Linux: Monitor Processes, “top” Tutorial
top is a command line program that lets you monitor CPU usage.
In terminal, type
top. Then, try the following in order:
- 【z】 → toggle color.
- 【x】 → toggle coloring of sort column.
- 【s 9 9 Enter ↵】 → set update frequency to every 99 seconds.
- 【Space】 → force a update.
- 【>】 → change the sort column to the right of current sort column.
- 【<】 → change the sort column to the left.
- 【R】 → toggel reverse sort order.
- 【O k Enter ↵】 → order by CPU usage. (also 【P】)
- 【O n Enter ↵】 → order by memory usage. (also 【M】)
- 【O a Enter ↵】 → order by pid.
- 【O x Enter ↵】 → order by process name.
- 【c】 → show full path of commands.
- 【k】 → kill a process by pid.
- 【u user】 → show only processes of a user.
- 【h】 → help.
- 【q】 → quit.
top - 12:59:21 up 20:59, 0 users, load average: 1.05, 0.93, 0.90 current system past 1 min, 5 min, 15 min time uptime
- If you have 1 CPU core, than load average of 1 means 100% CPU usage.
- If you have 2 CPU core, than load average of 2 means 100% CPU usage.
- If you have n CPU core, than load average of n means 100% CPU usage.
“load average”/“number of cpu core” = CPU load.
Higher than 1 means overloaded.
Tasks: 139 total, 1 running, 137 sleeping, 0 stopped, 1 zombie
Cpu(s): 5.4%us, 32.4%sy, 0.0%ni, 62.2%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st user system niced idle IO wait
- us = User CPU time → The time the CPU has spent running users' processes that are not niced.
- sy = System CPU time → The time the CPU has spent running the kernel and its processes.
- ni = Nice CPU time → The time the CPU has spent running users' proccess that have been niced. (see:
- wa = iowait → Amount of time the CPU has been waiting for I/O to complete.
- hi = Hardware IRQ → The amount of time the CPU has been servicing hardware interrupts.
- si = Software Interrupts → The amount of time the CPU has been servicing software interrupts.
- st = Steal Time → The amount of CPU “stolen” from this virtual machine by the hypervisor for other tasks (such as running another virtual machine).
Mem: 800340k total, 652680k used, 147660k free, 45688k buffers Swap: 818172k total, 8584k used, 809588k free, 315372k cached
Actual free memory (RAM) available to programs is: free + buffers + cached. For detail, see: Linux: Find How Much Memory is Free.
Better is to see memory usage visually. Use
〔►see Linux: Monitor Processes, “htop” Tutorial〕
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
- PID = Process Id
- USER = User Name
- PR = Priority
- NI = Nice value
- VIRT = Virtual Image (kb)
- RES = Resident size (kb)
- SHR = Shared Mem size (kb)
- S = Process Status
- %CPU = CPU usage
- %MEM = Memory usage (RES)
- COMMAND = Command name/line
- TIME+ = CPU Time, hundredths
For some explanation of these, do
Common Top Options
top -d 9run top with delay (update frequency) set to 9 seconds.
top -u johnshow only processes from user john.
top -n 10run top with 10 updates, then exit.
top -b -n 1 > top_out.txt. Dump top output as plain text to a file. The “-b” means batch mode. Basically, in batch mode, it dosn't accept any interactive inputs. If you run
top -b, use 【Ctrl+c】 to exit.
Better top: htop
unix “top” is a very old program. It has some problems. For example, sometimes you want to view one particular process, but if you don't have a long screen, it's very diffucult or impossible, unless you find the pid first than call
top -p pid.
A much better one is “htop”. See Linux: Monitor Processes, “htop” Tutorial.