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. shpool can be thought of as a lighter weight alternative to tmux or GNU screen. While tmux and screen take over the whole terminal and provide window splitting and tiling features, shpool only provides persistent sessions. The biggest advantage of this approach is that shpool does not break native scrollback or copy-paste.

Installation

Installing from crates.io

Run

cargo install shpool
curl -fLo "${XDG_CONFIG_HOME:-$HOME/.config}/systemd/user/shpool.service" --create-dirs https://raw.githubusercontent.com/shell-pool/shpool/master/systemd/shpool.service
sed -i "s|/usr|$HOME/.cargo|" .config/systemd/user/shpool.service
curl -fLo "${XDG_CONFIG_HOME:-$HOME/.config}/systemd/user/shpool.socket" --create-dirs https://raw.githubusercontent.com/shell-pool/shpool/master/systemd/shpool.socket
systemctl --user enable shpool
systemctl --user start shpool
loginctl enable-linger

Usage

Generally shpool is used to provide persistent sessions when sshing in to a remote host. To do so, shpool must be installed on the remote host. No extra software is required on the client. After installing and setting up, the typical usage pattern is to ssh into the host you have installed shpool on, then create a new named session by running shpool attach main. Here main is the name of the session. You'll want a separate named session for each terminal you use to connect to your remote host. If your connection drops or becomes stuck, you can ssh back into the remote host and re-attach to the same named session by running shpool attach main again.

If your terminal gets stuck and you forcibly close the window, you might find that shpool still think a terminal is connected to your session when you attempt to reattach. This is likely because an ssh proxy is holding the connection open in the vain hope that it will get some traffic again. You can just run shpool detach main to force the session to detach and allow you to attach.

Configuration

You can specify some additional configuration options to the daemon by passing a -c /path/to/config.toml flag, or by creating and editing ~/.config/shpool/config.toml. The options available are documented in detail in libshpool/src/config.rs, but there are a few common things you may wish to tweak.

Detach Keybinding

You may wish to configure your detach keybinding. By default, shpool will detach from the current user session when you press the sequence Ctrl-Space Ctrl-q (press Ctrl-Space then release it and press Ctrl-q, don't try to hold down all three keys at once), but you can configure a different binding by adding an entry like

[[keybinding]]
binding = "Ctrl-a d"
action = "Detach"

to you ~/.config/shpool/config.toml.

For the moment, control is the only modifier key supported, but the keybinding engine is designed to be able to handle more, so if you want a different one, you can file a bug with your feature request.

Session Restore Mode

Shpool can do a few different things when you re-attach to an existing session. You can choose what you want it to do with the session_restore_mode configuration option.

"screen" (default) - restore a screenful of history

The "screen" option causes shpool to re-draw sufficient output to fill the entire screen of the client terminal as well as using the SIGWINCH trick described in the "simple" section below. This will help restore context for interactive terminal sessions that are not full blown ncurses apps. "screen" is the default reattach behavior for shpool. You can choose this option explicitly by adding

session_restore_mode = "screen"

to your ~/.config/shpool/config.toml.

"simple" - only ask child processes to redraw

The "simple" option avoids restoring any output. In this reconnect mode, shpool will issue some SIGWINCH signals to try to convince full screen ncurses apps such as vim or emacs to re-draw the screen, but will otherwise do nothing. Any shell output produced when there was no client connected to the session will be lost. You can choose this connection mode by adding

session_restore_mode = "simple"

to your ~/.config/shpool/config.toml.

{ lines = n } - restore the last n lines of history

The lines option is much like the "screen" option, except that rather than just a screenful of text, it restores the last n lines of text from the terminal being re-attached to. This could be useful if you wish to have more context than a single screenful of text. Note that n cannot exceed the value of the output_spool_lines configuration option, but it defaults to the value of the lines option, so you likely won't need to change it.

session_restore_mode = { lines = n }

where n is a number to your ~/.config/shpool/config.toml.

Shell Config

bash

If you use bash, you may want to ensure that the huponexit option is set to make sure that child processes exit when you leave a shell. Without this setting, background processes you have spawned over the course of your shell session will stick around in the shpool daemon's process tree and eat up memory. To set this option add

shopt -s huponexit

to your ~/.bashrc.

Subcommands

shpool daemon

The daemon subcommand causes shpool to run in daemon mode. When running in this mode, shpool listens for incoming connections and opens up subshells, retaining ownership of them in a table. In general, this subcommand will not be invoked directly by users, but will instead be called from a systemd unit file.

shpool attach

The attach subcommand connects to the shpool daemon instance, passing in a name. If the name is new, a new shell is created, and if it already exists it just attaches to the existing session so long as no other terminal is currently connected to that session. The --ttl flag can be used to limit how long the session will last.

shpool list

Lists all the current shell sessions.

shpool detach

Detach from a one or more sessions without stopping them. Will detach the current session if run from inside a shpool session with no session name arguments.

shpool kill

Kills a named shell session.

(Optional) Automatically Connect to shpool

Explicitly named sessions

Specifying session names yourself lets you assign logical roles such as text editing to each session.

ssh config

If you typically connect to a small number of sessions with the same jobs on a particular machine, custom ssh config blocks on your client machine are probably the best fit.

To do this, you can add a config block named edit like so

Host = edit
    Hostname remote.host.example.com

    RemoteCommand shpool attach -f edit
    RequestTTY yes

to ~/.ssh/config on your client machine. You will need one such block per session name. You can then invoke this with ssh edit.

shell function

If you would rather have a little more flexibility in specifying the session name and machine you are targeting, you can make a custom shell function to let you specify both at invocation time. Add

function shpool-ssh () {
    if [ $# -ne 2 ] ; then
        echo "usage: shpool-ssh <remote-machine> <session-name>" >&2
        return 1
    fi
    ssh -t "-oRemoteCommand=shpool attach -f $2" "$1"
}

to your .bashrc then invoke it like shpool-ssh remote.host.example.com main.

Local tty based

Rather than specify an explicit name when you connect, you can set up your system to automatically generate a shpool session name based on your local terminal emulator's tty number. To do so, you can add a block of custom ssh config in the ~/.ssh/config of your local machine like

Host = by-tty
    User remoteuser
    Hostname remote.host.example.com

    RemoteCommand shpool attach -f "ssh-$(basename $(tty))"
    RequestTTY yes

which you then invoke with ssh by-tty. You can apply the same principle of using $(basename $(tty)) to get a unique id for your local terminal to the custom shell function approach as well.

The local-tty based approach has the advantage that you don't need to specify a session name, but it can run into problems if you have to close the local window and open a new terminal, which can come up if your connection freezes rather than drops.

Hacking

For information on how to develop shpool, see HACKING.md.