Creating Encrypted FTP Backups With duplicity And duply On Debian Squeeze

Version 1.0
Author: Falko Timme
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When you rent a dedicated server nowadays, almost all providers give you FTP backup space for your server on one of the provider's backup systems. This tutorial shows how you can use duplicity and duply to create encrypted (so that nobody with access to the backup server can read sensitive data in your backups) backups on the provider's remote backup server over FTP. duply is a duplicity wrapper script that allows us to use duplicity without interaction (i.e., you do not have to type in any passwords).

I do not issue any guarantee that this will work for you!


1 Preliminary Note

In this tutorial I call the backup server where I have an FTP account with the username backupuser and the password secret. On my own server, I want to backup the directory /home/exampleuser.


2 Installing duplicity

First we make sure our system is up-to-date:

apt-get update
 apt-get upgrade 

Then we install duplicity as follows:

apt-get install duplicity ncftp 


3 Our First Backup

Now let's do our first backup:

FTP_PASSWORD=secret duplicity /home/exampleuser ftp://[email protected]/

[email protected]:/home/exampleuser# FTP_PASSWORD=secret duplicity /home/exampleuser ftp://[email protected]/
NcFTP version is 3.2.4
GnuPG passphrase:
Local and Remote metadata are synchronized, no sync needed.
Last full backup date: none
No signatures found, switching to full backup.
Retype passphrase to confirm:
--------------[ Backup Statistics ]--------------
StartTime 1341339005.14 (Tue Jul 3 20:10:05 2012)
EndTime 1341339006.46 (Tue Jul 3 20:10:06 2012)
ElapsedTime 1.32 (1.32 seconds)
SourceFiles 53
SourceFileSize 13494139 (12.9 MB)
NewFiles 53
NewFileSize 13494139 (12.9 MB)
DeletedFiles 0
ChangedFiles 0
ChangedFileSize 0 (0 bytes)
ChangedDeltaSize 0 (0 bytes)
DeltaEntries 53
RawDeltaSize 13461371 (12.8 MB)
TotalDestinationSizeChange 4687992 (4.47 MB)
Errors 0

[email protected]:/home/exampleuser#

As you see you will be asked for a GnuPG passphrase. You can type in any password you like; this has to be done everytime you run duplicity. The backup will be encrypted with the help of GnuPG. Permissions and ownerships will be preserved in the backup.

To create the backup in a subdirectory on the backup server, you'd modify the command as follows:

FTP_PASSWORD=secret duplicity /home/exampleuser ftp://[email protected]/subdirectory

When you run duplicity for the first time, it will create a full backup; afterwards, it creates incremental backups. To force the creation of a full backup again, you can use the full switch:

FTP_PASSWORD=secret duplicity full /home/exampleuser ftp://[email protected]/

To exclude a directory from the backup, e.g. /home/exampleuser/tmp, you can use the --exclude switch:

FTP_PASSWORD=secret duplicity --exclude /home/exampleuser/tmp /home/exampleuser ftp://[email protected]/

If you are backing up the root directory /, remember to --exclude /proc, or else duplicity will probably crash.

To learn more about the available duplicity options, take a look at

man duplicity


4 Restore A Backup

Now let's assume we have deleted everything in /home/exampleuser and want to restore it from our FTP backup. This is how it's done:

FTP_PASSWORD=secret duplicity ftp://[email protected]/ /home/exampleuser

Please note that in this case the remote location comes before to local folder!


5 Automatic Backups With duply

Because duplicity asks for a GnuPG password everytime we use it, it's hard to use it for automatic backups (e.g. via cron). Fortunately there's duply, a duplicity wrapper script, which allows us to call duplicity without being asked for a password.

First we generate a GnuPG key that duply will use (so that we don't have to type in a password anymore):

gpg --gen-key

server1:/home/exampleuser# gpg --gen-key
gpg (GnuPG) 1.4.10; Copyright (C) 2006 Free Software Foundation, Inc.
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions. See the file COPYING for details.

Please select what kind of key you want:
   (1) DSA and Elgamal (default)
   (2) DSA (sign only)
   (5) RSA (sign only)
Your selection? <-- ENTER
DSA keypair will have 1024 bits.
ELG-E keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048)
 <-- ENTER
Requested keysize is 2048 bits
Please specify how long the key should be valid.
         0 = key does not expire
      <n>  = key expires in n days
      <n>w = key expires in n weeks
      <n>m = key expires in n months
      <n>y = key expires in n years
Key is valid for? (0)
 <-- ENTER
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) <[email protected]>"

Real name:
 <-- your name, e.g. Falko Timme
Email address: <-- your email address, e.g. [email protected]
You selected this USER-ID:
    "Falko Timme <[email protected]>"

Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit?
 <-- O
You need a Passphrase to protect your secret key. <-- Type in your desired password (twice to confirm it)

Now the key will be generated. It's a good idea to open a second console and type some letters so that the random number generator can 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.
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: /root/.gnupg/trustdb.gpg: trustdb created
gpg: key 
7C6E958B marked as ultimately trusted
public and secret key created and signed.

gpg: checking the trustdb
gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
gpg: depth: 0  valid:   1  signed:   0  trust: 0-, 0q, 0n, 0m, 0f, 1u
pub   1024D/7C6E958B 2007-12-10
      Key fingerprint = 1FDC 60FB 8A27 90D8 553C  3C3E 8E1F 66F7 7C6E 958B
uid                  Falko Timme <[email protected]>
sub   2048g/F1BB98F4 2007-12-10


I've highlighted the key ID (7C6e958B) because we'll need it in a moment.

Next we download duply:

cd /tmp
tar xvfz duply_1.5.7.tgz
cp duply_1.5.7/duply /usr/local/bin

To use duply, we need to create at least one profile. Since I back up /home/exampleuser in this tutorial, I call the profile exampleuser. We can create the profile as follows:

duply exampleuser create

This creates the directory /root/.duply/exampleuser with the duply configuration file conf in it. Open the file:

vi /root/.duply/exampleuser/conf 

The most important settings in this file are:

  • GPG_KEY: the ID of our GnuPG key;
  • GPG_PW: the password we typed in when we created the GnuPG key;
  • TARGET: the backup server (incl. the FTP username);
  • TARGET_PASS: the FTP password in the backup server;
  • SOURCE: the source directory (i.e., the directory to be backed up);
  • MAX_AGE: the age of the oldest backup; older backups will be deleted;
  • VERBOSITY: amount of information displayed on the screen by duply;
  • TEMP_DIR: a directory for temporary files; when you restore a backup, this directory must at least have enough space for the biggest file in the backup.

My file looks as follows

# gpg encryption settings, simple settings:
#  GPG_KEY='disabled' - disables encryption alltogether
#  GPG_KEY='<key1>[,<key2>]'; GPG_PW='pass' - encrypt with keys, sign
#    with key1 if secret key available and use GPG_PW for sign & decrypt
#  GPG_PW='passphrase' - symmetric encryption using passphrase only
# gpg encryption settings in detail (extended settings)
#  the above settings translate to the following more specific settings
#  GPG_KEYS_ENC='<keyid1>,[<keyid2>,...]' - list of pubkeys to encrypt to
#  GPG_KEY_SIGN='<keyid1>|disabled' - a secret key for signing
#  GPG_PW='<passphrase>' - needed for signing, decryption and symmetric
#   encryption. If you want to deliver different passphrases for e.g.
#   several keys or symmetric encryption plus key signing you can use
#   gpg-agent. Add '--use-agent' to the duplicity parameters below.
#   also see "A NOTE ON SYMMETRIC ENCRYPTION AND SIGNING" in duplicity manpage
# notes on en/decryption
#  private key and passphrase will only be needed for decryption or signing.
#  decryption happens on restore and incrementals (compare archdir contents).
#  for security reasons it makes sense to separate the signing key from the
#  encryption keys.
# set if signing key passphrase differs from encryption (key) passphrase
# NOTE: available since duplicity 0.6.14, translates to SIGN_PASSPHRASE

# gpg options passed from duplicity to gpg process (default='')
# e.g. "--trust-model pgp|classic|direct|always"
#   or "--compress-algo=bzip2 --bzip2-compress-level=9"
#   or "--personal-cipher-preferences AES256,AES192,AES..."

# disable preliminary tests with the following setting

# credentials & server address of the backup target (URL-Format)
# syntax is
#   scheme://[user:[email protected]]host[:port]/[/]path
# probably one out of
#   file://[/absolute_]path
#   ftp[s]://user[:password][:port]/some_dir
#   hsi://user[:password]
#   cf+http://container_name
#   imap[s]://user[:password][/from_address_prefix]
#   rsync://user[:password][:port]::/module/some_dir
#   # rsync over ssh (only keyauth)
#   rsync://[email protected][:port]/relative_path
#   rsync://[email protected][:port]//absolute_path
#   # for the s3 user/password are AWS_ACCESS_KEY_ID/AWS_SECRET_ACCESS_KEY
#   s3://[user:password]@host/bucket_name[/prefix]
#   s3+http://[user:password]@bucket_name[/prefix]
#   # scp and sftp are aliases for the ssh backend
#   ssh://user[:password][:port]/some_dir
#   tahoe://alias/directory
#   webdav[s]://user[:password]
# ATTENTION: characters other than A-Za-z0-9.-_.~ in user,password,path have
#            to be replaced by their url encoded pendants, see
#            if you define the credentials as TARGET_USER, TARGET_PASS below
#            duply will url_encode them for you
TARGET='ftp://[email protected]/'
# optionally the username/password can be defined as extra variables
# setting them here _and_ in TARGET results in an error

# base directory to backup

# exclude folders containing exclusion file (since duplicity 0.5.14)
# Uncomment the following two lines to enable this setting.
#DUPL_PARAMS="$DUPL_PARAMS --exclude-if-present '$FILENAME'"

# Time frame for old backups to keep, Used for the "purge" command.
# see duplicity man page, chapter TIME_FORMATS)

# Number of full backups to keep. Used for the "purge-full" command.
# See duplicity man page, action "remove-all-but-n-full".

# activates duplicity --full-if-older-than option (since duplicity v0.4.4.RC3)
# forces a full backup if last full backup reaches a specified age, for the
# format of MAX_FULLBKP_AGE see duplicity man page, chapter TIME_FORMATS
# Uncomment the following two lines to enable this setting.
#DUPL_PARAMS="$DUPL_PARAMS --full-if-older-than $MAX_FULLBKP_AGE "

# sets duplicity --volsize option (available since v0.4.3.RC7)
# set the size of backup chunks to VOLSIZE MB instead of the default 25MB.
# VOLSIZE must be number of MB's to set the volume size to.
# Uncomment the following two lines to enable this setting.

# verbosity of output (error 0, warning 1-2, notice 3-4, info 5-8, debug 9)
# default is 4, if not set

# temporary file space. at least the size of the biggest file in backup
# for a successful restoration process. (default is '/tmp', if not set)

# Modifies archive-dir option (since 0.6.0) Defines a folder that holds
# unencrypted meta data of the backup, enabling new incrementals without the
# need to decrypt backend metadata first. If empty or deleted somehow, the
# private key and it's password are needed.
# NOTE: This is confidential data. Put it somewhere safe. It can grow quite
#       big over time so you might want to put it not in the home dir.
# default '~/.cache/duplicity/duply_<profile>/'
# if set  '${ARCH_DIR}/<profile>'

# DEPRECATED setting
# sets duplicity --time-separator option (since v0.4.4.RC2) to allow users
# to change the time separator from ':' to another character that will work
# on their system.  HINT: For Windows SMB shares, use --time-separator='_'.
# NOTE: '-' is not valid as it conflicts with date separator.
# ATTENTION: only use this with duplicity < 0.5.10, since then default file
#            naming is compatible and this option is pending depreciation
#DUPL_PARAMS="$DUPL_PARAMS --time-separator _ "

# DEPRECATED setting
# activates duplicity --short-filenames option, when uploading to a file
# system that can't have filenames longer than 30 characters (e.g. Mac OS 8)
# or have problems with ':' as part of the filename (e.g. Microsoft Windows)
# ATTENTION: only use this with duplicity < 0.5.10, later versions default file
#            naming is compatible and this option is pending depreciation
#DUPL_PARAMS="$DUPL_PARAMS --short-filenames "

# more duplicity command line options can be added in the following way
# don't forget to leave a separating space char at the end
#DUPL_PARAMS="$DUPL_PARAMS --put_your_options_here "
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2 Comment(s)

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By: linux guy

This is what i am looking for. Its a good article on using ftp command for taking backups.

By: Tom

It's important to mention to keep your GnuPG keys somewhere safe off the Server you are backing up. You can just copy the directory /root/.gnupg/ and all contents to a safe place.

If you lose your gpg keys in case of hardware failure, or forget your passphrase, your backup is useless.

 True story :(