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iandol
Dec 23, 2025

This is a follow on from #995. I use conda-forge via pixi to install my packages cross-platform. With tmux V3.6a and tmuxp V1.62 I get a crash when I try to start.

  1. Run a new single tmux session: tmux new-session -s test
  2. Run tmuxp freeze to save it to test.yaml.
  3. Shut down tmux. (and tmux kill-server it just to be sure).
  4. Edit test.yaml to remove the layout.
  5. tmuxp load test
➪ cat .config/tmuxp/test.yaml
   1 session_name: test
   2 windows:
   3 - focus: 'true'
   4   options: {}
   5   panes:
   6   - focus: 'true'
   7     shell_command: elvish
   8   start_directory: /home/cog5
   9   window_name: elvish
                            
➪ tmuxp load test
[Loading] /home/cog5/.config/tmuxp/test.yaml
Traceback (most recent call last):
                                    File "/home/cog5/.pixi/envs/tmuxp/bin/tmuxp", line 9, in <module>
                                                                                                         sys.exit(cli.cli())
                                                                                                                                         ~~~~~~~^^
                                                                                                                                                    File "/home/cog5/.pixi/envs/tmuxp/lib/python3.14/site-packages/tmuxp/cli/__init__.py", line 148, in cli
                                                                 command_load(
                                                                                  ~~~~~~~~~~~~^
                                                                                                       args=CLILoadNamespace(**vars(args)),
                                                                                                                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                                                                                                                                                                                               parser=parser,
                       ^^^^^^^^^^^^^^
                                         )
                                              ^
                                                 File "/home/cog5/.pixi/envs/tmuxp/lib/python3.14/site-packages/tmuxp/cli/load.py", line 562, in command_load
                                                                                                                                                                 load_workspace(
                                                                                                                                                                                    ~~~~~~~~~~~~~~^
             workspace_file,
                                    ^^^^^^^^^^^^^^^
                                                       ...<2 lines>...
                                                                              **tmux_options,
                                                                                                     ^^^^^^^^^^^^^^^
                                                                                                                        )
                                                                                                                             ^
                                                                                                                                File "/home/cog5/.pixi/envs/tmuxp/lib/python3.14/site-packages/tmuxp/cli/load.py", line 372, in load_workspace
                                                    _load_attached(builder, detached)
                                                                                         ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
                                                                                                                            File "/home/cog5/.pixi/envs/tmuxp/lib/python3.14/site-packages/tmuxp/cli/load.py", line 152, in _load_attached
                                                builder.session.attach()
                                                                            ~~~~~~~~~~~~~~~~~~~~~~^^
                                                                                                      File "/home/cog5/.pixi/envs/tmuxp/lib/python3.14/site-packages/libtmux/session.py", line 330, in attach
                   raise exc.LibTmuxException(proc.stderr)
                                                          libtmux.exc.LibTmuxException: ['server exited unexpectedly']
                                                                                                                      Exception: tmuxp exited with 1

tmuxp debug-info

➪ tmuxp debug-info
-------------------------
environment:
	dist: Linux-6.14.0-37-generic-x86_64-with-glibc2.39
	arch: x86_64
	uname: Linux; cog5; 6.14.0-37-generic
	version: #37~24.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Nov 20 10:25:38 UTC 2
-------------------------
python version: 3.14.2 | packaged by conda-forge | (main, Dec  6 2025, 11:21:58) [GCC 14.3.0]
system PATH: /home/cog5/.pixi/envs/tmuxp/bin:/home/cog5/bin:/home/cog5/.pixi/bin:/home/cog5/.npm/bin:/home/cog5/.x-cmd.root/local/data/pkg/sphere/X/l/j/h/bin:/home/cog5/.config/carapace/bin:/home/linuxbrew/.linuxbrew/sbin:/home/linuxbrew/.linuxbrew/bin:/home/cog5/.x-cmd.root/bin:/home/cog5/.pixi/envs/ruby/share/rubygems/bin:/home/cog5/.local/bin:/usr/local/sbin:/usr/local/bin:/home/cog5/.cache/lm-studio/bin:/opt/amdgpu-pro/bin:/home/cog5/.TinyTeX/bin/x86_64-linux:/usr/local/MATLAB/R2025b/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/cog5/.local/share/kitty-ssh-kitten/kitty/bin
tmux version: 3.6
libtmux version: 0.53.0
tmuxp version: 1.62.0
tmux path: /home/cog5/.pixi/envs/tmuxp/bin/tmux
tmuxp path: /home/cog5/.pixi/envs/tmuxp/lib/python3.14/site-packages/tmuxp
shell: /usr/bin/zsh
-------------------------
tmux sessions:


	no server running on /tmp/tmux-1000/default

tmux windows:


	no server running on /tmp/tmux-1000/default

tmux panes:


	no server running on /tmp/tmux-1000/default

tmux global options:


	no server running on /tmp/tmux-1000/default

tmux window options:


	no server running on /tmp/tmux-1000/default

tmux version and install method (pixi / system / pacman / brew / pip)

V3.6a via pixi (conda-forge)

├── tmux: 3.6a 
│   └─ exposes: tmux
├── tmuxp: 1.62.0 
│   └─ exposes: tmuxp

your tmux config (or confirmation it’s empty)

https://codeberg.org/iandol/dotfiles/src/branch/main/tools/tmux.conf

confirmation that no tmux processes are running (ps -ef | grep '[t]mux')

I did a tmux kill-server, pkill tmux and then procs | grep tmux

whether tmux new -s test works reliably before invoking tmuxp

I get an error:

tmux new -s
no server running on /tmp/tmux-1000/default

but tmux new-session works.

Additionally:

Try the tmuxp configuration without the layout, to rule out layout parsing or geometry issues
Check whether tmux produced a core dump and, if so, inspect it

where can I find the core dump? Thank you for your help and patience.
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Replies: 2 comments

Comment options

tony
Jan 12, 2026
Maintainer

@iandol I’m not convinced yet this is a tmuxp bug.

With tmux fully stopped, if you run:

tmuxp load -f /dev/null <config_file>

does it still crash?

Reasoning: this forces tmux to start with an empty configuration, bypassing any tmux.conf, TPM plugins, or option side effects. If the crash disappears under -f /dev/null, that strongly suggests a tmux 3.6a + config interaction rather than tmuxp’s session builder.
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HalJordan
Apr 10, 2026

I just started getting this myself:

user@theseus ~ % cat scratch.txt 
ValueError: zip() argument 2 is shorter than argument 1

    sys.exit(cli.cli())


user@theseus ~ % tmuxp load -f /dev/null .config/tmuxp/Local.yaml 
Traceback (most recent call last):
  File "/usr/bin/tmuxp", line 8, in <module>
    sys.exit(cli.cli())
             ~~~~~~~^^
  File "/usr/lib/python3.14/site-packages/tmuxp/cli/__init__.py", line 306, in cli
    command_load(
    ~~~~~~~~~~~~^
        args=CLILoadNamespace(**vars(args)),
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        parser=parser,
        ^^^^^^^^^^^^^^
    )
    ^
  File "/usr/lib/python3.14/site-packages/tmuxp/cli/load.py", line 893, in command_load
    load_workspace(
    ~~~~~~~~~~~~~~^
        workspace_file,
        ^^^^^^^^^^^^^^^
    ...<11 lines>...
        no_progress=args.no_progress,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/lib/python3.14/site-packages/tmuxp/cli/load.py", line 582, in load_workspace
    builder = WorkspaceBuilder(
        session_config=expanded_workspace,
        plugins=load_plugins(expanded_workspace, colors=cli_colors),
        server=t,
    )
  File "/usr/lib/python3.14/site-packages/tmuxp/workspace/builder.py", line 377, in __init__
    session_name=self.session_config["session_name"],
                 ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
KeyError: 'session_name'
1 user@theseus ~ % cat .config/tmuxp/Local.yaml
Session_name: Local
windows:
- window_name: Local
user@theseus ~ %
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