linux show current memory usage
free
#------------------------------------------------------------
#total Total installed memory
#used Memory currently in use by running processes (used= total – free – buff/cache)
#free Unused memory (free= total – used – buff/cache)
#shared Memory shared by multiple processes
#buffers Memory reserved by the OS to allocate as buffers when process need them
#cached Recently used files stored in RAM
#buff/cache Buffers + Cache
#available Estimation of how much memory is available for starting new applications, without swapping.