The underlying BSD subsystem of Mac OS X, Darwin, uses a unix-style permissions system to determine who can see, access, search and execute files, folders and devices.
Installer packages (.pkg and .mpgk) install software and puts files in various locations throughout your filesystem. The Installer also keeps receipts of these installations to facilitate keeping permissions up to date.
Many, many, many seeminlgy random problems in OS X can be caused by permissions problems; repairing permissions is usually the first step recommended in troubleshooting a problem in OS X.
Instead of waiting for a problem to crop up, why not set up your Mac to automatically repair permissions every night ? Here's how (you'll need administrator access) :
1. Open Terminal.app and type
sudo pico -w /etc/crontab and enter your password.
2. You should see a file that has contents similar to this:
Code:
# /etc/crontab
SHELL=/bin/sh
PATH=/etc:/bin:/sbin:/usr/bin:/usr/sbin
HOME=/var/log
#
#minute hour mday month wday who command
#
#*/5 * * * * root /usr/libexec/atrun
#
# Run daily/weekly/monthly jobs.
15 3 * * * root periodic daily
30 4 * * 6 root periodic weekly
30 5 1 * * root periodic monthly
10 * * * * root /sw/sbin/anacron -s
Go to the bottom of the file and add the following line (note: the spaces are tabs!)
Code:
# /etc/crontab
SHELL=/bin/sh
PATH=/etc:/bin:/sbin:/usr/bin:/usr/sbin
HOME=/var/log
#
#minute hour mday month wday who command
#
#*/5 * * * * root /usr/libexec/atrun
#
# Run daily/weekly/monthly jobs.
15 3 * * * root periodic daily
30 4 * * 6 root periodic weekly
30 5 1 * * root periodic monthly
10 * * * * root /sw/sbin/anacron -s
# Repair Permissions, added by me.
0 1 * * * root /usr/sbin/diskutil repairPermissions /
This will, every day at 01h00, repair permissions on the startup volume. Change the frequency to whatever you want, to a different time, once a week, whatever.
Alternatively you can use an application like
CronniX, instead of the Terminal, to add the line to the system crontab.