I'm writing a shell script that creates / attaches or switches to a given session, depending on whether one is inside tmux and the session exists.

I've got everything working great except for the case requiring the creation of a new tmux session from within a tmux session.

When my script executes tmux new-session -s name, I get the following output:

sessions should be nested with care, unset $TMUX to force

I don't actually want to nest sessions, my goal is to create another separate session and switch to it from within a tmux session.

Is this possible?

6 Answers

The quickest way (assuming you use ctrl-b as your command prefix) is:

ctrl-b :new 

To create a new session, then

ctrl-b s 

to interactively select and attach to the session.

How to create the script

This script will check if a session exists. If session does not exist create new session and attach to it. If session does exist nothing happens and we attach to that session. Feel free to replace `~/development' with project name.

$ touch ~/development && chmod +x ~/development

# ~/development tmux has-session -t development if [ $? != 0 ] then tmux new-session -s development fi tmux attach -t development 

New session from terminal

Let's create two detached sessions, list them, attach to one and then from within tmux cycle through sessions.

tmux new -s name -d works from inside tmux because we're creating a new detached session. Otherwise you'll get a nesting error.

$ tmux new -s development -d $ tmux new -s foo -d $ tmux ls > development: 1 windows (created Wed Jan 13 11:31:38 2016) [204x54] > foo: 1 windows (created Wed Jan 13 11:31:38 2016) [204x54] $ tmux attach -t $ tmux ls > development: 1 windows (created Wed Jan 13 11:31:38 2016) [204x54] (attached) > foo: 1 windows (created Wed Jan 13 11:31:38 2016) [204x54] 

New session from within tmux

We are now inside or better known as attached to our target session. If we try to create a new session while attached it will result in a nesting error.

$ tmux new -s bar > sessions should be nested with care, unset $TMUX to force 

To solve this we create a new detached session. e.g.,

$ tmux new -s bar -d $ tmux ls > development: 1 windows (created Wed Jan 13 11:31:38 2016) [204x54] (attached) > foo: 1 windows (created Wed Jan 13 11:31:38 2016) [204x54] > bar: 1 windows (created Wed Jan 13 17:19:35 2016) [204x54] 

Cycle (switch) Sessions

• Prefix ( previous session
• Prefix ) next session

note: Prefix is Ctrl-bby default. You can bind Prefix to Ctrl-a and in Mac OSX you can change Caps Lock to ctrl system preferences > keyboard > modifier keys

Attach to a session using command mode while inside tmux

Trying to attach to a session without detaching will result in an error.

$ tmux attach -t development > sessions should be nested with care, unset $TMUX to force 

Instead use command mode Prefix : then type attach -t session_name and hit enter.

Using this works for me:

TMUX= tmux new-session -d -s name tmux switch-client -t name 

The TMUX= on the first line is required so tmux doesn't throw a sessions should be nested with care, unset $TMUX to force message.

All the commands you can launch within your terminal, like tmux new -s sessionName can be launched from within tmux by pressing the trigger key (eg: ctrl-b) then : then the command without the starting tmux part.

As a result, ctrl-b : followed by new -s sessionName will do exactly what you want and give a name to your session. It also switches automatically to the new session.

You can try unset TMUX first, this works for me.

at user2354696's advice I use following key bindings to create a new session or "clone" an existing session

 bind-key N run-shell 'TMUX= tmux new-session -d \; switch-client -n' bind-key C run-shell 'TMUX= tmux new-session -t $(tmux display-message -p #S) -s $(tmux display-message -p #S-clone) -d \; switch-client -n \; display-message "session #S cloned"'