The Linux top command shows what is running.
Each of the bits of software above is known as a “process.” Big pieces of
software such as Apache and MySQL will often have a parent process with a
lot of child processes and so could appear more than once in the list. In this
benign example, a child process of the Apache Web server is currently the
greediest software, using 7.6% of the CPU and 1.6% of the memory. The
view will refresh every three seconds. Check the Mem column to see whether
anything is consistently eating up a large portion of the memory.