Dropbox

Please note that TCM in no way recommends Dropbox. This page exists merely for the amusement of current addicts. It follows the old Cambridge convention of using the string "spqr1" where your user-name is required.

The free, commercial, Dropbox computer synchronisation software makes the usual tedious assumptions about home directories being large, and not shared between multiple computers. However, a little skill soon enables it to work reasonably in TCM.

The TCM-provided version of dropbox makes the directory synchronised as /scratch/spqr1/Dropbox, and places its configuration files in /scratch/spqr1/.dropbox. Thus each PC on which you run Dropbox has a different configuration directory, and a different directory to synchronise.

The following commands are provided:
dropbox or dropbox start starts the dropbox Daemon
dropbox stop stops the Dropbox daemon
dropbox sync runs the daemon for as long as is necessary to synchronise
dropbox status is equivalent to dropbox.py status
dropbox.py is the standard python script provided with Dropbox.

If Dropbox can connect to an X server, it will exit when that connection is broken (e.g. you log out). If not (e.g. sshing without X forwarding), the TCM scripts above will ensure that the Dropbox daemon gets killed after 12 hours.

Warnings

Whilst Dropbox is quite good at taking care of data, it should be treated gently. Things which are not trivially mapped to equivalents in UNIX, MacOS, Windows, Android, etc., tend to go a little wrong. In particular, Dropbox is liable to change permissions (so take care if you don't like your files to be world readable, and don't be too surprised if they end up world writable). It also behaves poorly with links (hard or soft), or with files whose names are identical save for changes in case.

The first time you run Dropbox in TCM, you may need to choose "Open my Dropbox Folder" to get it to complete the installation process.

Other Notes

Files in Dropbox are presumably well backed up, both by Dropbox, and by being distributed across multiple locations. Backing them up again by placing them in one's home directory, rather than /scratch, seems pointless. Anyway, Dropbox works badly with NFS directories, as its use of the select system call to detect changes does not work as it expects.

In its default configuration, before TCM modifications, it places its configuration files in one's home directory, including a note to say if it is running. Start it on pc52, and it is happy. Start it again on pc51, and it seems happy - it appears to believe that the previous instance of itself has died. Stop it on either, and although the other instance will continue running, attempts to stop that final instance will now fail, as its configuration says that the last thing to happen was its successful exit. So you end up with a daemon that you cannot easily stop.

There are many, many sensible ways of copying data between /scratch disks in TCM, and Dropbox is not one as it will copy the data via a remote server. Use rcp, scp, ssh+tar, rsync, ... The following four examples all work fine for copying the given directory and all its subdirectories. None needs a password between TCM machines.

pc0:/scratch/spqr1$ rcp -r i2c pc52:/scratch/spqr1/
pc0:/scratch/spqr1$ scp -r i2c pc52:/scratch/spqr1/
pc0:/scratch/spqr1$ tar -cf - i2c | ssh pc52 tar -C /scratch/spqr1 -xf -
pc0:/scratch/spqr1$ rsync -a i2c pc52:/scratch/spqr1/

Dropbox and Privacy

Dropbox moves data you give it outside of the EEA. It is possible that its current privacy policy is suitable for personal data (though my personal judgement would be that it is not). However, the policy currently (Nov 2013) also states "if we are involved in a merger, acquisition, or sale [...] we will notify you (for example, via email and/or a prominent notice on our website) of any change in control or use of your Personal Information or Files, or if either become subject to a different Privacy Policy." That seems to say that subject to placing a prominent notice on its website to say that selling your files to any bidders is its new intention, Dropbox, after a takeover, may do so. Unless you can guarantee to monitor its website (and many people use Dropbox without ever seeing a need to touch its website), that is clearly incompatible with anything remotely like personal or confidential data storage.

A Talk on Dropbox

These slides show why you do not wish to mix Dropbox and symlinks, amongst other things.