Top (Unix)

In most Unix-like operating systems, the top command produces a frequently-updated list of processes. By default, the processes are ordered by percentage of CPU usage, with only the "top" CPU consumers shown. The top command shows how much processing power and memory are being used, as well as other information about the running processes. Some versions of top allow extensive customization of the display, such as choice of columns or sorting method.

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

It is also possible to redirect the output of top in a text file.

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

History

The top command was inspired by the monitor process/topcpu command found in the VMS operating system. William LeFebvre wrote the first implementation of top in April 1984 for BSD 4.1 while a graduate student at Rice University. It was released as an Open source project under the BSD license, which allowed it to be included in numerous proprietary BSD and UNIX operating systems.

The top command has been reimplemented several times for different operating systems and under different licenses. In AIX an advanced top version was introduced in AIX 4.3 in 1999 called topas.

The first top for Linux was written by Roger Binns; the most recent and common Linux version is a full-color windowed implementation by James C. Warner that ships with the procps package.

ee also

*htop and atop commands
*pstat command
*ps command
*tkps
*gps
*vmstat command
*List of Unix programs
*Load (computing)

External links

*Linux top [http://procps.sf.net/ home page (procps)] and [http://www.linuxmanpages.com/man1/top.1.php man page]
*BSD top [http://www.unixtop.org/ home page] and [http://www.unixtop.org/top1.html man page]
*Alternate top programs for Linux include [http://www.atcomputing.nl/Tools/atop atop] (uses process accounting) and Htop