Monday, March 28, 2016

Backups with Duplicity and Dropbox

Dropbox is a very popular service for file storage, the way the service works will synchronize by default
all your files across your devices. This is important to know since you will be backing up data into
Dropbox and you don't want to download the backups on every device you have connected.

What we want to do is to backup files, encrypt them and send them to Dropbox.
All this is achieved with Duplicity.

This is the setup

  • Linux OS, any distro will work I guess but I tried on Ubuntu 14.04 LTS
  • Dropbox account (going pro or business is recommended since backups will typical grow over 2GB basic account)

To encrypt files you will need GPG, in case you don't have a key on your system
we need to do a bit of work, if you do have a gpg key you can skip the next section.

GPG Setup

In this section will create GPG public key/private keys that will be used to encrypt the data you backup to Dropbox.

# install
$ sudo apt-get install gnupg
# check if you have any keys
$ gpg --list-keys
# if this is empty than you need to create a set of keys
# follow the wizard to create keys
$ gpg --gen-key
gpg (GnuPG) 1.4.16; Copyright (C) 2013 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

gpg: keyring `/home/yourname/.gnupg/secring.gpg' created
Please select what kind of key you want:
   (1) RSA and RSA (default)
   (2) DSA and Elgamal
   (3) DSA (sign only)
   (4) RSA (sign only)
Your selection? 1
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048) 
Requested keysize is 2048 bits
Please specify how long the key should be valid.
         0 = key does not expire
        = key expires in n days
      w = key expires in n weeks
      m = key expires in n months
      y = key expires in n years
Key is valid for? (0) 
Key does not expire at all
Is this correct? (y/N) y

You need a user ID to identify your key; the software constructs the user ID
from the Real Name, Comment and Email Address in this form:
    "Heinrich Heine (Der Dichter) "

Real name: Your Name
Email address:
You selected this USER-ID:
    "Your Name "

Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? O
You need a Passphrase to protect your secret key.

We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.

We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.

gpg: checking the trustdb

# At this point the keys are created and saved into your keyring
# list keys
$ gpg --list-keys
pub   2048R/999B4B79 2016-03-26
            ^^^^^^^^ /used by duplicity
uid                  Your Name 
sub   2048R/99917D12 2016-03-26 

# Note 999B4B79 which is your keyid

Duplicity install

$ sudo apt-get install duplicity

After installation if you are on Ubuntu 14.04 LTS you will need to apply this patch
to /usr/lib/python2.7/dist-packages/duplicity/backends/
If you don't know how to apply the patch is simpler to open the file at line 75 and write the following

 72 def command(login_required=True):
 73     """a decorator for handling authentication and exceptions"""
 74     def decorate(f):
 75         def wrapper(self, *args):
 76             from dropbox import rest  ## line to add
 77             if login_required and not self.sess.is_linked():
 78               log.FatalError("dpbx Cannot login: check your credentials",log.ErrorCode.dpbx_nologin)

Dropbox and duplicity setup

You need to have an account first. Open your browser and login.

Backups with duplicity and dropbox

Since this is the first time you run it need to make a authorization token, this is done as follow

$ duplicity --encrypt-key 999B4B79 full SOURCE dpbx:///
Please authorize in the browser. After you're done, press enter.

Now into your browser authorize the application. This will create an access token into dropbox.
You can see the apps you have going to Security
Should see under Apps linked backend for duplicity
In case you need to know what token is in use you can see it onto you system ~/.dropbox.token_store.txt

Local and Remote metadata are synchronized, no sync needed.
Last full backup date: none
GnuPG passphrase: 
Retype passphrase to confirm: 
--------------[ Backup Statistics ]--------------
StartTime 1459031263.59 (Sat Mar 26 18:27:43 2016)
EndTime 1459031263.73 (Sat Mar 26 18:27:43 2016)
ElapsedTime 0.14 (0.14 seconds)
SourceFiles 2
SourceFileSize 1732720 (1.65 MB)
NewFiles 2
NewFileSize 1732720 (1.65 MB)
DeletedFiles 0
ChangedFiles 0
ChangedFileSize 0 (0 bytes)
ChangedDeltaSize 0 (0 bytes)
DeltaEntries 2
RawDeltaSize 1728624 (1.65 MB)
TotalDestinationSizeChange 388658 (380 KB)
Errors 0


When the first full backup finished you can start making incremental backups, list the backups etc.
# list the backup files
duplicity --encrypt-key 999B4B79 list-current-files dpbx:///

## Make an incremental backup

duplicity --encrypt-key 999B4B79 incr SOURCE dpbx:///

duplicity --encrypt-key 999B4B79 list-current-files dpbx:///


During a backup if you see something like

Attempt 1 failed. NameError: global name 'rest' is not defined
Attempt 2 failed. NameError: global name 'rest' is not defined

See the note about Ubuntu 14.04 because you need to patch the file


If you use multiple computers and don't want to download from dropbox all
the backups you need to enable selective sync and exclude the Apps/duplicity
folder from Dropbox.
I haven't used duplicity for long time and heard some mix opinions, some say is excellent and some
say has some design flows (didn't checked) where your full backup will be taken after a while even if
you just do incremental. Remains to be seen.
I guess if this doesn't work well I would look into Borg Backup which seems to be the best these days since
has dedup built in and many other features. One thing that doesn't though is many backends as duplicity which
can use pretty much all cloud storage solutions around :).