If you get the following error while syncing your seafile library with a server using a self signed certificate, you have to add the certficate to your certificate store.

Error:

urllib2.URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:581)>

Solution:

1. Retrieve the self-signed certificate (usually .pem or .crt)
2. Make sure you have ca-certificates installed

   apt-get install ca-certificates

3. Copy your certificate into the certificate folder

   cp cert.pem /usr/share/ca-certificates

4. Activate the certificate

   dpkg-reconfigure ca-certificates

For more information see: http://unix.stackexchange.com/a/90607