Using Duplicity and Amazon S3 – Notes and Examples

Up until now I’ve been doing my backups to Amazon S3 using my s3backup script. While it’s simple and does what I needed at the time, I’ve decided to cut some of the costs by switching to incremental backups.

I went on to define what I’m looking for, and after a short search I’ve came up with duplicity which support efficient incremental backups to Amazon S3 (among many other backends). While duplicity has an simple CLI interface, I did come across two pitfalls when using S3.

The first one is that one must export the AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY or else you get a error message from the underlying boto library:

  File "//usr/lib64/python2.5/site-packages/boto/", line 148, in __init__
    self.hmac =, digestmod=sha)
AttributeError: S3Connection instance has no attribute 'aws_secret_access_key'

The second thing to note is that is the way to specify buckets for duplicity. Instead of


which is used by s3cmd (which is a great tool), it asks to specify it using


Being aware of these points can save some time and frustration. In order to automate the backup process one can use cron. For example add the following to your crontab

0 1 * * 0  duplicity --no-encryption <folder-to-backup> s3+http://<bucket-name>/<prefix> &>> ~/backups.log

I unset the environment variables, so it won’t leak to other cron jobs unnecessarily.

2 thoughts on “Using Duplicity and Amazon S3 – Notes and Examples”

  1. Just a quick note… Duplicity now uses boto with regards to S3 commands. Therefore instead of setting the environment variables (AWS_…) one only needs to add a file in the user’s home directory called ‘.boto’ that contains the following:

    aws_access_key_id =
    aws_secret_access_key =

  2. Worth noting that if you have non-US buckets then you may need to add in:

    –s3-use-new-style –s3-european-buckets

    as cmdline params for duplicity

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