zmx

Session attach/detach for the terminal.
Docs · You might not need tmux · Sponsored by pico.sh

features

• Persist terminal shell sessions
• Ability to attach and detach from a shell session without it being killed
• Native terminal scrollback
• Multiple clients can connect to the same session
• Re-attaching to a session restores previous terminal state and output
• Send commands to a session without attaching to it
• Print scrollback history of a terminal session in plain text
• Works on mac and linux
• This project does NOT provide windows, tabs, or splits

demos

• zmx - intro
• zmx - ai portal

install

binaries

• https://zmx.sh/a/zmx-0.8.1-linux-aarch64.tar.gz
• https://zmx.sh/a/zmx-0.8.1-linux-x86_64.tar.gz
• https://zmx.sh/a/zmx-0.8.1-macos-aarch64.tar.gz
• https://zmx.sh/a/zmx-0.8.1-macos-x86_64.tar.gz

homebrew

brew install neurosnap/tap/zmx

mise-en-place

mise use zmx

NixOS / nixpkgs

Run immediately without installation:

nix run github:NixOS/nixpkgs/nixpkgs-unstable#zmx
# or build main yourself
nix run github:neurosnap/zmx

Start a shell with zmx available while it runs:

nix shell github:NixOS/nixpkgs/nixpkgs-unstable#zmx
# or built main yourself
nix run github:neurosnap/zmx

packages (unofficial)

• Alpine Linux
• Arch AUR tracking releases
• Arch AUR tracking git
• openSUSE Tumbleweed
• Gentoo (overlay)
• zmx-rpm packaging

src

• Requires zig v0.16
• Clone the repo
• Run build cmd

Be sure to add ~/.local/bin to your PATH:

zig build -Doptimize=ReleaseSafe --prefix ~/.local

usage

[!IMPORTANT] We recommend closing the terminal window to detach from the session but you can also press ctrl+\ or run zmx detach. If you need ctrl+\ for something else (e.g. vim's ctrl+\ ctrl+n to escape its own :terminal), set ZMX_NO_DETACH_KEY to disable the shortcut and rely on zmx detach or closing the window instead.

Run zmx help for more information on usage, with examples.

Usage: zmx <command> [args...]

Commands:
  [a]ttach <name> [command...]             Attach to session, creating if needed
  [r]un <name> [-d] [command...]           Send command without attaching
  [s]end <name> <text...>                  Send raw input to session PTY
  [p]rint <name> <text...>                 Inject text into session display
  [wr]ite <name> <file_path>               Write stdin to file_path through the session
  [d]etach                                 Detach all clients (ctrl+\\ for current client)
  [l]ist|ls [--short]                      List active sessions
  [g]et <name>                             Get session labels
  set <name> k=v ...                       Set session labels
  [cl]ear <name>                           Clear all session labels
  print-env [-s] <name> [key]              Print tracked environment variables
  [k]ill <name>... [--force]               Kill session and all attached clients
  [hi]story <name> [--vt|--html]           Output session scrollback
  [w]ait <name>...                         Wait for session tasks to complete
  [t]ail <name>...                         Follow session output
  [c]ompletions <shell>                    Shell completions (bash, zsh, fish, nu, yash)
  [v]ersion                                Show version and metadata (socket dir, log dir)
  [h]elp                                   Show this help

nested sessions

Nested sessions are not supported. Inside a session ZMX_SESSION is set, and attach reads it: instead of creating another client it switches the calling terminal to the session you named.

That matters when the variable is inherited rather than chosen. A script, build tool, or coding agent started inside a session runs with ZMX_SESSION set, so zmx attach other from there moves the terminal somebody was using, and the session it was showing is left with no client.

Unset it in anything that attaches on its own behalf:

env -u ZMX_SESSION zmx attach other

For non-interactive work prefer zmx run, which never switches the caller.

shell prompt

When you attach to a zmx session, we don't provide any indication that you are inside zmx. We do provide an environment variable ZMX_SESSION which contains the session name.

We recommend checking for that env var inside your prompt and displaying some indication there.

fish

Place this file in ~/.config/fish/config.fish:

functions -c fish_prompt _original_fish_prompt 2>/dev/null

function fish_prompt --description 'Write out the prompt'
  if set -q ZMX_SESSION
    echo -n "[$ZMX_SESSION] "
  end
  _original_fish_prompt
end

bash and zsh

Depending on the shell, place this in either .bashrc or .zshrc:

if [[ -n $ZMX_SESSION ]]; then
  export PS1="[$ZMX_SESSION] ${PS1}"
fi

powerlevel10k zsh theme

powerlevel10k is a theme for zsh that overwrites the default prompt statusline.

Place this in .zshrc:

function prompt_my_zmx_session() {
  if [[ -n $ZMX_SESSION ]]; then
    p10k segment -b '%k' -f '%f' -t "[$ZMX_SESSION]"
  fi
}
POWERLEVEL9K_RIGHT_PROMPT_ELEMENTS+=my_zmx_session

oh-my-posh

oh-my-posh is a popular shell themeing and prompt engine. This code will display an icon and session name as part of the prompt if (and only if) you have zmx active:

[[blocks.segments]]
   template = '{{ if .Env.ZMX_SESSION }} {{ .Env.ZMX_SESSION }}{{ end }}'
   foreground = 'p:orange'
   background = 'p:black'
   type = 'text'
   style = 'plain'

Starship

Starship is a popular shell themeing and prompt engine. This code will display an icon and session name as part of the prompt if (and only if) you have zmx active:

format = """
${env_var.ZMX_SESSION}\
...
"""

[env_var.ZMX_SESSION]
symbol = " "
format = "[$symbol$env_value]($style) "
description = "zmx session name"
style = "bold magenta"

environment variables

A session's environment is initialized when the session is created. When re-attaching from a new terminal or a different SSH connection, environment variables describing the client connection (such as SSH_AUTH_SOCK, DISPLAY, or terminal remote control variables like KITTY_LISTEN_ON, KITTY_PID, KITTY_WINDOW_ID) become outdated in the running shell.

zmx tracks these environment variables from attaching clients. You can inspect the current leader client's environment with zmx print-env:

# Print all tracked environment variables (set variables as KEY=VALUE, unset as -KEY)
zmx print-env .
zmx print-env dev

# Print POSIX shell commands (export ... / unset ...) suitable for eval
zmx print-env -s .

# Print a specific variable value
zmx print-env . SSH_AUTH_SOCK

You can automatically update your shell environment before each prompt:

bash

Add to ~/.bashrc:

_zmx_env_hook() {
  if [[ -n $ZMX_SESSION ]]; then
    eval "$(zmx print-env -s .)"
  fi
}
PROMPT_COMMAND="_zmx_env_hook${PROMPT_COMMAND:+; $PROMPT_COMMAND}"

zsh

Add to ~/.zshrc:

precmd() {
  if [[ -n $ZMX_SESSION ]]; then
    eval "$(zmx print-env -s .)"
  fi
}

fish

Add to ~/.config/fish/config.fish:

function _zmx_env_hook --on-event fish_prompt
  if test -n "$ZMX_SESSION"
    for line in (zmx print-env .)
      if string match -q -- "-*" $line
        set -e (string sub -s 2 $line)
      else
        set -gx (string split -m 1 "=" $line)
      end
    end
  end
end

configuring tracked variables

By default, zmx tracks:

• DISPLAY
• SSH_AUTH_SOCK
• SSH_AGENT_PID
• SSH_CONNECTION
• WINDOWID
• XAUTHORITY
• KITTY_LISTEN_ON
• KITTY_PID
• KITTY_WINDOW_ID

You can customize this list by setting ZMX_TRACK_ENV to a comma-separated list of variable names:

export ZMX_TRACK_ENV="DISPLAY,SSH_AUTH_SOCK,GPG_AGENT_INFO"

shell completion

Shell auto-completion for zmx commands and session names can be enabled using the completions subcommand. Once configured, you'll get auto-complete for both local zmx commands and sessions:

ssh remote-server zmx attach session-na<TAB>
# <- auto-complete suggestions appear here

NOTICE: when installing zmx with homebrew completions are automatically installed.

bash

Add this to your .bashrc file:

if command -v zmx &> /dev/null; then
  eval "$(zmx completions bash)"
fi

zsh

Add this to your .zshrc file:

if command -v zmx &> /dev/null; then
  eval "$(zmx completions zsh)"
fi

fish

Add this to ~/.config/fish/completions/zmx.fish:

if type -q zmx
  zmx completions fish | source
end

yash

Add this to your ~/.config/yash/rc:

if command -v zmx > /dev/null 2>&1; then
  eval "$(zmx completions yash)"
fi

Or save as an autoloaded script in your completion directory:

zmx completions yash > ~/.config/yash/completion/zmx

nu

Add this to your Nushell config (config.nu):

use ("~/.cache/zmx/completions.nu" | path expand)
# Or generate dynamically:
zmx completions nu | save -f ~/.cache/zmx/completions.nu

session picker

You can add an interactive session picker to your shell that lets you fuzzy-find existing sessions, preview their scrollback history, or create new ones -- all from a single prompt. This is especially useful for remote SSH workflows: add it to your shell startup so that connecting to a machine immediately presents the picker.

Requires fzf.

• Enter selects a matched session (or creates one if no sessions exist)
• Ctrl-N creates a new session using the typed query, even when a fuzzy match is highlighted

zmx-select() {
  local display
  local prefix="${ZMX_SESSION_PREFIX:-}"
  display=$(zmx list 2>/dev/null | while IFS=$'\t' read -r name pid clients created dir; do
    name=${name#*name=}
    pid=${pid#*pid=}
    clients=${clients#*clients=}
    dir=${dir#*start_dir=}
    if [[ -n "$prefix" ]]; then
      [[ "$name" == "$prefix"* ]] || continue
      name=${name#"$prefix"}
    fi
    printf "%-20s  pid:%-8s  clients:%-2s  %s\n" "$name" "$pid" "$clients" "$dir"
  done)

  local output query key selected session_name
  output=$({ [[ -n "$display" ]] && echo "$display"; } | fzf \
    --print-query \
    --expect=ctrl-n \
    --height=80% \
    --reverse \
    --prompt="zmx> " \
    --header="Enter: select | Ctrl-N: create new" \
    --preview='zmx history {1}' \
    --preview-window=right:60%:follow \
  )
  local rc=$?

  query=$(echo "$output" | sed -n '1p')
  key=$(echo "$output" | sed -n '2p')
  selected=$(echo "$output" | sed -n '3p')

  if [[ "$key" == "ctrl-n" && -n "$query" ]]; then
    session_name="$query"
  elif [[ $rc -eq 0 && -n "$selected" ]]; then
    session_name=$(echo "$selected" | awk '{print $1}')
  elif [[ -n "$query" ]]; then
    session_name="$query"
  else
    return 130
  fi

  zmx attach "$session_name"
}

if command -v zmx &> /dev/null && command -v fzf &> /dev/null && [[ -z "$ZMX_SESSION" ]]; then
  zmx-select && exit
fi

if command -v zmx &> /dev/null && [[ -z "$ZMX_SESSION" ]]; then
  local count
  count=$(zmx ls --short 2>/dev/null | wc -l)
  if [[ "$count" -gt 0 ]]; then
    echo "zmx: $count session(s) active — \`zmx-select\` to attach" >&2
  fi
fi

session prefix

We allow users to set an environment variable ZMX_SESSION_PREFIX which will prefix the name of the session for all commands. This means if that variable is set, every command that accepts a session will be prefixed with it.

export ZMX_SESSION_PREFIX="d."
zmx a runner # ZMX_SESSION=d.runner
zmx a tests  # ZMX_SESSION=d.tests
zmx k tests  # kills d.tests
zmx wait     # suspends until all tasks prefixed with "d." are complete

philosophy

The entire argument for zmx instead of something like tmux that has windows, panes, splits, etc. is that job should be handled by your os window manager. By using something like tmux you now have redundant functionality in your dev stack: a window manager for your os and a window manager for your terminal. Further, in order to use modern terminal features, your terminal emulator and tmux need to have support for them. This holds back the terminal enthusiast community and feature development.

Instead, this tool specifically focuses on session persistence and defers window management to your os wm.

ssh workflow

Try it out quickly

If you'd like to try out zmx and ssh without fiddling your ssh config, make sure to pass the -t option to ssh. Here's an example:

ssh -t dev-box zmx attach default

Without -t, the remote shell will not know it's talking to a terminal, and the display will likely get messed up.

This option isn't needed if you follow the configuration steps below, because RequestTTY yes does the same thing.

Configure it for regular use

Using zmx with ssh is a first-class citizen. Instead of using ssh to remote into your system with a single terminal and n tmux panes, you open n terminals and run ssh for all of them. This might sound tedious, but there are tools to make this a delightful workflow.

First, create an ssh config entry for your remote dev server:

Host = d.*
    HostName 192.168.1.xxx

    RemoteCommand zmx attach %k
    RequestTTY yes
    ControlPath ~/.ssh/cm-%r@%h:%p
    ControlMaster auto
    ControlPersist 10m

Architecturally, ssh supports multiplexing multiple channels of communication within a single connection to a server. ControlMaster is the setting that tells ssh to multiplex multiple PTY sessions to a single server over one tcp connection. Neat!

Now you can spawn as many terminal sessions as you'd like:

ssh d.term
ssh d.irc
ssh d.pico
ssh d.dotfiles

Because the attach command is essentially an "upsert", this will create or attach to each session.

Now you can use the autossh tool to make your ssh connections auto-reconnect. For example, if you have a laptop and close/open your lid it will automatically reconnect all your ssh connections:

autossh -M 0 -q d.term

Or create an alias/abbr:

abbr -a ash "autossh -M 0 -q"

ash d.term
ash d.irc
ash d.pico
ash d.dotifles

Wow! Now you can setup all your os tiling windows how you like them for your project and have as many windows as you'd like, almost replicating exactly what tmux does but with native windows, tabs, splits, and scrollback! It also has the added benefit of supporting all the terminal features your emulator supports, no longer restricted by what tmux supports.

The end-game here would be to leverage your window manager's ability to automatically arrange your windows for each project with a single command.

socket file location

Each session gets its own unix socket file. The default location depends on your environment variables (checked in priority order):

1. ZMX_DIR => uses exact path (e.g., /custom/path)
2. XDG_RUNTIME_DIR => uses {XDG_RUNTIME_DIR}/zmx (recommended on Linux, typically results in /run/user/{uid}/zmx)
3. TMPDIR => uses {TMPDIR}/zmx-{uid} (appends uid for multi-user safety)
4. /tmp => uses /tmp/zmx-{uid} (default fallback, appends uid for multi-user safety)

permissions

You can configure the permissions for the socket directory and log files using the following environment variables:

• ZMX_DIR_MODE => sets the mode for the socket and log directories (octal, defaults to 0750)
• ZMX_LOG_MODE => sets the mode for the log files (octal, defaults to 0640)

This is particularly useful when running zmx as a system service with a shared group. For example, setting ZMX_DIR_MODE=0770 and ZMX_LOG_MODE=0660 allows group members to attach to the session.

debugging

We store global logs for cli commands in {log_dir}/zmx.log. We store session-specific logs in {log_dir}/{session_name}.log. Right now they are enabled by default and cannot be disabled. The idea here is to help with initial development until we reach a stable state.

The log directory is resolved in this order:

1. ZMX_DIR/logs if ZMX_DIR is set
2. XDG_STATE_HOME/zmx/logs if XDG_STATE_HOME is set
3. HOME/.local/state/zmx/logs
4. TMPDIR/zmx-$UID (or /tmp/zmx-$UID) as a last resort

a smol contract

• Write programs that solve a well defined problem.
• Write programs that behave the way most users expect them to behave.
• Write programs that a single person can maintain.
• Write programs that compose with other smol tools.
• Write programs that can be finished.

known issues

• When upgrading versions of zmx where we make changes to the underlying IPC communication, it will kill all your sessions because it cannot communicate through the daemon socket properly
• Terminal state restoration with nested zmx sessions through SSH: host A zmx -> SSH -> host B zmx
  • Specifically cursor position gets corrupted
  • Essentially this is unspecified and unsupported behavior
• When re-attaching and kitty keyboard mode was previously enable, we try to re-send that CSI query to re-enable it
  • Some programs don't know how to handle that CSI query (e.g. psql) so when you type it echos kitty escape sequences erroneously

impl

• The daemon and client processes communicate via a unix socket
• Both daemon and client loops leverage poll(2)
• Each session creates its own unix socket file
• We restore terminal state and output using libghostty-vt

libghostty-vt

We use libghostty-vt to restore the previous state of the terminal when a client re-attaches to a session.

How it works:

• user creates session zmx attach term
• user interacts with terminal stdin
• stdin gets sent to pty via daemon
• daemon sends pty output to client and ghostty-vt
• ghostty-vt holds terminal state and scrollback
• user disconnects
• user re-attaches to session
• ghostty-vt sends terminal snapshot to client stdout

In this way, ghostty-vt doesn't sit in the middle of an active terminal session, it simply receives all the same data the client receives so it can re-hydrate clients that connect to the session. This enables users to pick up where they left off as if they didn't disconnect from the terminal session at all. It also has the added benefit of being very fast, the only thing sitting in-between you and your PTY is a unix socket.

prior art

Below is a list of projects that inspired me to build this project. Architecturally, zmx uses aspects of both projects. For example, shpool inspired the idea of having libghostty restore the terminal state on reattach. Abduco inspired the idea of one daemon (and unix socket) per session.

shpool

https://github.com/shell-pool/shpool

shpool is a service that enables session persistence by allowing the creation of named shell sessions owned by shpool so that the session is not lost if the connection drops.

abduco

https://github.com/martanne/abduco

abduco provides session management (i.e. it allows programs to be run independently from its controlling terminal). Together with dvtm it provides a simpler alternative to tmux or screen.

comparison

community tools

• emacs-term-sessions Persistent terminal sessions in Emacs, both local and remote.
• pi-zmx -- pi extension for zmx.
• zsm -- TUI session manager for zmx. List, preview, filter, and kill sessions from an interactive terminal UI.
• zmosh -- A fork of zmx that adds encrypted UDP auto-reconnect for remote sessions (like mosh).
• zmx-picker -- fzf-based session picker and project launcher. Jump to a running zmx session or start one inside any of your git/jj repos.
• rootshell -- Metal-accelerated terminal for iPhone, iPad, Vision Pro, and Mac. Lists active zmx sessions with live previews and can auto-attach on connect.