symfony/process · error · RuntimeException

Enabling output while the process is running is not…

Error message

Enabling output while the process is running is not possible.

What it means

enableOutput() throws this RuntimeException when the process is currently running. Like disableOutput(), toggling output capture is only allowed while the process is not started, because stream wiring is fixed at start time.

Solutions

Call enableOutput() before start()/run().
Wait for the process to finish (wait()) or stop it before enabling output.
Recreate and restart the process with output enabled.

Example fix

// before
$process->start();
$process->enableOutput(); // RuntimeException

// after
$process->enableOutput();
$process->start();

Defensive patterns

Strategy: validation

Validate before calling

if (!$process->isRunning()) {
    $process->enableOutput();
}

Try / catch

try {
    $process->enableOutput();
} catch (\RuntimeException $e) {
    // process running; wait() or stop() before toggling output
}

Prevention

Toggle output only in pre-start configuration code.
Centralize Process construction so all setters run before start() unconditionally.

When it happens

Trigger: Calling Process::enableOutput() after start()/run() on a still-running process.

Common situations: Trying to re-enable output after earlier disabling it, but doing so once the process is already running; generic configuration code that toggles output based on flags executed late in the lifecycle.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of symfony/process@99b85026db (2026-09-14). Data as JSON: /api/errors/c14644211015beb6. Report an issue: GitHub.

Appendix: source

Thrown at Process.php:612

            throw new LogicException('Output cannot be disabled while an idle timeout is set.');
        }

        $this->outputDisabled = true;

        return $this;
    }

    /**
     * Enables fetching output and error output from the underlying process.
     *
     * @return $this
     *
     * @throws RuntimeException In case the process is already running
     */
    public function enableOutput(): static
    {
        if ($this->isRunning()) {
            throw new RuntimeException('Enabling output while the process is running is not possible.');
        }

        $this->outputDisabled = false;

        return $this;
    }

    /**
     * Returns true in case the output is disabled, false otherwise.
     */
    public function isOutputDisabled(): bool
    {
        return $this->outputDisabled;
    }

    /**
     * Returns the current output of the process (STDOUT).
     *

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