How do I attach an unnamed tmux session?

Question

tmux ls gives me the following result:

ubuntu@ip-10-x-y-z:~$ tmux ls
0: 1 windows (created Wed Aug 23 08:35:32 2017) [112x51]
1: 1 windows (created Wed Aug 23 09:06:27 2017) [112x51]

How do I attach the the first one in the list?

Answer 1

Your own answer is one way, with -t.

If you are already in one tmux session, you can PREFIX+s to let tmux show you a session list, thus, you can select the session you want to attach.

Or just tmux attach to attach the first session, then do the above step.

Answer 2

I have figured out the answer:

tmux attach -t 0

0 and 1 are the pid's of the sessions and they can be attached using those pid's after the attach command.