Checking system status

ps aux             <----show all process
ps auxf             <----show all process as tree format
ps a -l             <----here -l means long format, see detail

pstree             <----show process as tree format
pstree -p             <----display with pid
pstree -H 1974             <----high light the 1974 process

top
top -d 2             <----Change data with 2 second.
top -b -n 2 > /home/ray/topresult     <----run top 2 times and redirect the result to a file
in top interface:
press q is exit
press M is sort by memory
press < or > means sort by previous or next column

free -m              <----Check memory status

netstat -ntlp             <----Show the network status, here "l" means those listening process

vmstat 2             <----Check CPU status, take snapshot with 2 seconds
vmstat 2 4            <----Check CPU status, take snapshot with 2 seconds and do it 4 times
vmstat -d               <----Show disk read write status

df -h               <----Show harddisk space size

runlevel               <----Show previous and current runlevel