Server headless detection doesn't play nicely with ssh port forwarding

[astrowonk]

Summary

The documentation says that server.headless mode is detected on linux when DISPLAY is but when I ssh in from windows either via git-bash ssh or via VS Code, the $DISPLAY variable echos empty but server.headless appears to be on (Localhost url is not displayed, and no attempt to open a browser.)

Related: headless behavior doesn't work well when developing with VS Code SSH remote. VS code will ssh Port forward and open a browser correctly if run with --server.headless false

Steps to reproduce

Run any streamlit app via ssh.

echo $DISPLAY
streamlit hello

Displayed url shows internal/external IP addresses. This implies server.headless has been set as true

streamlit hello --server.headless false

Expected behavior:

With DISPLAY not set, I expect server.headless to be false.

Actual behavior:

streamlit runs as if server.headless is true.

Is this a regression?

no

Debug info

• Streamlit version: version 1.11.0
• Python version: 3.9.12
• conda
• OS version: RHEL 7

Additional information

headless detection ostensibly exists to help with remote development but the most common way to remote develop (ssh and VS Code remote) doesn't get any benefits from it.

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[vdonato]

Hi @astrowonk,

I think the behavior is as the documentation specifies. The output of streamlit config show is "Default: false unless (1) we are on a Linux box where DISPLAY is unset, or...", which matches up with the behavior observed (although I do agree that the description could probably be reworded for clarity).

[astrowonk]

Hi @astrowonk,

I think the behavior is as the documentation specifies. The output of streamlit config show is "Default: false unless (1) we are on a Linux box where DISPLAY is unset, or...", which matches up with the behavior observed (although I do agree that the description could probably be reworded for clarity).

Ooof, ok I misread and thought it said set not unset. My apologies.

My broader point about this auto-headless behavior being unfriendly to the VS Code + ssh remote environment remains, however. I have to manually tell it to run in server.headless false to get the behavior that I think most Code users would want. (i.e. use port forwarding).

[vdonato]

My broader point about this auto-headless behavior being unfriendly to the VS Code + ssh remote environment remains, however. I have to manually tell it to run in server.headless false to get the behavior that I think most Code users would want. (i.e. use port forwarding).

Ah, okay. In that case, let me reopen this as an enhancement and change the title appropriately.

Note that I do think that this will end up quite far down in the priority list as it is still possible to have things play nicely with VS Code + ssh, it's just that having to specify the flag manually is inconvenient

[pavluka6]

This was quite helpful for me & imho should be a default behaviour