The Cron of Tab

Damn, setting up crons was supposed to be a walk in the park, so much so that I didn’t even budget mental energy for it! Maybe that was the problem…

Anyways, lessons learned from setting up simple cron jobs.

1. How-Tos are good, but man is better.
2. crontab -e will either load your current crontab, or load a blank template for you.
3. crontab -r will kill your current crontab. Which is why it’s nice to keep the output of crontab -l, which lists your crontab jobs, in a backup file. Because unless you like setting up crons, you don’t want to be left high and dry without a backup.
4. try running your jobs before putting them in the crontab. Or, if you’re like me, do crontab -l, cut and paste, and figure out why /usr/local/binruby is not the command you want (/usr/local/bin/ruby was what I was looking for).
5. to make sure your jobs are running, tail -f /var/log/syslog. Note that this doesn’t tell you if they’re crap or not.
6. Or, append your output to a log, and check to see that the log is growing.

I’m still kind of cruxing about how I’m going to run this on a deployed app. I think I’m going to have to get ops to add deploy_user, and add the crons on deploy_user’s behalf. Of course, I’ll worry about that when I can actually smoothly install mod_rails on my semi jacked up box. I must be the only tard in the universe who screwed up a mod_rails install, but more on that tomorrow.

Tomorrow (er, 1 week later)

In the mad rush to launch (more later), I forgot to update this page, which is bad because this is my scratchpad that has more than once saved me from repeating a painful process. Summary: anyone installing mod rails should take 4 minutes and view the railscast. I was missing the following in my conf file:


LoadModule passenger_module /usr/local/lib/ruby/gems/1.8/gems/passenger-1.0.5/ext/apache2/mod_passenger.so
RailsSpawnServer /usr/local/lib/ruby/gems/1.8/gems/passenger-1.0.5/bin/passenger-spawn-server
RailsRuby /usr/local/bin/ruby


Metrics Part IV: RRDTool on Ubuntu 7.04 (Feisty)

The production instance of this metrics server is going to run on Ubuntu Feisty, which comes installed with rrdtool 1.2, but the ruby bindings I want (need) to use bind to 1.3. So this is how to install rrdtool on Feisty.

(1) download the source:

curl http://oss.oetiker.ch/rrdtool/pub/rrdtool.tar.gz > rrdtool.tar.gz

then follow the instructions rrdbuild page : basically,

./configure

sudo make

sudo make install

However, in order to get configure to complete, I needed to install a couple of dependencies, pango and xml-2. I like configure, it’s very good about telling you what is missing and where to get it. And the rrdbuild page is also great at specifying exactly how to install the missing packages.

I figured I was up and running at that point. I built the ruby bindings from {src dir}/bindings/ruby, but when I tried to run the files I had been running on my Mac, I got:

/usr/local/lib/ruby/site_ruby/1.8/x86_64-linux/RRD.so: librrd.so.4: cannot open shared object file: No such file or directory - /usr/local/lib/ruby/site_ruby/1.8/x86_64-linux/RRD.so (LoadError)


NOT COOL.

How can a file that exists, /usr/local/lib/ruby/site_ruby/1.8/x86_64-linux/RRD.so, not be found? Was it a permissions thing? I tried building as sudo, same thing. Then I made sure that the file actually existed, just to check my head. Yes, it’s there. Yes, I’m getting the same error. Wait. Could it be the librrd.so ? I try a

ldconfig -v | grep rrd

and only get librrd.so.2. Hmmm. OK, desperate times…I edit /etc/ld.so.conf.d/local-installs.conf, and add

/usr/local/rrdtool-1.3.0/lib


to the path. That worked. The ops team is not going to be super thrilled about the amount of jackassery it took to get this up and running, which is why I’m documenting it here. Because they’ll make me maintain it. Just like I would if I were in their shoes