agent-signals

056. Gemini CLI warns about limited colors on ubuntu-22.04

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Date
2026-10-30
Agents
Gemini CLI
Measured on
CI runner ubuntu-22.04 (x64), ubuntu-22.04-arm (arm64), ubuntu-24.04, ubuntu-26.04 (x64), ubuntu-24.04-arm, ubuntu-26.04-arm (arm64), macos-15, macos-26 (arm64), macos-15-intel and macos-26-intel (x64)

Measured

2026-10-30, Gemini CLI 0.66.0 (npm @google/gemini-cli), the scenario scenarios/first-run.sh gemini gemini in the scenarios workflow (run 41142220844), with a throwaway HOME, no login and no key. The scenario starts the agent in a private tmux server with tmux -f /dev/null, so tmux uses its default settings. The workflow uploaded the scrubbed screen after 20 s of each label as an artifact.

Measured on: CI runner ubuntu-22.04 (x64), ubuntu-22.04-arm (arm64), ubuntu-24.04, ubuntu-26.04 (x64), ubuntu-24.04-arm, ubuntu-26.04-arm (arm64), macos-15, macos-26 (arm64), macos-15-intel and macos-26-intel (x64).

What was measured

  1. On ubuntu-22.04 and ubuntu-22.04-arm, Gemini CLI printed four more lines above its folder-trust dialog:

    ⚠  Warning: Limited color support detected (TERM=screen). Some visual elements may not render correctly. For better
   color support in tmux, add to ~/.tmux.conf:
         set -g default-terminal "tmux-256color"
         set -ga terminal-overrides ",*256col*:Tc"

  2. On the other eight labels, Gemini CLI printed no such warning. The rest of the screen was the same on all ten labels: the dialog "Do you trust the files in this folder?" with the same three options.

  3. The warning moves the dialog down by six lines. The question, the options and the selected mark do not change.

Mechanism

The warning names TERM=screen. Gemini CLI reads the terminal type, and on the two ubuntu-22.04 images it found a type with limited colors. The tmux of an image sets TERM in the pane from its default-terminal option. The tmux version and the TERM value of the other images were not recorded, so the cause of the difference is not proved.

A reader that finds the trust dialog by its line number fails on ubuntu-22.04. A reader that finds it by its text works on all ten labels.

Incident

None.

Screens

Not measured

Screens in the corpus that name this fact