How to fix "unmet dependencies" error with apt

Question

I entered the following command on ubuntu 14.04

sudo apt-get install python3.6-dev libmysqlclient-dev

It gives the following error

The following packages have unmet dependencies:

 libmysqlclient-dev : Depends: libmysqlclient18 (= 5.5.59-0ubuntu0.14.04.1) but 10.2.13+maria~trusty is to be installed
W: Duplicate sources.list entry https://repo.skype.com/deb/ stable/main amd64 Packages (/var/lib/apt/lists/repo.skype.com_deb_dists_stable_main_binary-amd64_Packages)
W: You may want to run apt-get update to correct these problems
E: Unable to correct problems, you have held broken packages.

Answer 1

You have MariaDB installed instead of MySQL, and are trying to install MySQL's version of the development package. That results in a dependency conflict. The equivalent MariaDB package is named slightly differently: it's libmariadb-dev.

libmariadb-dev also has a Provides: libmysqlclient-dev in its package metadata, so it will satisfy any dependencies for libmysqlclient-dev.

So try:

sudo apt-get install python3.6-dev libmariadb-dev

---

To clear the warning about the Skype repository, check your /etc/apt/sources.list file and all files in the /etc/apt/sources.list.d/ directory, and ensure that the Skype repository is mentioned only once.

The newer Skype packages will drop a repository configuration file into /etc/apt/sources.list.d/ directory, while older ones didn't so you've probably added the Skype repository manually. Now you can remove your manual addition.