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Top Forums UNIX for Dummies Questions & Answers Interpretting the result of TOP command Post 7249 by Perderabo on Friday 21st of September 2001 03:58:30 PM
Old 09-21-2001
If you and I are on the system and we both run vi to edit different files, no modern kernel will give us two complete seperate copies of vi. The program's memory will be broken into segments. The text segment contains (roughly) the code and the unchanging constants. We will share one text segment bewteen us. We each get a data segment and we each get a stack. top will report the total of all the segments for each process, but you can't add them up and expect that system needs to use that much physical memory. With shared libraries, it get a bit more confused. If you use emacs and I use vi, will we have different text segments, but we both might be using the same copy of printf and other library functions. Oracle is probably using shared memory which further complicates things. Shared memory is another memory segment, and again many processes can map that seqment into their memory space. So 100 copies of a 700 MB program might easily fit in a couple of GB of memory.

In view of all this, it really isn't possible anymore to truly say how much memory a single process is using in the sense that you want. Each process really is using 700MB, but they are sharing very large chucks of this with other processes.

Most versions of top have a line that shows system-wide memory usage.
 

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top(1)							      General Commands Manual							    top(1)

NAME
top - display and update information about the top processes on the system SYNOPSIS
time] count] number] filename] pset_id] DESCRIPTION
displays the top processes on the system and periodically updates the information. Raw CPU percentage is used to rank the processes. Options recognizes the following command-line options: Set the delay between screen updates to time seconds. The default delay between updates is 5 seconds. Show only count displays, then exit. A display is considered to be one update of the screen. This option is used to select the number of displays to be shown before the program exits. This option runs the program at the same priority as if it is executed via a command so that it will execute faster (see nice(1)). This can be very useful in discovering any system problem when the system is very sluggish. This option is accessible only to users who have appropriate privileges. User ID (uid) numbers are displayed instead of usernames. This improves execution speed by eliminating the additional time required to map uid numbers to user names. Hides the individual CPU state information for systems having multiple processors. Only the average CPU status will be displayed. Show only number processes per screen. Note that, if number is greater than the maximum number of processes that can be displayed per screen, this option is ignored. But when used with option, there is no limit on the maximum number of processes that can be displayed. Output is appended to filename. When is used, defaults to 1 for and 16 for Show load averages and process state break down for system and processor set pset_id. Show only the processes running on the processor set pset_id. This option is supported only if the kernel supports processor sets functionality. Adds column PSET before column CPU for individual CPU information. Adds columns PSET before column CPU for each process informa- tion. This option is supported only if the kernel supports processor sets functionality. Show individual CPU information. By default, does not display any individual CPU information. The user can toggle between individual process information and individual CPU information by using the screen-control key. When used with the option, the option overrides the option. Screen-Control Commands When displaying multiple-screen data, recognizes the following keyboard screen-control commands: Display next screen if the current screen is not the last screen. Display previous screen if the current screen is not the first screen. Display the first (top) screen. Display individual CPU information in place of individual process information and vice versa. Program Termination To exit the program and resume normal user activities, type at any time. Display Description Three general classes of information are displayed by The first few lines at the top of the display show general information about the state of the system, including: o System name and current time. o Load averages in the last one, five, and fifteen minutes of all the active processors in the system. o Number of existing processes and the number of processes in each state (sleeping, waiting, running, starting, zombie, and stopped). o Percentage of time spent in each of the processor states (user, nice, system, idle, interrupt and swapper) per active processor on the system. o Average value for each of the active processor states (only on multi-processor systems). Reports virtual and real memory used by user processes (with the amount of memory considered "active" in parentheses) and the amount of free memory. Information about individual processes on the system. When process data cannot fit on a single screen, divides the data into two or more screens. To view multiple-screen data, use the and commands described previously. Note that the system- and memory-data displays are present in each screen of multiple- screen process data. Process data is displayed in a format similar to that used by Processor number on which the process is executing (only on multi-processor systems). Terminal interface used by the process. Process ID number. ID of the processor set to which the processor belongs. This is shown only when option is used. Name of the owner of the process. When the option is specified, the user ID (uid) is displayed instead of Current priority of the process. Nice value ranging from -20 to +20. Total virtual size of the process in kilobytes. This includes virtual sizes of text, data, stack, mmap regions, shared memory regions and IO mapped regions. This may also include virtual memory regions shared with other processes. Resident size of the process in kilobytes. It includes the sizes of all private regions in the process. The resident size information is, at best, an approximate value. Current state of the process. The various states are or Number of system and CPU seconds the process has consumed. Weighted CPU (central processing unit) percentage. Raw CPU percentage. This field is used to sort the top processes. Name of the command the process is currently running. EXAMPLES
can be executed with or without command-line options. To display five screens of data at two-second intervals then automatically exit, use: To display information about pset 2, use: To display individual CPU information in place of individual process information, use: and press the key. AUTHOR
was developed by HP and William LeFebvre of Rice University. top(1)
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