Which configuration management tool does not require an agent to apply changes to a Linux-based server?

Ansible does not require an agent to apply changes to a Linux-based server or other network device. It uses Secure Shell (SSH) TCP port 22 to apply the configuration. Puppet and Chef both require agents to be installed on the managed hosts. Although Cisco DNA Center is installed on top of a Linux distribution, Cisco DNA Center does not support Linux servers; it is primarily used for the management of Cisco devices. You could certainly create an extensible package to send commands to a Linux box through an SNMP agent, but currently it would need to be developed. Ansible supports Linux-based servers without an agent and without any development for communications.