Ubuntu – Limit the size of a directory by deleting old files

find -L files -type f -newerct '-7 days' -exec ln -s -t recent-files {} +

(Of course, change "files" and "recent-files" as appropriate.)

The 'c' used in -newer isn't creation time, it's the "change" field as shown by stat (the command, e.g. man 1 stat). It's currently uncommon for *nix filesystems to store creation time, but change ('c'), modification ('m'), and access ('a') time is available. If your filesystem does store creation time, you can use 'B' ("birth time") — you'll get an immediate error message if it's unsupported.

You can see the exact cutoff with date:

$ date -d '-7 days'
Sat Oct 16 02:46:27 UTC 2010
$ date  # this was executed one second later
Sat Oct 23 02:46:28 UTC 2010

Instead of changing how the directory works, you could have a little clean-up script. It's easier to implement and probably less dangerous in the long run.

The following will delete anything over 7 days old in your ~/Download/ directory:

find ~/Download/ -mtime +7 -delete

You might want to test that by just removing the -delete segment and checking the files it returns. But once you're happy with it, you can schedule it to run once a day by running crontab -e and adding this on a new line:

@daily find ~/Download/ -mtime +7 -delete

ControlX then Y to save and exit and you're done.