tmpfs filesystem to the directory ./mem_disk as the root user inside a container, the operation fails with a "permission denied" error. root (no need for sudo). ./mem_disk directory (via mkdir -p ./mem_disk). root:root and permissions to 755 (via chown root:root ./mem_disk and chmod 755 ./mem_disk). immutable flag) with lsattr; none were found. size=100G (e.g., mount -t tmpfs tmpfs ./mem_disk), but the same error occurred. grep TMPFS /boot/config-$(uname -r) returned CONFIG_TMPFS=y, confirming tmpfs is supported. mount operations via security policies (e.g., lack of --privileged mode in Docker). Containerized root users do not have full host root privileges by default, and mount requires CAP_SYS_ADMIN capabilities, which may be blocked. tmpfs mounting. mount permissions (e.g., adjusting Docker run flags or container security settings). tmpfs mounting is restricted (e.g., using host-mounted tmpfs or alternative in-memory storage). f695a62601b9