Yesterday I wrote that Apple has changed the way they do the periodic maintenance jobs on Mac OS X. I spent some time last night figuring out how it's being done now. Here's what's happening.
The way most Unix systems have done the periodic maintenance from time immemorial is to schedule them as cron jobs. The cron daemon on a Unix system is a program that runs quietly in the background-- that's why it's called a daemon--keeping track of a list of commands and times at which to run those commands. Each user can have a table of scheduled jobs, called a crontab. The mother of all crontabs is the system crontab, that's owned by the operating system itself. The system crontab listed the times to run the scripts called daily, weekly and monthly, to do periodic maintenance. The scripts are still there in the latest versions of Mac OS X. You just have to look in the /etc directory. The scripts are still there, but they are not used. To tell you what's being done now, I must go off on a tangent. Unix systems have had a very confusing way of starting things up when they are booted. Some things are launched by one set of scripts and another set of things are launched by another method entirely. (Linux users should think of rc.d and xinetd.) Apple wanted to clean this up, so they invented a new traffic cop that's the very first program launched by the kernel and called it launchd. (The "d" on the end is a clue that launchd is also a daemon.) All the startup stuff is handled in one place by launchd. Most of the functionality of crond was rolled into launchd, so Apple has turned off cron in Tiger. The new launchd periodically calls a program called periodic to handle the rest of the stuff crond used to do. The periodic program has its own cleanup scripts in the directory /etc/periodic/daily, / etc/periodic/monthly and /etc/periodic/weekly. (The /etc directory is invisible in the Finder because Apple is trying to hide the geeky Unix stuff from the proletariat.) As of version 1.3, MacJanitor calls the periodic program instead of the old crond scripts, so it should be safe to use it. (I have not tried it.) -------------- next part -------------- A non-text attachment was scrubbed... Name: smime.p7s Type: application/pkcs7-signature Size: 2398 bytes Desc: not available Url : http://www.math.louisville.edu/pipermail/macgroup/attachments/20060113/9ac6166a/attachment.bin
