You can free up unused memory under Ubuntu/Linux Mint using this command: sudo sysctl-w vm.drop_caches=3. NOTE: this action won't make your system faster nor it will affect its stability and performance, it will just clean up memory used by the Linux Kernel on caches.ere is another command that can help you free up memory either used or cached (page cache, inodes, and dentries): sudo sync && echo 3 | sudo tee /proc/sys/vm/drop_caches. NOTE: You can use cron jobs to schedule the commands above to run at specific time intervals.