SSH (Secure Shell) - The Execution Layer for Agentic AI

Secure Shell (SSH) is widely used to access and administer Linux systems remotely. A successful SSH login involves more than reaching the server on TCP port 22: the client and server must establish a secure channel, the Linux host must resolve the user’s identity, the configured authentication checks must succeed, and the system must create an authorized user session.

This whitepaper explains that end-to-end workflow in a practical sequence—from DNS resolution and network connectivity through the SSH protocol handshake, sshd, PAM, NSS, SSSD and local or centralized identity sources such as LDAP, Active Directory and Kerberos. It highlights the role of /etc/nsswitch.conf in determining where Linux obtains user and group information, and shows how commands such as getent passwd can help verify identity lookup