fix_gids.sh

# The OSX Mavericks upgrade installer can totally corrupt group ownership of
# files in user home directories. Typically, it looks like the Mavericks installer
# simply sets (most? all?) of the files to the same gid as your uid, which may be nonsense.
# Specifically, most single-user OS X installs have uid=501 for the default user,
# so gid is typically 501 too.

# Step 0: make sure your user is still part of its group:
dseditgroup -o edit -t user -a <your_user_name> <your_user_name>

# (The second occurence of <your_user_name> is actually the group name)

# Step 1: fix permissions
# run from root of your home directory
find . -gid 501 -exec chgrp <your_user_name> "{}" \;

# ... and now wait a while.