A system administrator has just installed a new Linux distribution. The distribution is configured to be "secure out of the box". The system administrator cannot make updates to certain system files…

SELinux enforces mandatory access controls (MAC) at the kernel level, which can deny modifications to system files and services even for privileged users when operating in enforcing mode, generating AVC denial errors. A distribution advertised as 'secure out of the box' almost certainly has SELinux in enforcing mode, so reviewing and adjusting SELinux policies or file context labels is the correct first troubleshooting step.

Resetting root permissions on systemd files addresses discretionary access control (DAC) at the filesystem level but would have no effect on denials enforced by SELinux mandatory access controls, which operate independently of standard Unix permissions.

Performing actions as root bypasses DAC restrictions but does not bypass SELinux MAC enforcement - SELinux can and does deny operations initiated by the root user when policy rules prohibit them.

Firewall software manages inbound and outbound network traffic and has no bearing on local filesystem permissions or the ability to modify system files and services.