How do I find the process with the highest load?

You can install htop. Good thing about htop is that it will show you your usage per CPU, as well as a meaningful text graph of your memory and swap usage right at the top.

To install htop:

sudo apt-get install htop

Start it:

htop

Press F6 to sort the processes, then using the navigation key you can choose PERCENT_CPU and press enter.

Or you can use top in this way (source):

top -b -n 1 | head -n 12

^{The below is merely stolen from Unix.SE: Find the process which is taking maximum CPU usage if CPU usage is more than 60%?, though of course adapted to this question.}

list processes by specific CPU usage

ps ahux --sort=-c | awk '{if($3>0.0)printf"%s %6d %s\n",$3,$2,$11}'

This gives a list of the processes which have a CPU usage >0.0%, you can change this value according to your needs, e.g. >50.0. Each line contains the CPU usage in percent, the PID and the file of the process.

list processes with the most CPU usage

ps ahux --sort=-c | awk 'NR<=5{printf"%s %6d %s\n",$3,$2,$11}'

This shows the top 5 (NR<=5) processes currently causing the most CPU load.

Yesterday I was studying awk and I played with the other two answers. Here is the result:

• Get only the the process with the most higher CPU usage, using ps aux:

  ps auxh | awk -v max=0 '{if($3>max){CPU=$3; PID=$2; NAME=$11; max=$3}} END{printf "%5s %6d %s\n",CPU,PID,NAME}'
  

• Get the three processes with the most higher CPU usage, using top:

  top -b -n 1 | awk 'NR>7 && NR<11 {printf "top: %5s %6d %s %s\n",$9,$1,$12,$13}'
  

• Get the three processes with the most higher CPU usage, using ps aux:

  ps auxh --sort=-c | awk 'NR<=3 {printf "ps:  %5s %6d %s\n",$3,$2,$11}'
  

I've tried to run the last two commands simultaneously (with <command>; wait; <command> and <command> & <command> &), but then I've realised it is not possible at all :)

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References:

• The other two nice answers from the current question (and this comment of @αғsнιη).
• Find the max value of column 1 and print respective record from column 2 from file.
• How to run awk for some number of lines?