Copy with ssh-copy-id

If you have ssh access to the machine with a password, you can use ssh-copy-id.

$ ssh-copy-id user@host
# or to specify the key
$ ssh-copy-id -i ~/.ssh/mykey user@host

Using Git Platforms

Both GitHub and GitLab allow you to grab a users public SSH keys.

You can grab them like so:

$ curl https://github.com/<username>.keys
$ curl https://gitlab.com/<username>.keys

# And I would:
$ curl https://github.com/tryton-vanmeer.keys
$ curl https://gitlab.com/tryton-vanmeer.keys

And to add the keys to a machine you have access to:

curl https://github.com/tryton-vanmeer.keys | tee -a ~/.ssh/authorized_keys

You would now be able to SSH into that machine using any machine that has SSH access to your Git platforms.

Permissions

If the SSH folder had to be created for a user, make sure the permissions are correctly set for the folder itself, and the authorized_keys file.

$ chmod 700 ~/.ssh
$ chmod 600 ~/.ssh/authorized_keys