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MicroBSD like his father and mother (FreeBSD and OpenBSD) is a multi-tasking operating system. This means that it seems as though more than one program is running at once. Each program running at any one time is called a process. Every command you run will start at least one new process, and there are a number of system processes that run all the time, keeping the system functional.
Each process is uniquely identified by a number called a process ID, or PID, and, like files, each process also has one owner and group. The owner and group information is used to determine what files and devices the process can open, using the file permissions discussed earlier. Most processes also have a parent process. The parent process is the process that started them. For example, if you are typing commands to the shell then the shell is a process, and any commands you run are also processes. Each process you run in this way will have your shell as its parent process. The exception to this is a special process called init. init is always the first process, so its PID is always 1. init is started automatically by the kernel when MicroBSD starts.
Two commands are particularly useful to see the processes on the system, ps and top. The ps command is used to show a static list of the currently running processes, and can show their PID, how much memory they are using, the command line they were started with, and so on. The top command displays all the running processes, and updates the display every few seconds, so that you can interactively see what your computer is doing.
By default, ps only shows you the commands that are running and are owned by you. For example:
# ps -auwx
USER PID %CPU %MEM VSZ RSS TT STAT STARTED TIME COMMAND
root 13604 0.0 0.0 260 144 p0 R+ 2:58AM 0:00.00 (ps)
root 27595 0.0 0.0 104 376 ?? Ss 2:11PM 0:00.41 (syslogd)
root 27276 0.0 0.0 356 864 ?? Is 2:11PM 0:01.41 (sshd)
root 9046 0.0 0.0 228 460 ?? Ss 2:11PM 0:00.25 (cron)
root 7042 0.0 0.0 48 404 C0 Is+ 2:11PM 0:00.01 (getty)
root 19730 0.0 0.0 48 404 C1 Is+ 2:11PM 0:00.01 (getty)
root 12624 0.0 0.0 48 404 C2 Is+ 2:11PM 0:00.01 (getty)
root 16538 0.0 0.0 48 404 C3 Is+ 2:11PM 0:00.01 (getty)
root 13760 0.0 0.0 48 404 C5 Is+ 2:11PM 0:00.01 (getty)
root 31398 0.0 0.0 412 1264 ?? Ss 12:33AM 0:00.60 (sshd)
root 3570 0.0 0.0 1036 1524 p0 Ss 12:33AM 0:00.28 (tcsh)
root 22496 0.0 0.0 1856 688 ?? Is 12:35AM 0:00.02 (smbd)
root 26456 0.0 0.0 992 752 ?? Ss 12:36AM 0:00.51 (nmbd)
root 1 0.0 0.0 340 192 ?? Is 2:11PM 0:00.02 (init)
Display information about other users' processes as well as your own.
Display information associated with the following keywords: user, pid, %cpu, %mem, vsz, rss, tt, state, start, time, and command.
Use 132 columns to display information, instead of the default, which is your window size. If the -w option is specified more than once, ps will use as many columns as necessary without regard for your window size.
Display information about processes without controlling terminals.
As you can see in this example, the output from ps is organized into a number of columns. USER is the user that own this process, PID is the process ID. PIDs are assigned starting from 1, go up to 99999, and wrap around back to the beginning when you run out. %CPU shows the usage of the processor, %MEM shows the memory used to run this process, VSZ shows virtual size in Kbytes (alias vsize), RSS shows real memory (resident set) size of the process (in 1024 byte units), TT shows the tty the program is running on, and can safely be ignored for the moment. STAT shows the program's state, and again, can be safely ignored. STARTED shows at what time process start, TIME is the amount of time the program has been running on the CPU--this is not necessarily the elapsed time since you started the program, as some programs spend a lot of time waiting for things to happen before they need to spend time on the CPU. Finally, COMMAND is the command line that was used to run the program.
The output from top is similar. A sample session looks like this:
# top
load averages: 0.10, 0.08, 0.08 03:28:54
14 processes: 1 running, 14 idle
CPU states: 0.0% user, 0.0% nice, 0.2% system, 0.0% interrupt, 99.8% idle
Memory: Real: 7284K/16M act/tot Free: 41M Swap: 0M/140M used/tot
PID USERNAME PRI NICE SIZE RES STATE WAIT TIME CPU COMMAND
27276 root 2 0 356K 864K idle select 0:01 0.00% sshd
31398 root 2 0 456K 1288K sleep select 0:00 0.00% sshd
26456 root 2 0 992K 752K sleep select 0:00 0.00% nmbd
27595 root 2 0 104K 376K sleep select 0:00 0.00% syslogd
3570 root 18 0 1036K 1524K sleep pause 0:00 0.00% tcsh
9046 root 2 0 228K 460K idle select 0:00 0.00% cron
1 root 10 0 340K 192K idle wait 0:00 0.00% init
22496 root 2 0 1856K 688K idle select 0:00 0.00% smbd
7042 root 3 0 48K 404K idle ttyin 0:00 0.00% getty
16538 root 3 0 48K 404K idle ttyin 0:00 0.00% getty
19730 root 3 0 48K 404K idle ttyin 0:00 0.00% getty
13760 root 3 0 48K 404K idle ttyin 0:00 0.00% getty
12624 root 3 0 48K 404K idle ttyin 0:00 0.00% getty
17609 root 29 0 136K 648K run - 0:00 0.00% top
The output is split into two sections. The header (the first five lines) shows the system load averages (which are a measure of how busy the system is), The other figures in the header relate to how many processes are running (14 in this case), how much time the system is spending in different CPU states, and how much memory and swap space has been taken up.
Below that are a series of columns containing similar information to the output from ps. As before you can see the PID, the username, the amount of CPU time taken, and the command that was run. top also defaults to showing you the amount of memory space taken by the process. This is split into two columns, one for total size, and one for resident size--total size is how much memory the application has needed, and the resident size is how much it is actually using at the moment.
top automatically updates this display every two seconds; this can be changed with the -s option.
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