What is a likely reason for being unable to access a shared file system from a Linux instance?

A likely reason for being unable to access a shared file system from a Linux instance is that there are no security list rules for mount target traffic. In a Virtual Cloud Network (VCN), security lists control the inbound and outbound traffic to and from resources, such as instances within the network. If the security list associated with the subnet does not permit the necessary traffic to or from the mount target, access will be denied, resulting in the inability to connect to the shared file system.

It's essential for the appropriate rules to be defined, allowing the required protocols and ports to facilitate proper communication between the Linux instance and the mount target. Ensuring that these rules exist addresses fundamental connectivity needs for accessing shared resources. Without the appropriate security configurations, even if all other components are set up correctly, traffic will be blocked, leading to the issue described.