This week I upgraded the guts in my desktop. For the video card I jumped up to an ASUS EN9600GT silent graphics card. It is pretty “bleeding edge” as far as Linux goes, and it is a double-wide card with a massive heatsink where others would have a fan. I like to reduce the white noise.
Unfortunately, it is too new for the currently-supported Ubuntu drivers. I used Ubuntu’s NvidiaManual docs to manually upgrade to the 173.14.12 drivers from NVidia’s site, and then things were happier. Except video playback. Files and DVDs seem to work okay, but the colors are off, notably, people get rendered with blue or purple flesh. (more…)
The other day I was working on a shell script to be run on several hundred machines at the same time. Since the script was going to download a file from a central server, and I did not want to overwhelm the central server with hundreds of simultaneous requests, I decided that I wanted to add a random wait time. But how do you conjure a random number within a specific range in a shell script?
Updated: Due to much feedback, I now know of three ways to do this . . .
1) On BSD systems, you can use jot(1): sleep `jot -r 1 1 900`
2) If you are scripting with bash, you can use $RANDOM: sleep `echo $RANDOM%900 | bc`
3) For portability, you can resort to my first solution: # Sleep up to fifteen minutes
sleep `echo $$%900 | bc`
$$ is the process ID (PID), or “random seed” which on most systems is a value between 1 and 65,535. Fifteen minutes is 900 seconds. % is modulo, which is like division but it gives you the remainder. Thus, $$ % 900 will give you a result between 0 and 899. With bash, $RANDOM provides the same utility, except it is a different value whenever you reference it.
Updated yet again . . . says a friend:
nah it’s using `echo .. | bc` that bugs me, 2 fork+execs, let your shell do the math, it knows how
so $(( $$ % 900 )) should work in bsd sh
For efficiency, you could rewrite the latter two solutions:
2.1) sleep $(( $RANDOM % 900 ))
3.1) sleep $(( $$ % 900 ))
The revised solution will work in sh-derived shells: sh, bash, ksh. My original “portable” solution will also work if you’re scripting in csh or tcsh.
I wanted to know what time it was in UTC, but I forgot my local offset. (It changes twice a year!) I figured I could look in the date man page, but I came up with an “easier” solution. Simply fudge the time zone and then ask.
0-20:57 djh@noneedto ~$ env TZ=UTC date
Tue May 6 03:57:07 UTC 2008
The env bit is not needed in bash, but it makes tcsh happy.
0-11:17 djh@ratchet ~> cd public_html/toldme
0-11:17 djh@ratchet ~/public_html/toldme> svn sw http://svn.automattic.com/wordpress/tags/2.5.1/
[ . . . ]
Updated to revision 7839.
When I logged in to post this little note, it blocked me and ran the upgrade procedure, then I had to log in again, and here I am!
There’s a further note about the secret key setting:
Since 2.5 your wp-config.php file allows a new constant called SECRET_KEY which basically is meant to introduce a little permanent randomness into the cryptographic functions used for cookies in WordPress. You can visit this link we set up to get a unique secret key for your config file. (It’s unique and random on every page load.) Having this line in your config file helps secure your blog.
It leaves me to wonder: if the secret key can be randomly generated by a machine, why not go ahead and do that and then stash it in the database? There may be a good reason for that . . .
In unrelated news, I upgraded to the newer Ubuntu release at home yesterday. The only trick I have noticed so far is that it runs with Firefox 3.0, which is beta, and I lost use of my foxmarks plugin, for now. So, I’m waiting until that is supported before I upgrade my workstation.
I had a rough go of it until I found BlackNight’s post, and now my Canon i250 printer works with Ubuntu like a charm. I thought I would recap here for those who, like me, at first Googled in vain. If you paste these command into Ubuntu 7.10 (Feisty) things ought to work:
First, enter your sudo password:
sudo echo
Now, this paste just might set up everything you need:
If things turn out less-than-straightforward, definitely review BlackNight’s page for details, and if this does work out for you drop him a thank you note in the comments!
I have been playing with Google Trends, which will be happy to generate a pretty graph of keyword frequency over time. A rough gauge to the relative popularity of various things. This evening, I was riffing off a post from the Royal Pingdom, regarding the relative popularity of Ubuntu and Vista, among other things.
This is just a note which I contributed to a thread on sage-members, to get something off my chest, as to where people should maintain their crontab entries. I sincerely doubt that reading what I have to say will bring you any great illumination.
I’d say, any reasonable SysAdmin should default to /etc/crontab because every other reasonable SysAdmin already knows where it is. If anything is used in addition to /etc/crontab, leave a note in /etc/crontab advising the new guy who just got paged at 3:45am where else to look for crons.
For production systems, I strongly object to the use of per-user crontabs. I’m glad to hear I’m not alone. One thing I have to do in a new environment tends to be to write a script that will sniff out all the cron entries.
And then there was the shop that used /etc/crontab, user crons, and fcron to keep crons from running over each other. This frustrated me enough that I did a poor job of explaining that job concurrency could easily be ensured by executing a command through (something like) the lockf utility, instead of adding a new layer of system complexity.
For production systems, I think it is best to use a single, centralized /etc/crontab, which simplifies the job of tracking batch processes. On a production system, batch scripts should be sufficiently robust such that if they are resource or lock-intensive, they make sure everything is okay before they get to work. Stuff like user crons and fcrontab can live in your development and corporate servers.
Of course, sometimes you inherit production systems with people who don’t think like you do. You’ll need to review what random user crons are running on each system. With any luck you’ll have a sane OS that keeps the user crontabs in a well-documented location. (FreeBSD? /var/cron/tabs . . . SuSE . . . still not sure . . .) Of course, luck is a fickle mistress, and sometimes you have to do it the evil way:
> cat /etc/passwd | awk -F : '{print "echo crontabs for user "$1"\ncrontab -l -u "$1"\n"}' > /tmp/crontabs.sh
> head /tmp/crontabs.sh
echo crontabs for user root
crontab -l -u root
echo crontabs for user bin
crontab -l -u bin
echo crontabs for user daemon
crontab -l -u daemon
echo crontabs for user lp
> sudo sh /tmp/crontabs.sh | mail -s "`hostname` crontabs" $USER
If you are borrowing my “recipe” you will likely want to put your e-mail address where it says $USER . . . and, you may have to do the same for fcron as well. Bah!
cat /etc/passwd | awk -F : '{print "echo fcrontabs for user "$1"\n/usr/local/bin/fcrontab -l -u "$1"\n"}' > /tmp/fcrontabs.sh
sudo sh /tmp/fcrontabs.sh | mail -s "`hostname` fcrontabs" $USER
Scenario: a Linux system with two drives. The system was built with resiliency as a priority, but availability is not critical. So, the filesystems were mounted atop md raid1 for resiliency, and the swap was striped across an md raid0 for performance.
One disk failed and was removed from the system. System returns to service on remaining drive until RMA is completed. Users are informed that the system is available but does not have swap space. Consensus is reached to add some temporary swap space via a swapfile. (more…)
So, I’m setting up a box. I need to test different filesystem configurations, which will involve a lot of boot-configure-install-post-install-benchmark cycles. We have a nice network boot infrastructure, but getting serial booting to work is always fun. Today I found that the vendor has set up BIOS “remote access” to COM2. Funny thing, the box only has one serial port! So, I set that to COM1, and configure console redirection only up to the boot loader, tell the bootloader that I want text console=ttyS0 and we’re in business!
But man, if SuSE’s YaST aint a bloody mess when it downgrades to text on a serial port:
What you don’t see here is the constant slow screen-redraw, constant pressing control-L. This is what it looks like at a good moment!
I think I understand why. I mean, I would think that Linux developers would take serial consoles and text mode to heart. After all, that’s the whole point, right? But that’s how I think, because I manage dozens of servers at a time, remote, and all my boxes are rack-mount jobbies with lots o’ fans and nobody wants to be in the same room.
But the developers who hack on Linux probably aren’t hard-core SysAdmins. Their dev system is some beat-up old hardware sitting near their desk, wired up to a spare VGA monitor, so yeah, text mode is kind of an afterthought. Especially given the pain in the butt that setting up serial consoles can be!
dman: Anyone ever been on a Unix box and see uptime reset without a reboot? SmooveB: dman: yes David: dman: yes ***dman smiles David: dman: my personal favorate is the rollover or the negative rollover SmooveB: dman: linux in particular dman: LINUX, you say? David: SmooveB: fancy that, that’s where I’ve seen it too
It seems that this issue is near and dear to those involved in “the uptime project” where, I guess, geeks sit around comparing uptime size. Which is kind of juvenile. However, this bug gave me a hearty laugh:
How reproducible:
ALWAYS
Steps to Reproduce:
1. Boot Linux system
2. Go away for 497 days
3. check uptime
Ahhh, so in my getting to grips with, I have a few gripes about Linux. Some day I may cultivate these into a well-formed, coherent technical explanation, but just now . . . just now, I’ll share with you a special favorite rant of mine.
New install, right? By default, it wants to check the install media (who cares?) then there’s a screen that says “welcome to <version of Red Hat>” where you get the chance to say “ohhh, wrong CD …” then you move on to disk partitioning, and you have to intentionally select that yes you want to erase all data, and enter a bunch of other parameters … network … firewall, SE-Linux … altogether 10-15 minutes if you know what you are doing. Nothing onerous. Lots of “yes, a firewall, and these other things, these are all a good ideas, I’ll just mostly agree to what you suggest.” (more…)
I’m new to Linux, but I’m trying out Fedora Core 4 on my work laptop. It’s pretty slick once you change the desktop environment to KDE. But I want to be able to play mp3s, and there’s nothing in the default system that can handle this, and yum doesn’t know where to find good stuff like mplayer or mpg123. (Yeah, I’m a command-line type of guy . . .)
So, I go shopping for “repositories” that extend the Fedora Core base repository . . . and the short answer is that if you do this:(more…)
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