composer/composer · error · RuntimeException

You are on an old Windows / old PHP combo which does not all

Error message

You are on an old Windows / old PHP combo which does not allow Composer to use junctions/symlinks and this path repository has symlink:true in its options so copying is not allowed

What it means

Thrown by PathDownloader::computeAllowedStrategies() (line 297-303) on Windows when the symlink strategy is selected but safeJunctions() returns false. safeJunctions() requires proc_open and Windows >= 7 (version 6.1) due to a PHP bug (bugs.php.net/77552) that makes junction removal data-loss-prone on older combos. If mirror is not an allowed fallback (symlink:true forced), it throws.

Source

Thrown at src/Composer/Downloader/PathDownloader.php:299

        $mirrorPathRepos = Platform::getEnv('COMPOSER_MIRROR_PATH_REPOS');
        if ((bool) $mirrorPathRepos) {
            $currentStrategy = self::STRATEGY_MIRROR;
        }

        $symlinkOption = $transportOptions['symlink'] ?? null;

        if (true === $symlinkOption) {
            $currentStrategy = self::STRATEGY_SYMLINK;
            $allowedStrategies = [self::STRATEGY_SYMLINK];
        } elseif (false === $symlinkOption) {
            $currentStrategy = self::STRATEGY_MIRROR;
            $allowedStrategies = [self::STRATEGY_MIRROR];
        }

        // Check we can use junctions safely if we are on Windows
        if (Platform::isWindows() && self::STRATEGY_SYMLINK === $currentStrategy && !$this->safeJunctions()) {
            if (!in_array(self::STRATEGY_MIRROR, $allowedStrategies, true)) {
                throw new \RuntimeException('You are on an old Windows / old PHP combo which does not allow Composer to use junctions/symlinks and this path repository has symlink:true in its options so copying is not allowed');
            }
            $currentStrategy = self::STRATEGY_MIRROR;
            $allowedStrategies = [self::STRATEGY_MIRROR];
        }

        // Check we can use symlink() otherwise
        if (!Platform::isWindows() && self::STRATEGY_SYMLINK === $currentStrategy && !function_exists('symlink')) {
            if (!in_array(self::STRATEGY_MIRROR, $allowedStrategies, true)) {
                throw new \RuntimeException('Your PHP has the symlink() function disabled which does not allow Composer to use symlinks and this path repository has symlink:true in its options so copying is not allowed');
            }
            $currentStrategy = self::STRATEGY_MIRROR;
            $allowedStrategies = [self::STRATEGY_MIRROR];
        }

        return [$currentStrategy, $allowedStrategies];
    }

    /**

View on GitHub (pinned to 6ffc117740)

Solutions

1. Upgrade PHP to 7.2.16+ or 7.3.3+ so junctions are safe
2. Upgrade to Windows 7 (6.1) or newer
3. Remove the symlink:true option so Composer can mirror instead of junction

Example fix

// before
"options":{"symlink":true}
// after (allows mirror fallback on old Windows/PHP)
"options":{"symlink":null}

// On old Windows/PHP, do not force symlink-only
$options = $package->getTransportOptions();
if (PHP_OS_FAMILY === 'Windows' && PHP_VERSION_ID < 70216 && ($options['symlink'] ?? null) === true) {
    $options['symlink'] = null; // allow mirror fallback
    $package->setTransportOptions($options);
}

When it happens

Trigger: Platform::isWindows() is true, STRATEGY_SYMLINK is current, safeJunctions() is false (Windows < 7 or PHP < 7.2.16/7.3.3), and symlink:true in transport options excludes mirroring.

Common situations: Running Composer on an old Windows Server / old PHP where junctions are unsafe, while a path repo forces symlink:true.

Related errors

• Cannot junction to "%s" as it is not a directory.
• Symlink from "%s" to "%s" failed!
• Could not reliably remove junction for package {name}
• Failed to create junction to "%s" at "%s".
• %s is not a junction and thus cannot be removed as one

AI-assisted analysis of composer/composer@6ffc117740 (2026-08-07). Data as JSON: /api/errors/0d6e688cb304e4d7. Report an issue: GitHub.