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I keep confidential data (docs, spreadsheets, images, etc) on USB sticks or discs. I plug/insert them to access the data when I need, and put them back in a drawer when I'm done.

  1. Does Ubuntu store this data (in cache, or somewhere else)

If yes...

  1. Where?
  2. For how long?
  3. How to delete this from Ubuntu?
  4. How to stop Ubuntu storing this data in the first place?

p.s.: I'm already aware of the cache directory to store image thumbnails, but I'm asking now in terms of the entire file being stored. Thanks.

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Does Ubuntu store this data (in cache, or somewhere else)

No.

Besides what is in memory because of usage on that system (and not synched data) there are no other locations where this is stored. And the "in memory" is lost when saved to disk or when rebooted. Basically this is active when you have software open with one of your files.

Come to think of it: there is 1 thing you need to keep an eye on: "activity journal". It is zeitgeist component that keeps an eye on files openened to help you find your files better.

There are also some other things to consider that leave traces of files:

  • gedit has a setting to save a backup (same filename ending in ~). Other software you use can have similar settings.
  • online storage can pick up your file if you store it on a system where that specific directory is linked to online storage. Technically someone could set a system up such that USB sticks are synched on connection.
  • data may also end up in the swap file. After the program is closed, the space that the data takes up in the swap file may be reused, but the contents won't be actively overwritten.
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    Technically, your sensitive data may also end up in the swap file. After the program is closed, the space that the data takes up in the swap file may be reused, but the contents won't be actively overwritten. – Jos Jul 18 '14 at 8:49
  • @jos indeed :) added and +1'd you – Rinzwind Jul 18 '14 at 8:52
  • Thanks you both. Can you please explain "the contents won't be actively overwritten" more? – Rodrigo Jul 19 '14 at 8:57
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    @Rodrigo your swap stays on your machine and does not get overwritten unless overwritten by something new. So if your files are put into swap (for speeding up processes) it will remain there and could be recreated. – Rinzwind Jul 19 '14 at 10:46
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Aside from the Zeitgeist logs Rinzwind mentioned you also have to worry about two files:

1.) recently-used.xbel. This is GNOME's old logging system. The file should be located somewhere around ~/.local/share

2.) Thumbnails. Ubuntu stores thumbnails of images and other formats by default. These thumbs are located at ~/.local/share/thumbnails or ~/.thumbnails on older releases

Of course there's also a lot of apps that have their own logs and histories (e.g. VLC, etc.).

In the end you have to realize that if you handle sensitive data on a machine you better make sure that the machine itself is also secure.

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