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I am trying to create an automated clean shutdown of my opensimulator servers.
On each server, I have several Tmux sessions. Inside each session, there are several windows. In the following example, there are only two sessions to keep things simple.
sara#opensim:~$ tmux ls
Robust: 5 windows (created Tue May 12 22:08:28 2020)
Simulators01: 6 windows (created Tue May 12 23:30:38 2020)
sara#opensim:~$
In the full version, there will be 10+ Simulator sessions.
What I want to do is use a shell script to select a specific session. Every session will have a closedown shell script which looks similar to this:
#!/usr/bin/env bash
SESSION="InstancesTesting"
echo "checking for session - $SESSION"
SESSIONEXISTS=$(tmux list-sessions | grep $SESSION)
if [ "$SESSIONEXISTS" != "" ]
then
echo "session found"
tmux attach-session -d -t $SESSION
tmux select-window -t '0821'
tmux send-keys -t '0821' 'quit' C-m
tmux select-window -t '0900'
tmux send-keys -t '0900' 'quit' C-m
tmux select-window -t '0901'
tmux send-keys -t '0901' 'quit' C-m
tmux select-window -t '0910'
tmux send-keys -t '0910' 'quit' C-m
tmux select-window -t '0911'
tmux send-keys -t '0911' 'quit' C-m
tmux select-window -t '0920'
tmux send-keys -t '0920' 'quit' C-m
echo "finished shut down call for $SESSION"
else
echo "session not found skipping"
fi
The problem line is
tmux attach-session -d -t $SESSION
When it is run from a shell script, everything after that stops until the session is detached. However, without attaching the session only the windows of the last attached session can be accessed.
I can't simply kill the session at the end of the quit commands because the simular running inside each window can take up to 10 mins to shut down. Neither do I want to wait 10 mins between starting each shutdown. I want to set them all going then wait for the processes to close before doing a reboot.
What I need is to either:
1. Attach a session and allow the script to keep running without pressing ctrl+b D to detach.
or
2. Change the session which is being accessed without actually attaching it like the above example.
I have also tried
tmux switch-client SessionName
tmux switch-client -t SessionName
tmux switch-client -n
All of these return the same result
no current client
I have also tried
tmux send-keys -t 'WindowName' 'tmux choose-session' C-m
tmux send-keys -t 'WindowName' '0' C-m
Unfortunately, this option also states there is no client.
I am sure this must be possible, I am going round in circles, please help
There is no concept of a "selected session", clients have an attached session but outside tmux when you don't specify a session the choice of which to use is made separately each time. See here: https://github.com/tmux/tmux/wiki/Advanced-Use#the-default-target
But you shouldn't need it. You are already using -t to specify the window, use it to specify the session as well:
tmux send-keys -t "$SESSION:8021" 'quit' C-m
You don't need select-window either unless you later plan to attach, and then one select-window at the end would do. See https://github.com/tmux/tmux/wiki/Advanced-Use#command-targets for a description of targets.
You may also find the has-session command useful instead of using grep, or the -F flag to list-sessions.
I am trying to find a nice way to restore the SSH agent when I reconnect a disconnected tmux session.
The cause seems to be that the SSH agent session changes but the environment variable from the tmux session is not updated.
How can I automate this, before attaching the session itself? Because the session I am attaching to does not always have a bash prompt, so I cannot afford to type something inside it. It has to be something to run before creating or attaching the tmux session.
An example of the code I'm running is at https://gist.github.com/ssbarnea/8646491 -- a small ssh wrapper that is using tmux to create persistem ssh connections. This works quite well, but sometimes the ssh agent stops working so I am no longer able to use it to connect to other hosts.
There's an excellent gist by Martijn Vermaat, which addresses your problem in great depth, although it is intended for screen users, so I'm adjusting it for tmux here.
To summarize:
create ~/.ssh/rc if it doesn't exist yet, and add the following content:
#!/bin/bash
# Fix SSH auth socket location so agent forwarding works with tmux.
if test "$SSH_AUTH_SOCK" ; then
ln -sf $SSH_AUTH_SOCK ~/.ssh/ssh_auth_sock
fi
Make it work in tmux, add this to your ~/.tmux.conf:
# fix ssh agent when tmux is detached
setenv -g SSH_AUTH_SOCK $HOME/.ssh/ssh_auth_sock
Extra work is required if you want to enable X11 forwarding, see the gist.
While tmux updates SSH variables by default, there is no need to
change/add socket path
change the SSH_AUTH_SOCKET variable
I like the solution by Chris Down which I changed to add function
fixssh() {
eval $(tmux show-env \
|sed -n 's/^\(SSH_[^=]*\)=\(.*\)/export \1="\2"/p')
}
into ~/.bashrc. Call fixssh after attaching session or before ssh/scp/rsync.
Newer versions of tmux support -s option for show-env, so only
eval $(tmux show-env -s |grep '^SSH_')
is possible.
Here's what I use for updating SSH_AUTH_SOCK inside a tmux window (based on Hans Ginzel's script):
alias fixssh='eval $(tmux showenv -s SSH_AUTH_SOCK)'
Or for tmux that does not have showenv -s:
alias fixssh='export $(tmux showenv SSH_AUTH_SOCK)'
Here is my solution which includes both approaches, and does not require extra typing when I reconnect to tmux session
alias ssh='[ -n "$TMUX" ] && eval $(tmux showenv -s SSH_AUTH_SOCK); /usr/bin/ssh'
There are lots of good answers here. But there are cases where tmux show-environment doesn't see SSH_AUTH_SOCK. In that case you can use find to locate it explicitly.
export SSH_AUTH_SOCK=$(find /tmp -path '*/ssh-*' -name 'agent*' -uid $(id -u) 2>/dev/null | tail -n1)
That's long and complicated, so I'll break it down...
01 export SSH_AUTH_SOCK=$(
02 find /tmp \
03 -path '*/ssh-*'
04 -name 'agent*'
05 -uid $(id -u)
06 2>/dev/null
07 | tail -n1
08 )
export the SSH_AUTH_SOCK environment variable set to the output of the $() command substitution
find files starting in /tmp
limit results to only those with /ssh- in the path
limit results to only those whose name begins with agent
limit results to only those with a user id matching the current user
silence all (permissions, etc.) errors
take only the last result if there are multiple
You may be able to leave off 6 & 7 if you know that there will only be 1 result and you don't care about stderr garbage.
I use a variation of the previous answers:
eval "export $(tmux show-environment -g SSH_AUTH_SOCK)"
assuming that you did the ssh agent started from the outer environment. Same goes for other environment variables such as DISPLAY.
I prefer to avoid configuring TMUX (etc) and keep everything purely in ~/.ssh/. On the remote system:
Create ~/.ssh/rc:
#!/bin/bash
# Fix SSH auth socket location so agent forwarding works within tmux
if test "$SSH_AUTH_SOCK" ; then
ln -sf $SSH_AUTH_SOCK ~/.ssh/ssh_auth_sock
fi
Add following to ~/.ssh/config so it no longer relies on $SSH_AUTH_SOCK, which goes stale in detached terminals:
Host *
IdentityAgent ~/.ssh/ssh_auth_sock
Known limitations
ssh-add doesn't use ~/.ssh/config and so cannot communicate with ssh-agent. Commands like ssh-add -l produce errors, even though ssh user#host works fine, as does updating git remotes which are accessed via SSH.
I may have worked out a solution that is fully encapsulated in the ~/.tmux.conf configuration file. It is a different approach than modifying the ~/.bash_profile and ~/.ssh/rc.
Solution only using ~/.tmux.conf
Just cut and paste the following code into your ~/.tmux.conf
# ~/.tmux.conf
# SSH agent forwarding
#
# Ensure that SSH-Agent forwarding will work when re-attaching to the tmux
# session from a different SSH connection (after a dropped connection).
# This code will run upon tmux create, tmux attach, or config reload.
#
# If there is an SSH_AUTH_SOCK originally defined:
# 1) Remove all SSH related env var names from update-environment.
# Without this, setenv cannot override variables such as SSH_AUTH_SOCK.
# Verify update-environment with: tmux show-option -g update-environment
# 2) Force-set SSH_AUTH_SOCK to be a known location
# /tmp/ssh_auth_sock_tmux
# 3) Force-create a link of the first found ssh-agent socket at the known location
if-shell '[ -n $SSH_AUTH_SOCK ]' " \
set-option -sg update-environment \"DISPLAY WINDOWID XAUTHORITY\"; \
setenv -g SSH_AUTH_SOCK /tmp/ssh_auth_sock_tmux; \
run-shell \"ln -sf $(find /tmp/ssh-* -type s -readable | head -n 1) /tmp/ssh_auth_sock_tmux\" \
"
Caveat
The above solution along with the other solutions are susceptible to a race condition when initiating multiple connections to the same machine. Consider this:
Client 1 Connect: SSH to machineX, start/attach tmux (writes ssh_auth_sock link)
Client 2 Connect: SSH to machineX, start/attach tmux (overwrites ssh_auth_sock link)
Client 2 Disconnect: Client 1 is left with a stale ssh_auth_sock link, thus breaking ssh-agent
However, this solution is slightly more resilient because it only overwrites the ssh_auth_sock link upon tmux start/attach, instead of upon initialization of a bash shell ~/.bash_profile or ssh connection ~/.ssh/rc
To cover this last race condition, one may add a key binding to reload the tmux configuration with a (Ctrl-b r) key sequence.
# ~/.tmux.conf
# reload config file
bind r source-file ~/.tmux.conf
From within an active tmux session, executing this sequence when the ssh_auth_sock link goes stale will refresh the ssh-agent connection.
In case other fish shell users are wondering how to deal with this when using fish (as well as for my future self!). In my fish_prompt I added a call to the following function:
function _update_tmux_ssh
if set -q TMUX
eval (tmux show-environment SSH_AUTH_SOCK | sed 's/\=/ /' | sed 's/^/set /')
end
end
I suppose that more advanced *nix users would know how to replace sed with something better, but this works (tmux 3.0, fish 3.1).
Following up on #pymkin's answer above, add the following, which worked with tmux 3.2a on macOS 11.5.3:
To ~/.tmux.conf:
# first, unset update-environment[SSH_AUTH_SOCK] (idx 3), to prevent
# the client overriding the global value
set-option -g -u update-environment[3]
# And set the global value to our static symlink'd path:
set-environment -g SSH_AUTH_SOCK $HOME/.ssh/ssh_auth_sock
To ~/.ssh/rc:
#!/bin/sh
# On SSH connection, create stable auth socket path for Tmux usage
if test "$SSH_AUTH_SOCK"; then
ln -sf "$SSH_AUTH_SOCK" ~/.ssh/ssh_auth_sock
fi
What's going on? Tmux has the semi-helpful update-environment variable/feature to pick up certain environment variables when a client connects. I.e. when you do tmux new or tmux attach, it'll update the tmux environment from when you ran those commands. That's nice for new shells or commands you run inside tmux afterwards, but it doesn't help those shells you've started prior to the latest attach. To solve this, you could use some of the other answers here to have existing shells pick up this updated environment, but that's not the route I chose.
Instead, we're setting a static value for SSH_AUTH_SOCK inside tmux, which will be ~/.ssh/ssh_auth_sock. All shells inside tmux would pick that up, and never have to be updated later. Then, we configure ssh so that, upon connection, it updates that static path with a symlink to the latest real socket that ssh knows.
The missing piece from #pymkin's answer is that Tmux will have the session value override the global value, so doing set-environment -g isn't sufficient; it gets squashed whenever you re-attach. You also have to also tell tmux not to update SSH_AUTH_SOCK in the session environment, so that the global value can make it through. That's what the set-option -g -u is about.
After coming across so many suggestions, I finally figured out a solution that enables TMUX update the stale ssh agent after being attached. Basically, both the zshrc files on the local and remote machines need to be modified.
Insert the following codes into the local zshrc, which is based on this reference.
export SSH_AUTH_SOCK=~/.ssh/ssh-agent.$(hostname).sock
ssh-add -l 2>/dev/null >/dev/null
# The error of executing ssh-add command denotes a valid agent does not
# exist.
if [ $? -ge 1 ]; then
# remove the socket if it exists
if [ -S "${SSH_AUTH_SOCK}" ]; then
rm "${SSH_AUTH_SOCK}"
fi
ssh-agent -a "${SSH_AUTH_SOCK}" >/dev/null
# one week life time
ssh-add -t 1W path-to-private-rsa-file
fi
Insert the following code into the remote zshrc, where the tmux session will be attached.
alias fixssh='eval $(tmux showenv -s SSH_AUTH_SOCK)'
Then ssh into the remote machine. The -A option is necessary.
ssh -A username#hostname
Attach the TMUX session. Check the TMUX evironment variables
# run this command in the shell
tmux showenv -s
# or run this command after prefix CTRL+A or CTRL+B
:show-environment
Run fixssh in the previously existed panes to update the ssh agent. If a new pane is created, it will automatically get the new ssh-agent.
Here's another simple Bash solution, using PROMPT_COMMAND to update the SSH_* vars inside tmux before each prompt is generated. The downside to this solution is that it doesn't take effect in existing shells until a new prompt is generated, because PROMPT_COMMAND is only run before creating new prompts.
Just add this to your ~/.bashrc:
update_tmux_env () {
# Only run for shells inside a tmux session.
if [[ -n "$TMUX" ]]; then
eval $(tmux show-env -s | grep '^SSH_')
fi
}
export PROMPT_COMMAND=update_tmux_env
Here's a new fix to an old problem: I think it's simpler than the other fixes and there's no need to make a static socket or mess with the shell prompt or make a separate command you have to remember to run.
I added this code added to my .bashrc file:
if [[ -n $TMUX ]]; then
_fix_ssh_agent_in_tmux () { if [[ ! -S $SSH_AUTH_SOCK ]]; then eval export $(tmux show-env | grep SSH_AUTH_SOCK); fi }
ssh () { _fix_ssh_agent_in_tmux; command ssh $#; }
scp () { _fix_ssh_agent_in_tmux; command scp $#; }
git () { _fix_ssh_agent_in_tmux; command git $#; }
rsync () { _fix_ssh_agent_in_tmux; command rsync $#; }
fi
If the shell is running within tmux, it redefines 'ssh' and its ilk to bash functions which test and fix SSH_AUTH_SOCK before actually running the real commands.
Note that tmux show-env -g also returns a value for SSH_AUTH_SOCK but that one is stale, I assume it's from whenever the tmux server started. The command above queries the current tmux session's environment which seems to be correct.
I'm using tmux 2.6 (ships with with Ubuntu 18.04) and it seems to work well.
I like to call :clear-history on panes with a huge scrollback. However, I want to script a way to send this command to all the panes in the various windows.
I know how to send a command to all the windows, courtesy of this question, but how do I send a command to all the panes of which window as well?
send-keys and synchronize-panes from the tmux manpage come to mind, but I'm not sure how to marry them together. But maybe there is a simpler way to do this.
Extra Observations:
Thinking about this a little bit, tmux list-panes -a seems to list all the panes in the current session. Pretty useful to start off with. Where do I go from here?
Have you tried following in tmux window with multiple panes
Ctrl-B :
setw synchronize-panes on
clear history
A bit late to the party but I didn't want to set and unset synchronize-panes just to send one command so I created a wrapper function around tmux and added a custom function called send-keys-all-panes.
_tmux_send_keys_all_panes_ () {
for _pane in $(tmux list-panes -F '#P'); do
tmux send-keys -t ${_pane} "$#"
done
}
I also create a wrapper around the tmux command to simplify calling this function (for convenience). The wrapper and the above code are all here.
This allows me to run tmux send-keys-all-panes <command> or tmux skap <command to send <command> to all panes.
Note that tmux is aliased to my wrapper function tmux_pp.
Update June 2019
Quick illustration on how to configure your own binding for synchronize panes.
Added the following into my tmux.conf (the comments certainly apply to my overall configuration):
# synchronize all panes in a window
# don't use control S, too easily confused
# with navigation key sequences in tmux (show sessions)
unbind C-S
bind C-Y set-window-option synchronize-panes
Now, I can toggle the ability to synchronize commands across multiple panes with <C-a><C-y>.
(Yes, I remapped the bind key to Ctrl a).
my tmux version is 1.9a, and this works for me, one key is enough for both on and off
bind-key X set-window-option synchronize-panes\; display-message "synchronize-panes is now #{?pane_synchronized,on,off}"
None of the above answers worked for me (tmux v2.3), but this did, from the bash command line:
for _pane in $(tmux list-panes -a -F '#{pane_id}'); do \
tmux clear-history -t ${_pane} ; done
A more generalized script, for tmux commands other than 'clear-history' would just replace that element with a parameter, eg. $1. Do be careful if you intend to write a script to handle a series of tmux commands, as "-t ${_pane}" will need to be applied to each.
Note that the -a parameter to tmux list-panes is required to cover all panes in all windows in all sessions. Without that, only panes in your current tmux window will be affected. If you have more than one tmux session open and only want to apply the command to panes within the current session, replace -a with -s (It's all in the tmux man page).
I haven't the mod points to comment directly on each of the above answers, so here's why they weren't working for me:
The problem that I had with #shailesh-garg 's answer was that the sync affected only commands issued within the panes, not tmux commands issued using Ctrl-B : which are outside the panes.
The three problems that I had with #kshenoy 's answer were that:
it sends keystrokes to within a pane, not to the tmux operation
of that pane, so for instance, if one had a bash shell running in
the pane and one used the script to send "clear-history", those
would be the keystrokes that would appear in the bash command-line.
A work-around would be to send "tmux clear-history" or to pre-pend
"tmux " to "$#", but I haven't edited the answer because of my other
problems with the answer;
I couldn't figure out how to send a
new-line character without literally breaking the line;
Even when I did that, sending "tmux clear-history" had no effect.
If you want to send your command to every pane in every window in every session, add this to your .bashrc:
send_command_to_every_pane() {
for session in `tmux list-sessions -F '#S'`; do
for window in `tmux list-windows -t $session -F '#P' | sort`; do
for pane in `tmux list-panes -t $session:$window -F '#P' | sort`; do
tmux send-keys -t "$session:$window.$pane" "$*" C-m
done
done
done
}
You can then use it like this:
send_command_to_every_pane source ~/.bash_profile
Change "$*" to "$#" if you want that behavior, but in my experience this is what you want.
tmux send-keys -t <session id> <command> C-m
Replace the "session id" and "command" accordingly.
This is my utility function to do it, only executing the command when there there is nothing running in the pane.
#!/bin/bash
_send_bash_command_to_session() {
if [[ $# -eq 0 || "$1" = "--help" ]] ; then
echo 'Usage: _send_bash_command_to_session $session_name what ever command you want: '
return
fi
input_session="$1"
input_command="${#:2}"
for _pane in $(tmux list-panes -s -t ${input_session} -F '#{window_index}.#{pane_index}'); do
# only apply the command in bash or zsh panes.
_current_command=$(tmux display-message -p -t ${input_session}:${_pane} '#{pane_current_command}')
if [ ${_current_command} = zsh ] || [ ${_current_command} = bash ] ; then
tmux send-keys -t ${_pane} "${input_command}" Enter
fi
done
}
tmux_set_venv() {
_current_session=$(tmux display-message -p '#{session_name}')
_send_bash_command_to_session ${_current_session} workon $1
}
Example targeting a session called dev, enabling a python virtualenv in all panes that are in bash or zsh, avoiding executing the command in panes with vim or any other executable:
_send_bash_command_to_session dev workon myvirtualenv
or easier to remember: to do it in the current session:
tmux_set_venv myvirtualenv
Find my configuration file with this function.
You can combine synchronize-panes and send-keys in a single shortcut to send commands to all the panes:
Predefined tmux command clear-history:
bind-key C set-option -w synchronize-panes on\; clear-history \; set-option -w synchronize-panes off
Prompt an arbitrary tmux command:
bind-key p command-prompt -p "Panes command: " "set-option -w synchronize-panes on; %% ; set-option -w -u synchronize-panes"
Prompt an arbitrary shell command:
bind-key p command-prompt -p "Panes command: " "set-option -w synchronize-panes on; send-keys %%\\n ; set-option -w -u synchronize-panes"
By default, byobu uses tmux as backend. It's a wrapper that make things much easier:
Shift+F9:
Ctrl+F9:
Shift+F1
Admittedly only semi-related, I found I could make the status background red when I toggle synchronize-panes so it's obvious when I switch back to a window with an unknown synchronize-panes state:
bind-key C-x setw synchronize-panes on \; set-window-option status-bg red \; display-message "pane sync on"
bind-key M-x setw synchronize-panes off \; set-window-option status-bg default \; display-message "pane sync off"
I wonder is there any easy way that I can change an bash environment variable and apply to windows in a tmux session?
I've googled and didn't found a solution so I post the question here.
Thanks!!
You can't directly change the environment variables.
However, you can make shell terminals inside a tmux instance pick up new variables. This requires a few steps.
First, tmux can update environment variables in itself. The update-environment configuration directive does this. Any variable listed here will be auto-udpated - connecting to a tmux session updates the session's environment variable with the value from the client you just connected. So if you run tmux attach, and have SSH_AUTH_SOCK set, then the tmux session will get the new value of SSH_AUTH_SOCK.
However, that only updates the session's variables, so only new panes/windows will get the values. Existing windows will still have the old values. As #IgnacioVazquez-Abrams said, there is not a direct fix to this.
However, you can fix it in many programs. Sufficiently recent versions of tmux have a show-environment command, which queries the session for the current values of an environment variable. This allows you to get the environment variable from within a program after it has been with the update-environment logic.
For instance, you can have some shells pick up the new value. In ZSH, I do this with a precmd hook in ~/.zshrc:
_update_ssh_agent() {
local var
var=$(tmux show-environment |grep '^SSH_AUTH_SOCK=')
if [ "$?" -eq 0 ]; then
eval "$var"
fi
}
if [[ -n "$TMUX" ]]; then
add-zsh-hook precmd _update_ssh_agent
fi
This makes it so that shells inside tmux sessions update the SSH agent every time they go to display a new prompt. After I reconnect, all I have to do is hit enter at a prompt and it grabs the new SSH agent connection.
Bash also has a pre-command mechanism, although I do not know how to configure it off-hand. You could additionally configure more programs to use show-environment to update themselves, such as vim or emacs. However, you will need to configure each program you might want to do this with separately.
No.
And there isn't even a hard way; manipulating the environment variables of another process is non-portable at best.
So this is an old question, but came up when I was searching for what I wanted to do, so here's another solution.
When tmux is started, it copies the environment into a global environment. When new windows are created, it merges the global environment with the session environment to set the environment for that window. We can view these environments with:
tmux show-environment [-g] [-t target-session]
Even better, we can also update the environments, even from within the windows' own tmux session:
tmux set-environment [-gru] [-t target-session] name [value]
For a full explanation of the flags, see the tmux man page.
This feature was exactly what I wanted. Unfortunately it won't update the environment of existing shells, but we could easily loop over tmux showenv -g to re-export the tmux environment that might be set by another process.
Here was my use-case:
With the way I have my shell configuration set up, I export my environment in a login shell, and then exec into a tmux session. I figure since env vars don't change often, I don't need to source them in new non-login shells every time. However, when they do change, I don't want to restart my entire tmux session to have new tmux windows know about the change. While using the update-environment option and re-attaching solves a session restart, it's cumbersome to maintain an explicit list of potentially malleable env vars in my tmux configuration.
With the following function, we can update our environment variables in something like ~/.shenv for example, and instead of sourcing the file (. ~/.shenv), we can promote the file (promote ~/.shenv) for new tmux windows to inherit from this updated environment.
promote() {
sourced="$1"; shift
. "$sourced"
env - \
"HOME=$HOME" \
sh -c ". $sourced; env" | cut -d= -f1 | while read -r var; do
val="$(eval "echo \"\$$var\"")"
tmux set-environment -gt local "$var" "$val"
done
}
What's happening here is we're sourcing our file from within a shell with an empty environment (apart from the HOME we add), and print out our new env vars. We pipe those into a cut to extract the variable of each line, storing it in a variable called var. After some meta magic with eval to get the indirect value of that variable from the current shell, we update our tmux target session. In this case, local is the name of our tmux session.
After wrestling with different solutions, I came up with this bash function added to my .bashrc file:
if [[ -n $TMUX ]]; then
_fix_ssh_agent_in_tmux () { if [[ ! -S $SSH_AUTH_SOCK ]]; then eval export $(tmux show-env | grep SSH_AUTH_SOCK); fi }
ssh () { _fix_ssh_agent_in_tmux; command ssh $#; }
scp () { _fix_ssh_agent_in_tmux; command scp $#; }
rsync () { _fix_ssh_agent_in_tmux; command rsync $#; }
fi
If the shell is running within tmux, it redefines 'ssh' to a bash function that tests and fixes SSH_AUTH_SOCK before actually running the real ssh command.
Note that tmux show-env -g also returns a value for SSH_AUTH_SOCK but that one is stale, I assume it's from whenever the tmux server started. The command above queries the current tmux session' environment which seems to be correct.
I'm using tmux 2.6 (ships with with Ubuntu 18.04) and it seems to work well.
I am trying to figure out how to attach to a tmux session if a named tmux session exists, if not I want to create a new one with the given name.
Currently, I know of a few tmux commands which can partly achieve what I am looking for, but its not clear how to combine them together to get what I am looking for:
tmux attach attaches to an automatically existing session - but errors out if no session exists
tmux new creates a new session - but it does so every time, so I can't leave it in my .tmux.conf
tmux has-session tests whether a session exists - but I don't know how to stitch it together with the other commands
Thus, I would like to create a tmux script, so that this happens automatically, instead of having to manually create it everytime I need to log into a sessions.
How can I write a automatic script so as to create a new tmux session (if a given session name doesnt exist) or attach to a session name (if it exists)?
I figured it out (and had it pointed out to me).
tmux attach || tmux new
Alternately, you can add
new-session
to your .tmux.conf - that will create a default session on server start.
Then tmux attach will either attach to the current session (running server, that is), or create a new session (start the server, read the config file, issue the new-session command) and attach to that.
As pointed out in comments from Petr Viktorin, jkoelker and pjincz, you can use the following command to attach to mySession if it exists, and to create it if it doesn't:
tmux new -A -s mySession
From man tmux:
new-session[-AdDEP] [-cstart-directory] [-Fformat] [-nwindow-name] [-ssession-name] [-tgroup-name] [-xwidth] [-yheight] [shell-command]
(alias: new)
Create a new session with name session-name.
[...]
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.
new-session has supported -A since tmux-1.8.
Adapting Alex's suggestion to include project based configuration upon startup, I started using the following:
# ~/bin/tmux-myproject shell script
# The Project name is also used as a session name (usually shorter)
PROJECT_NAME="myproject"
PROJECT_DIR="~/myproject"
tmux has-session -t $PROJECT_NAME 2>/dev/null
if [ "$?" -eq 1 ] ; then
echo "No Session found. Creating and configuring."
pushd $PROJECT_DIR
tmux new-session -d -s $PROJECT_NAME
tmux source-file ~/bin/tmux-${PROJECT_NAME}.conf
popd
else
echo "Session found. Connecting."
fi
tmux attach-session -t $PROJECT_NAME
where tmux-myproject.conf is my startup series of tmux commands to create my windows and panes, as well as start my editors.
Although I find rampion's answer is sufficient for using 1 session, this script lets you setup multiple sessions:
SESSIONS="work play"
function has-session {
tmux has-session -t $1 2>/dev/null
}
function except
{
if [ "$?" -eq 1 ] ; then
$1
fi
}
# Configure your sessions here
function session-work
{
tmux new-session -d -s work
tmux neww -k -t work:1
}
function session-play
{
tmux new-session -d -s play
tmux neww -k -t play:1
}
#
#MAIN
for x in $SESSIONS
do
echo $x
has-session $x
except session-$x
done
NOTE:
-k --> new-window will not be created if already exists
-d --> start session or window, but don't attach to it yet
-s --> name the session
-t --> specify a target location in the form session:window.pane
I use an alias to create a new session if needed, and attach to my default session if it already exists:
alias tmuxre='tmux new-session -t default || tmux new-session -s default'
I added this to my .login on my server.
The reason I do it this way is because I don't want to attach to the same actual session, I want a new session which uses the same group of windows.
This is also similar to running screen -xRR.
For those who want to do the same thing in fish:
tmux attach -t mysesh; or tmux new -s mysesh
(edit: A solution considering named sessions is mentioned at the end of this answer)
I came across this question when I was looking for a particular use-case, but couldn't find any solutions to it, so I'll add mine here:
Upon terminal-launch tmux should:
check whether there are any unattached sessions and use the first it can find (each session will be attached only once)
if there are no unattached sessions create a new one
After reading through the tmux man-pages and looking up arrays in bash I was able to come up with the following one-liner:
tmux attach -t ${$(tmux list-sessions -F '#{session_name}' -f '#{==:#{session_attached},0}')[1]} || tmux new
Explanation:
tmux attach -t $A:
attach to session with content of variable A (in our case the return value of the list-session command + array-index call)
tmux new:
create new session
together -> tmux attach -t $A || tmux new:
if tmux attach fails, create a new session
The next part (our $A) is finding an unattached session:
A = ${$B[1]}: return the second element in the list B (first one seems to always be an empty string)
B = tmux list-sessions -F '#{session_name}' -f '#{==:#{session_attached},0}'
tmux list-sessions: list all sessions
tmux list-sessions -F '#{session_name}: -F stands for format and -F '#{session_name}' tells tmux to only show the name of the session and nothing else when it outputs the list
tmux list-sessions -f '#{==:#{session_attached},0}': -f stands for filter and -f '#{==:#{session_attached},0}'tells tmux to show only those list-elements, where the session_attached-value is equal to 0
tmux list-sessions -F '#{session_name}' -f '#{==:#{session_attached},0}': both flags in combination will output only the session name and only for those elements of the list, where the session_attached-value is equal to 0 (=unattached sessions)
Example:
My application was for WSL, so I added it to the launch of my Ubuntu profile inside the settings.json of Windows Terminal:
"commandline": "C:\\Windows\\system32\\wsl.exe -d Ubuntu-22.04 tmux attach -t ${$(tmux list-sessions -F '#{session_name}' -f '#{==:#{session_attached},0}')[1]} || tmux new",
Edit:
If you have ([a-zA-Z]) named sessions you can sort the list to put those at the beginning:
tmux attach -t ${$(sort -n <<<"${$(tmux list-sessions -F '#{session_name}' -f '#{==:#{session_attached},0}')[*]}")[1]} || tmux new
If you add tmux new -s "primary" || at the beginning of the previous command it will try to create the session with the name "primary" and if it already exists it will only attach to it if it is still unattached, otherwise it will take another unattached session (prioritizing named over unnamed) or just create a new unnamed session if there are no unattached sessions left.
Caveat: each time you run this command and "primary" already exists it will output an error-message that it wasn't able to create a session called "primary" (only visible for a split second)
edit edit:
you can redirect those messages by using &> /dev/null:
(tmux new -s primary || tmux new -s secondary || tmux new -s tertiary) &> /dev/null || tmux attach -t ${$(sort -n <<<"${$(tmux list-sessions -F '#{session_name}' -f '#{==:#{session_attached},0}')[*]}")[1]} || tmux new"