agent-signals

039. The Codex daemon outlives its TUIs and updates itself

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Date
2026-10-30
Agents
Codex CLI
Measured on
real machine

Measured

2026-10-30, Codex CLI 0.164.0 (standalone install, x86_64-unknown-linux-musl), on Linux (Debian 13, x64), in a private tmux server with a throwaway HOME and a copied login. The scenario scenarios/codex/daemon-life.sh ran two TUIs in the default daemon mode, then a --no-daemon TUI next to them, then a third daemon-mode TUI after the first ones exited. It read /proc/<pid>/fd of each process and the command line of the daemon, and logged the daemon each 10 s for 300 s after the last TUI exited. Two runs. The update of item 5 has a time only in the second run. Measured on: real machine.

What was measured

  1. Two TUIs with the same HOME used one app-server daemon, as in fact 26. The daemon held the rollout file and the lock of both sessions.
  2. A codex --no-daemon TUI that started next to the running daemon held its own rollout file and its own lock (~/.codex/thread-writer-locks/<session id>.lock). The daemon did not hold them. The daemon pid did not change.
  3. After the TUIs exited, the daemon kept running, with parent pid 1. A TUI that started 30 s later used the same daemon pid. No second daemon started. The daemon then held the lock and the rollout file of the new session too.
  4. The daemon did not exit in the 300 s after the last TUI exited, in either run.
  5. The daemon replaced itself with a newer version. In the second run, between 203 s and 213 s after the last TUI exited (about 6 minutes after the daemon started):
    • The daemon of 0.164.0 stopped.
    • ~/.codex/packages/app-server-daemon/releases/0.166.0-x86_64-unknown-linux-musl/ appeared, and a daemon from that folder started with a new pid.
    • The pid-update-loop process kept its pid, but its command line now named the 0.166.0 folder. It became the parent of the new daemon.
    • The new daemon held no rollout file and no lock of the ended sessions. In the first run, the same change happened between 0 s and 304 s after the last TUI exited. The installed codex stayed 0.164.0, and each TUI drew "Update available! 0.164.0 -> 0.166.0".

Mechanism

The daemon has its own release folder below ~/.codex/packages/, apart from the installed CLI. The pid-update-loop process updates it with no TUI. Thus the daemon can run a newer version than the TUI, and the pid of the daemon is not stable while it runs.

Incident

None recorded. A reader that keeps the daemon pid, or that reads the version of the daemon from its path, can be wrong after an update.

Screens

None.

Not measured