Which of the following directories must be mounted with read and write access if it resides on its own dedicated file system?

/opt holds optional third-party application software that can remain static and be mounted read-only without impacting normal system operation.

/lib contains shared libraries and kernel modules that do not need to be written to during normal runtime and can be mounted read-only.

/etc holds system configuration files that, while occasionally modified by administrators, can be mounted read-only in certain hardened or container environments without breaking runtime operation.

/var is defined by the FHS as the directory for variable data - including logs (/var/log), spool files (/var/spool), runtime data (/var/run), and package databases - all of which are written to continuously during normal system operation. If /var resides on its own filesystem, it must be mounted read-write or the system will fail to function properly.

/usr contains user-land binaries, libraries, and documentation that are static after installation and can safely be mounted read-only.