Use a login shell for coder ssh #18805

evilhamsterman · 2025-07-08T16:52:36Z

evilhamsterman
Jul 8, 2025

Write now it looks like the coder agent handles a lot of the environment setup when connecting ssh. However this creates limitations, especially when connecting to full system environments like VMs. It does not initialize things like .profile, and on systems with systemd things like DBUS are not initialized preventing usage of things like systemd user services or environment configuration through systemd

Shell to a VM with regular SSH or Tailscale

❯ systemctl --user list-units -t service
  UNIT              LOAD   ACTIVE SUB     DESCRIPTION
  dbus.service      loaded active running D-Bus User Message Bus
❯ env|grep DBUS
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus

Shell to same VM through coder

❯ systemctl --user list-units -t service
Failed to connect to bus: No medium found
❯ env|grep DBUS
❯ echo $?
1

Rather than start the shell directly you should use the login or su commands, these are available even in most containers, and only fall back to directly starting the shell if necessary.

❯ docker run --rm -it ubuntu:noble
Unable to find image 'ubuntu:noble' locally
noble: Pulling from library/ubuntu
b08e2ff4391e: Pull complete
Digest: sha256:440dcf6a5640b2ae5c77724e68787a906afb8ddee98bf86db94eea8528c2c076
Status: Downloaded newer image for ubuntu:noble
root@8fbce12dd944:/# type login
login is /usr/bin/login
root@8fbce12dd944:/# type su
su is /usr/bin/su
root@8fbce12dd944:/# exit
exit

❯ docker run --rm -it alpine sh
Unable to find image 'alpine:latest' locally
latest: Pulling from library/alpine
Digest: sha256:8a1f59ffb675680d47db6337b49d22281a139e9d709335b492be023728e11715
Status: Downloaded newer image for alpine:latest
/ # type login
login is /bin/login
/ # type su
su is /bin/su

This is the same thing that occurs when you login from a terminal or through SSH, it takes care of changing to the $HOME directory, runs PAM to setup things like DBUS or pam_mkhomedir, etc.

deansheather · 2025-07-09T14:59:49Z

deansheather
Jul 9, 2025
Maintainer

I think the dbus thing is happening because Tailscale is started by systemd, whereas in most situations Coder is started through an init script or cloudinit.

0 replies

evilhamsterman · 2025-07-09T18:35:19Z

evilhamsterman
Jul 9, 2025
Author

No on our VMs Coder is also started by Systemd.

❯ systemctl status coder-agent.service
● coder-agent.service - Coder Agent
     Loaded: loaded (/etc/systemd/system/coder-agent.service; enabled; preset: enabled)
     Active: active (running) since Wed 2025-07-09 10:13:50 PDT; 2min 46s ago
   Main PID: 1091 (coder)
      Tasks: 134 (limit: 19095)
     Memory: 1.2G (peak: 1.3G)
        CPU: 29.923s
     CGroup: /system.slice/coder-agent.service
             ├─ 1091 ./coder agent
             ├─ 1980 filebrowser
             ├─ 2898 sh /tmp/vscode-web/bin/code-server serve-local "" "" --port 13338 --host 127.0.0.1 --accept-server-license-terms --without-connection-token --t>
             ├─ 2902 /tmp/vscode-web/node /tmp/vscode-web/out/server-main.js serve-local "" "" --port 13338 --host 127.0.0.1 --accept-server-license-terms --without>
             ├─ 6617 /bin/fish -c sh

The DBUS I'm referring to is specific to user sessions and is started by the login process.

It is typically started by pam_systemd which is only started when PAM is run which only happens on login not just when you run the shell.

You can see the difference in name of the process for Coder vs Tailscale and OpenSSH. Launching the shell as -<shell> indicates it's a login shell not just an interactive shell

Coder

❯ ps %self
    PID TTY      STAT   TIME COMMAND
 167241 pts/4    Ssl    0:00 /bin/fish

Tailscale

❯ ps %self
    PID TTY      STAT   TIME COMMAND
   5833 pts/1    Sl     0:00 -fish

OpenSSH

❯ ps %self
    PID TTY      STAT   TIME COMMAND
 160349 pts/2    Ssl    0:00 -fish

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Use a login shell for coder ssh #18805

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evilhamsterman Jul 8, 2025

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deansheather Jul 9, 2025 Maintainer

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Jul 9, 2025
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