Classic Shell Scripting

Process Listing

The most important command for listing processes is the process status command, ps. For historical reasons, there are two main flavors of ps: a System V style and a BSD style. Many systems provide both, although sometimes one of them is part of an optional package. On our Sun Solaris systems, we have:

$ /bin/ps                                
            System V-style process status
   PID TTY      TIME CMD
  2659 pts/60   0:00 ps
  5026 pts/60   0:02 ksh
 12369 pts/92   0:02 bash

$ /usr/ucb/ps                            
            BSD-style process status
   PID TT       S  TIME COMMAND
  2660 pts/60   O  0:00 /usr/ucb/ps
  5026 pts/60   S  0:01 /bin/ksh
 12369 pts/92   S  0:02 /usr/local/bin/bash

Without command-line options, their output is quite similar, with the BSD style supplying a few more details. Output is limited to just those processes with the same user ID and same controlling terminal as those of the invoker.

Like the file-listing command, ls, the ps command has many options, and both have considerable variation across Unix platforms. With ls, the -l option requesting the long output form is used frequently. To get verbose ps output, we need quite different sets of options. In the System V style, we use:

$ ps -efl                                
            System V style
 F S  UID PID PPID C PRI NI ADDR  SZ WCHAN STIME TTY   TIME CMD
19 T root   0    0 0   0 SY    ?   0       Dec 27 ?    0:00 sched
 8 S root   1    0 0  41 20    ? 106     ? Dec 27 ?    9:53 /etc/init -
19 S root   2    0 0   0 SY    ?   0     ? Dec 27 ?    0:18 pageout
19 S root   3    0 0   0 SY    ?   0     ? Dec 27 ? 2852:26 fsflush
...

whereas in the BSD style, we use:

$ ps aux                                 
            BSD style USER PID %CPU %MEM SZ RSS TT S START ...