Upterm

Secure Terminal Sharing

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Upterm

Upterm is an open-source solution for sharing terminal sessions instantly over the public internet via secure tunnels. Upterm is good for

  • Remote pair programming
  • Access remote computers behind NATs and firewalls
  • Remote debugging
  • <insert your creative use cases>

This is a blog post to describe Upterm in depth.

Usage

The host starts a terminal session:

$ upterm host -- bash

The host displays the ssh connection string:

$ upterm session current
=== IQKSFOICLSNNXQZTDKOJ
Command:                bash
Force Command:          n/a
Host:                   ssh://uptermd.upterm.dev:22
SSH Session:            ssh IqKsfoiclsNnxqztDKoj:MTAuMC40OS4xNjY6MjI=@uptermd.upterm.dev

The client opens a terminal and connects to the host’s session:

$ ssh IqKsfoiclsNnxqztDKoj:MTAuMC40OS4xNjY6MjI=@uptermd.upterm.dev

Installation

Mac

$ brew install owenthereal/upterm/upterm

Standalone

upterm can be easily installed as an executable. Download the latest compiled binaries and put it in your executable path.

From source

$ git clone git@github.com:owenthereal/upterm.git
$ cd upterm
$ go install ./cmd/upterm/...

Upgrade

upterm comes with a command to upgrade

Upgrade to the latest version

$ upterm upgrade

Upgrade to a specific version

$ upterm upgrade VERSION

Mac

$ brew upgrade upterm

Quick Reference

Host a terminal session that runs $SHELL with client’s input/output attaching to the host’s

$ upterm host

Display the ssh connection string and share it with the client(s)

$ upterm session current
=== SESSION_ID
Command:                /bin/bash
Force Command:          n/a
Host:                   ssh://uptermd.upterm.dev:22
SSH Session:            ssh TOKEN@uptermd.upterm.dev

A client connects to the host session with ssh

$ ssh TOKEN@uptermd.upterm.dev

Host a terminal session that only allows specified client public key(s) to connect

$ upterm host --authorized-key PATH_TO_PUBLIC_KEY

Host a terminal session that only allows specified GitHub user client public key(s) to connect. This is compatible with --authorized-keys.

$ upterm host --github-user username

Host a terminal session that only allows specified GitLab user client public key(s) to connect. This is compatible with --authorized-keys.

$ upterm host --gitlab-user username

Host a session with a custom command

$ upterm host -- docker run --rm -ti ubuntu bash

Host a session that runs ‘tmux new -t pair-programming’ and force clients to join with tmux attach -t pair-programming. This is similar to what tmate offers.

$ upterm host --force-command 'tmux attach -t pair-programming' -- tmux new -t pair-programming

Connect to uptermd.upterm.dev via WebSocket

$ upterm host --server wss://uptermd.upterm.dev -- bash

A client connects to the host session via WebSocket

$ ssh -o ProxyCommand='upterm proxy wss://TOKEN@uptermd.upterm.dev' TOKEN@uptermd.upterm.dev:443

More advanced usage is here.

Tips

Why doesn’t upterm session current show current session in Tmux?

upterm session current needs the UPTERM_ADMIN_SOCKET environment variable to function. And this env var is set in the specified command. Unfotunately, Tmux doesn’t carry over environment variables that are not in its default list to any Tmux session unless you tell it to (Ref). So to get upterm session current to work, add the following line to your ~/.tmux.conf

set-option -ga update-environment " UPTERM_ADMIN_SOCKET"

How to make it obvious that I am in an upterm session?

It can be confusing whether your shell command is running in an upterm session or not, especially if the shell command is bash or zsh. Add the following line to your ~/.bashrc or ~/.zshrc and decorate your prompt to show a sign if the shell command is in a terminal session:

export PS1="$([[ ! -z "${UPTERM_ADMIN_SOCKET}"  ]] && echo -e '\xF0\x9F\x86\x99 ')$PS1" # Add an emoji to the prompt if `UPTERM_ADMIN_SOCKET` exists

Demo

asciicast

How it works

You run the upterm program by specifying the command for your terminal session. Upterm starts an SSH server (a.k.a. sshd) in the host machine and sets up a reverse SSH tunnel to a Upterm server (a.k.a. uptermd). Clients connect to your terminal session over the public internet via uptermd using ssh using TCP or WebSocket. A community Upterm server is running at uptermd.upterm.dev and upterm points to this server by default.

upterm flowchart

A note about RSA keys

Since openssh 8.8 (2021-09-26), the host algorithm type SHA-1 (ssh-rsa) was retired in favor of SHA-2 (rsa-sha2-256 or rsa-sha2-512) (release note). Unfortunately, due to a shortcoming in Go’s x/crypto/ssh package, upterm does not completely support SSH clients using SHA-2 keys: only the old SHA-1 ones will work.

You can check your openssh version with the following:

$ ssh -V

If you are not sure what type of keys you have, you can check with the following:

$ find ~/.ssh/id_*.pub -exec ssh-keygen -l -f {} \;

Until this is sorted out, you are recommended to use key with another algorithm, e.g. Ed25519.

If you’re curious about the inner workings of this problem, have a look at:

  • https://github.com/owenthereal/upterm/issues/93#issuecomment-1045387517
  • https://github.com/golang/go/issues/49952

Deploy Uptermd

Kubernetes

You can deploy uptermd to a Kubernetes cluster. Install it with helm:

$ helm repo add upterm https://upterm.dev
$ helm repo update
$ helm search repo upterm
NAME            CHART VERSION   APP VERSION     DESCRIPTION
upterm/uptermd  0.1.0           0.4.1           Secure Terminal Sharing
$ helm install uptermd upterm/uptermd

Heroku

The cheapest way to deploy a worry-free Upterm server (a.k.a. uptermd) is to use Heroku. Heroku offers free Dyno hours which should be sufficient for most casual uses.

You can deploy with one click of the following button:

Deploy

You can also automate the deployment with Heroku Terraform. The Heroku Terraform scripts are in the terraform/heroku folder. A util script is provided for your convenience to automate everything:

$ git clone https://github.com/owenthereal/upterm
$ cd upterm

Provision uptermd in Heroku Common Runtime. Follow instructions.

$ bin/heroku-install

Provision uptermd in Heroku Private Spaces. Follow instructions.

$ TF_VAR_heroku_region=REGION TF_VAR_heroku_space=SPACE_NAME TF_VAR_heroku_team=TEAM_NAME bin/heroku-install

You must use WebScoket as the protocol for a Heroku-deployed Uptermd server because the platform only support HTTP/HTTPS routing. This is how you host a session and join a session:

Use the Heroku-deployed Uptermd server via WebSocket

$ upterm host --server wss://YOUR_HEROKU_APP_URL -- YOUR_COMMAND

A client connects to the host session via WebSocket

$ ssh -o ProxyCommand='upterm proxy wss://TOKEN@YOUR_HEROKU_APP_URL' TOKEN@YOUR_HEROKU_APP_URL:443

Digital Ocean

There is an util script that makes provisioning Digital Ocean Kubernetes and an Upterm server easier:

TF_VAR_do_token=$DO_PAT \
TF_VAR_uptermd_host=uptermd.upterm.dev \
TF_VAR_uptermd_acme_email=YOUR_EMAIL \
TF_VAR_uptermd_helm_repo=http://localhost:8080 \
TF_VAR_uptermd_host_keys_dir=PATH_TO_HOST_KEYS \
bin/do-install

Systemd

A hardened systemd service is provided in systemd/uptermd.service. You can use it to easily run a secured uptermd on your machine:

$ cp systemd/uptermd.service /etc/systemd/system/uptermd.service
$ systemctl daemon-reload
$ systemctl start uptermd

How is Upterm compared to prior arts?

Upterm is an alternative to Tmate.

Tmate is a fork of an older version of Tmux. It adds terminal sharing capability on top of Tmux 2.x. Tmate doesn’t intend to catch up with the latest Tmux, so any Tmate & Tmux users must maintain two versions of the configuration. For example, you must bind the same keys twice with a condition.

Upterm is designed from the group up not to be a fork of anything. It builds around the concept of linking the input & output of any shell command between a host and its clients. As you see above, you can share any command besides tmux. This opens up a door for securely sharing a terminal session using containers.

Upterm is written in Go. It is more friendly hackable than Tmate that is written in C because Tmux is C. The Upterm CLI and server (uptermd) are compiled into a single binary. You can quickly spawn up your pairing server in any cloud environment with zero dependencies.

License

Apache 2.0