This essay by Alvin Boyd Kuhn explains it all, and it blew my mind. Good reading for an Easter weekend.

• Spiritual Symbolism of the Sun and Moon

Teresa and I use a single Dropbox account to share files between our computers. I also use the same account to store (and sync) plain-text notes on my iPad and iPhone (I use the apps PlainText and iA Writer). In case things go wrong with these apps, the syncing, or with Dropbox itself, I want to backup my Dropbox files and keep past snapshots of the backups so I can go back in time.

The Solution

rdiff-backup can do this. It is a command-line tool written in Python that:

…backs up one directory to another, possibly over a network. The target directory ends up a copy of the source directory, but extra reverse diffs are stored in a special subdirectory of that target directory, so you can still recover files lost some time ago. The idea is to combine the best features of a mirror and an incremental backup.

To make this all happen, I have Dropbox installed, signed-in, and running on my Linux desktop/server, which runs Ubuntu 11.04 Natty with Gnome 2.

Install rdiff-backup thusly:

    # aptitude install rdiff-backup

I use the directory /backup/ to hold all my backup targets, so I can run rdiff-backup like this:

    $ rdiff-backup  \
        --exclude $HOME/Dropbox/.dropbox \
        --exclude $HOME/Dropbox/.dropbox.cache \
        $HOME/Dropbox /backup/Dropbox

Every time I run rdiff-backup like this, it creates a new snapshot of my Dropbox files. Old snapshots are kept until I decide to purge them (if at all). To purge any snapshots older than two months, for example, I run this command:

    $ rdiff-backup --force --remove-older-than 2M /backup/Dropbox

I run the above two commands in an @hourly crontab script to keep this all happening automatically.

Browsing Past Snapshots

rdiff-backup has its own commands for digging into the files stored in the past snapshots, but it requires exactly knowing the filenames and backup times. Another tool, rdiff-backup-fs solves this problem by mounting the rdiff-backup backup directory as a FUSE filesystem, allowing me to grep and find my way through a directory tree of all snapshots.

After installing FUSE and rdiff-backup-fs, I mount my Dropbox snapshot tree with this command:

    $ rdiff-backup-fs ~/mnt /backup/Dropbox

Note that the order of the arguments for mounting source and target are backwards compared to the canonical mount command.

A long listing of my 10-oldest snapshots looks like this:

    $ ls -lF ~/mnt/ | head -10
    total 0
    dr-xr-xr-x 1 root root 4096 2013-03-10 13:52 2013-01-06T05:00:01/
    dr-xr-xr-x 1 root root 4096 2013-03-10 13:52 2013-01-06T06:00:01/
    dr-xr-xr-x 1 root root 4096 2013-03-10 13:52 2013-01-06T07:00:01/
    dr-xr-xr-x 1 root root 4096 2013-03-10 13:52 2013-01-06T08:00:01/
    dr-xr-xr-x 1 root root 4096 2013-03-10 13:52 2013-01-06T09:00:01/
    dr-xr-xr-x 1 root root 4096 2013-03-10 13:52 2013-01-06T10:00:01/
    dr-xr-xr-x 1 root root 4096 2013-03-10 13:52 2013-01-06T11:00:01/
    dr-xr-xr-x 1 root root 4096 2013-03-10 13:52 2013-01-06T12:00:01/
    dr-xr-xr-x 1 root root 4096 2013-03-10 13:52 2013-01-06T13:00:01/

I can then explore all my snapshots at once with any tools wish.

When done, I unmount the rdiff-backup-fs filesystem with:

    $ /bin/fusermount -u ~/mnt

I had two problems with this file: (1) Windows would not boot, so I couldn’t run the file using Windows. (2) The laptop had no floppy drive, so I couldn’t easily boot into DOS.

Now, one can solve this problem by booting from a FreeDOS LiveCD to run the file. But then you have to figure out how to get and run the MX51_A04.EXE file from within the FreeDOS environment. Various websites suggested methods using USB flash drives, but I couldn’t get this to work.

Instead, I was able to add the file to the LiveCD ISO image before I burnt the CD. Here’s how it worked:

1. Download the FreeDOS LiveCD called fdfullcd.iso (153MB).
2. Under Linux or Windows, install and run ISO Master.
3. Load the fdfullcd.iso in ISO Master and then add the MX51_A04.EXE file to it.
4. Save the modified ISO under a new name.
5. Burn the modified ISO to a CD and boot from that.
6. When you boot the laptop using this modified FreeDOS LiveCD, be sure to choose the LiveCD mode and not the install option.
7. Once you have a DOS prompt, the command X: will switch you to the X: drive, where you’ll find the contents of the CD and the BIOS update file.
8. Run it, cross your fingers, and reboot.

I like using the online dictionary at die.net because it’s fast and clean.

It’s easy to query, also. Just append your word to the end of the URL. For example:

• dictionary.die.net/spam

It describes itself as offering “free cross-referenced definitions, spelling correction, and word searches from WordNet, Webster’s, FOLDOC, and a variety of specialized sources.”

In the “spam” entry above, some of the sources include the Free On-Line Dictionary of Computing, the Virtual Entity of Relevant Acronyms, and the Jargon File.

This answer, which purposefully ignores the original poster’s restriction, says it best:

My take is still Emacs or vi. Even for a beginner.

Why?

Because time invested in learning an editor is productive only as long as you keep using that editor. All those less expressive options are poor choices for the long run, and will be abandoned eventually. At which point the time spent learning them is wasted, and the user still has to learn Emacs or vi.

In other words, the best (most expressive) tool for the job is one of Emacs or vi, and so you’ll eventually switch to one of them. It ultimately doesn’t matter which one you choose, but you would be smart to invest yourself into learning one of them.

For the record, I’m a vim user, and I love using it.

I just learned tonight that Wil Wheaton has a new podcast out, called Memories of the Futurecast.

The podcast is a promotion of his latest book, Memories of the Future, Volume One, which is Wil’s going-down-memory-lane review of the first 13 episodes of Star Trek: The Next Generation.

I listened to the first episode of the podcast already, and I’m looking forward to hearing the rest (12 of 13 have been published so far, as I write this). I enjoy everything Wil Wheaton does.

Check it out.