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In most Unix-like operating systems, the top command produces a constantly-updated list of all resident processes, listed in order of CPU usage. It shows how much processing power and memory are being used, as well as other information about the running processes.

It is very useful for system administrators, as it shows which users and processes are consuming the most system resources at any given time.

load averages:  0.04,  0.03,  0.03                                     16:45:14
34 processes:  33 sleeping, 1 on cpu
CPU states:     % idle,     % user,     % kernel,     % iowait,     % swap
Memory: 4096M real, 2990M free, 1396M swap in use, 2788M swap free
  PID USERNAME THR PRI NICE  SIZE   RES STATE    TIME    CPU COMMAND
  644 root       1  59    0 4544K 2904K sleep    0:00  0.37% sshd
  420 patrol     1  29   10   26M   23M sleep   16.8H  0.09% PatrolAgent
  656 gbeeker    1  49    0 2072K 1216K cpu/2    0:00  0.05% top

The top command was initially authored by William LeFebvre but has greatly benefitted from the contributions of many individuals. It was first released in April of 1984 for BSD UNIX 4.1, while the author was a graduate student at Rice University. Top was inspired by the command monitor process/topcpu found in the operating system known as VMS.

For a non-realtime list of processes, see ps.

• vmstat command
• List of Unix programs
• Load (computing)

• www.unixtop.org – Project homepage
  • Manual page
• htop – A "top" replacement for Linux: brings additional interactive features such as tree view and keyboard-controlled vertical and horizontal scrolling.