Today I’ve faced problem with syncing two github repositories. Yes, I know, I shouldn’t keep two, but sometimes it’s difficult to avoid. Anyway, the problem is super easy to solve. It’s enough to edit `.git/config` by adding new remote:

[remote "Origin"]
    url = git@github.com:user1/repo1.git
    url = git@github.com:user2/repo2.git

Of course, more than two repos can be added. Then, after next push all repositories will be synced.

git push Origin master

Everything up-to-date

Counting objects: 61, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (61/61), done.
Writing objects: 100% (61/61), 5.73 KiB | 0 bytes/s, done.
Total 61 (delta 41), reused 0 (delta 0)
To git@github.com:user2/repo2.git
   8b97528..8aed8c2  master -> master

Inspired by ruiabreu.