PURBO, O. W. Ubuntu Linux Server Security Analysis and Simulation With Port Knocking & Iptable. International Journal of Basic and Applied Science, [S. l.], v. 8, n. 2, p. 36–46, 2019. Disponível em: https://www.ijobas.pelnus.ac.id/index.php/ijobas/article/view/62. Acesso em: 22 apr. 2026.