I have been familiar with linux since 2000, when I was at second class of university, but I have never worked on a linux machine which was hosting primary production database. The first OS I used Oracle on, was IBM AIX then, I always worked on HP/UX with a Server management team so, I never go that much deep for monitoring tools of Unix based systems, till last couple of weeks at which I started to study for managing oracle on linux exam.
Before studying, my top command usage was always like , run top / topas command then check the processes and quit the screen. I never asked myself, if I can do anything more. on top screen. Another reason about this laziness, is that , I never liked the layout of manual pages. I always got bored in 5th second . On the other hand, when you are studying something on linux, you have to leave all your boredom about man pages behind and start to read them completely.
After reading the manual, I discovered that top screen is very powerfull interactive tool on which you can do many modifications by parameters like changing the default sort option filtering by users changing the layout refresh time. You will find small tutorial about what you can do with top at the pages below.
1-Basic top screen
2- For changing the default layout press f or o in the top screen. After you press you will see the screen below. Letter with star indicator are the fields you can see on the default page.
3- When you press any of the starred letter on keyboard their star will diseppear and letter will be lowercase this means you deselected them from fields. When you press any on the non starred letter a star will apper at each one of them and letter will be uppercase This means you selected them as field.
After you change the fields top screen will be like below with UID SWAP PPID and CPU Time columns are added to fields
4- If you want to filter the processes from oracle user only (which is the best option for me) press u to filter the screen and write the username / userid . To remove the filter just press enter after u.
processes from oracle user only
5- If you want only top 10 processes from oracle user just press n and enter 10. To revert back enter 0
Ta daaa you have top 10 oracle sessions list on your top screen
6- To change the screen refreshment period press d and set the delay with seconds
After you entered the pid, It will ask you the signal with default of 15
9- Suppose that you want to change the sort order. There are two ways to do it. First way is press F and set the sorting column from the next screen by pressing the column letter . Second way is using moving by < > keys when you are at the top screen. It can also sort to a field which is not shown on the screen.
Now its all sorted bymemory usage instead of CPU
10- you can also press W and it will write your current configuration to the conf file to keep it for future usage as a default.
These are all I wanted to mention about interactive usage of TOP command as a DBA.
For more info about the top command just write man top on you command line
Wish you Happy Christmas for all.