Heroku: Cannot run more than 1 Free size dynos

Had the exact same issue and came to this page. After reading realized what was going on but want to add following.

just run

heroku kill DYNO --app your_app_name

After this close all open consoles.

Then run db migrate command, it will work.

Most Efective

in console run:

heroku ps

the result is some like this:

run.4859 (Free): up 2016/01/12 21:28:41 (~ 7m ago): rails c

So the numbers 4859 represent the session that is open and needs to be closed. To fix the error you need to run(Obviusly, replace the number 4859 by the number obtained):

heroku ps:stop run.4859

It is a very simple solution.

In my case, I ran heroku ps:restart to restart all dynos and the heroku run * command worked again.

Examples

If you just have one Git remote for Heroku, use this:

heroku ps:restart && heroku run *

If you have multiple Git remotes for Heroku, use this:

heroku ps:restart --remote your-remote-name && heroku run * --remote your-remote-name

OR

heroku ps:restart --app your-heroku-app-name && heroku run * --app your-heroku-app-name

Replace * with your command e.g. console for Rails console.

---

What I meant by your-heroku-app-name here is the sub-domain for your Heroku app. For example, if your app URL is https://cute-cat.herokuapp.com, that means your-heroku-app-name is cute-cat.

If you are not sure/forgot what's your Git remote name for Heroku, git remote -v can help you with that.

Example:

$ git remote -v
this-is-the-remote-name      https://git.heroku.com/xxx.git (fetch)
this-is-the-remote-name      https://git.heroku.com/xxx.git (push)
this-is-another-remote-name  https://git.heroku.com/yyy.git (fetch)
this-is-another-remote-name  https://git.heroku.com/yyy.git (push)

The answer is to look for any open heroku sessions (you can use 'heroku ps' as john points out above), in my case I already had a started a heroku console session 30mins earlier and just forgot about it. So if you see the "Cannot run more than 1 Free size dynos" error just close any existing console or other heroku sessions you have open.

Hopefully this saves someone the ten minutes it took me to come to my senses.