次のコマンドを実行します（好ましくは別名それを作る）：
$ tmux new-session -A -s [session-name]
旗の意味：
-s refers to session name.
-A In case session-name exists, command will act like attach-session instead of new-session.
公式ドキュメントのmanページを参照してください。
$ man tmux
new-session [-AdDEP] [-c start-directory] [-F format] [-n window-name] [-s session-name] [-t
target-session] [-x width] [-y height] [shell-command]
(alias: new)
Create a new session with name session-name.
The new session is attached to the current terminal unless -d is given. window-name and
shell-command are the name of and shell command to execute in the initial window. If -d
is used, -x and -y specify the size of the initial window (80 by 24 if not given).
If run from a terminal, any termios(4) special characters are saved and used for new win‐
dows in the new session.
The -A flag makes new-session behave like attach-session if session-name already exists;
in this case, -D behaves like -d to attach-session.
If -t is given, the new session is grouped with target-session. This means they share
the same set of windows - all windows from target-session are linked to the new session,
any new windows are linked to both sessions and any windows closed removed from both ses‐
sions. The current and previous window and any session options remain independent and
either session may be killed without affecting the other. -n and shell-command are
invalid if -t is used.
The -P option prints information about the new session after it has been created. By
default, it uses the format ‘#{session_name}:’ but a different format may be specified
with -F.
If -E is used, the update-environment option will not be applied.