Cannot add-apt-repository ppa:nemh/systemback on ubuntu 14.04

Добавьте PPA к источникам программного обеспечения:

sudo apt-add-repository ppa:nemh/systemback

... и Вы будете видеть что-то вроде этого:

 Simple system backup and restore application with extra features

Systemback makes it easy to create backups of the system and the users configuration files. In case of problems you can easily restore the previous state of the system. There are extra features like system copying, system installation and Live system creation.

This PPA contain the stable version of Systemback.

Currently supported Ubuntu releases:
- 14.04.X LTS
- 15.04
- 15.10
 More info: https://launchpad.net/~nemh/+archive/ubuntu/systemback
Press [ENTER] to continue or ctrl-c to cancel adding it

gpg: keyring `/tmp/tmpiv2ysmqh/secring.gpg' created
gpg: keyring `/tmp/tmpiv2ysmqh/pubring.gpg' created
gpg: requesting key 73C62A1B from hkp server keyserver.ubuntu.com
gpg: /tmp/tmpiv2ysmqh/trustdb.gpg: trustdb created
gpg: key 73C62A1B: public key "Launchpad PPA for Kendek" imported
gpg: Total number processed: 1
gpg:               imported: 1  (RSA: 1)
OK

Ответ @A.B должен хорошо работать, но в случае, если Вы все еще добираетесь, та же ошибка -

Откройте терминал и выполните:

sudo apt-get install --reinstall ca-certificates

и добавляют PPA...

sudo add-apt-repository ppa:nemh/systemback

_{ссылка здесь}