Linux

Command	Description
1	top	used to get cpu  information,memory info,process id,user who is running the process(user),what command is running.
2	df -h	used to check whether any mount point id 100% in disk space utilization.
3	du	if in the df -h command,any mount point is full. then by using du cmd delete large unwanted file.
4	dmesg	Anything that is related to hardware issue can be found here. ex: issue with memory.       issue with memory leak       issue with mother board.       issue with CPU crash.
5	iostat stands for I/o statistics	Gives read/write speed of each disk cmd: iostat 1          will refresh for every  second and display the output of iostat in the                       same putty terminal session.
6	netstat -rnv netstat | more	print network connections,routing tables,interface statistics,masquerade connections and multicast memberships.
7	free	It is used to check physical memory and virtual memory. output of free command looks like: $free                   total          used        free     shared    buff/cache    available Mem :    1016232     640252    79500   5152      296480          195024 Swap:     1048572    2724       1045848 Here: Mem - physical memory Swap - Virtual memory.
8	cat /proc/cpuinfo	To check all the CPU information of the system
9	cat /proc/meminfo	To check all the memory information of the system