Warning (2) : session_start(): open(/var/lib/php/session/sess_1ojk3jm37nghpfo2b83r9p8vmn, O_RDWR) failed: Permission denied (13) [in /var/www/develop_lwsp_jp/app/vendor/cakephp/cakephp/src/Http/Session.php, line 366]
Warning (2) : session_start(): Failed to read session data: files (path: /var/lib/php/session) [in /var/www/develop_lwsp_jp/app/vendor/cakephp/cakephp/src/Http/Session.php, line 366]
Warning (512) : Unable to emit headers. Headers sent in file=/var/www/develop_lwsp_jp/app/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php line=37 [in /var/www/develop_lwsp_jp/app/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 65]
Warning (2) : Cannot modify header information - headers already sent by (output started at /var/www/develop_lwsp_jp/app/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php:37) [in /var/www/develop_lwsp_jp/app/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 159]
Warning (2) : Cannot modify header information - headers already sent by (output started at /var/www/develop_lwsp_jp/app/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php:37) [in /var/www/develop_lwsp_jp/app/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 192]
Error: Could not start the session, headers already sent in file `CORE/src/Error/Renderer/HtmlErrorRenderer.php` on line `37`

Could not start the session, headers already sent in file `CORE/src/Error/Renderer/HtmlErrorRenderer.php` on line `37` 📋

Cake\Core\Exception\CakeException
CORE/src/Http/Session.php at line 521 (edit)
                    $this->headerSentInfo['line'],
                );
            }
            throw new CakeException($message);
        }
        if (!is_array($name)) {
            $name = [$name => $value];

If you want to customize this error message, create templates/Error/error500.php