoc.html?i72
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.
http://www.rootprompt.org/article.php3?article#77
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.
http://www.ibiblio.org/pub/linux/docs/howto/Bandwidth-Limiting-HOWT O
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!
http://www.ecrix.com/extreme/index.cfm?idnner&reff095
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!
http://www.linux.org/people/justforfun.html
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?
http://www.linuxplanet.com/linuxplanet/opinions/3387/1/
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.
http://project.terminus.sk/e2salvage/
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