A process is a running program with an identity, environment, open resources, and an exit status. A server that appears unavailable may not be running, may listen on a different port, or may lack permission to access a resource. Inspect evidence before changing configuration.
Filesystem permissions control which identities can read, write, or execute a path. Grant only the access required. Environment variables configure a process and are inherited at startup; changing a shell variable does not rewrite the environment of an already-running service.
Logs and exit statuses are basic diagnostic tools. Do not solve permission errors by making everything writable or running every process with elevated privileges.
Exercise: run a local script with a configuration variable, then start a second process with a different value. Create a read-only fixture and observe a controlled write failure.
Check: you distinguish process configuration from source code and can explain the identity and path involved in a permission failure.