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ps

ps

The ps command displays information about active processes. Example:

ps -au

 USER   PID  %CPU  %MEM    SZ   RSS STAT TIME COMMAND
   me  1435  12.5  21.0 15098 12058   R  2:50   doit
  you  1867   9.6   0.6   536   400   S  0:00   ls
 root   234   0.0   0.2   300   128   S  0:01   vi
 eric  5679     0     0     0     0   Z  0:12   <defunct>

Each Unix vendor seems to provide their own interpretation of the 'standard' ps command. The following is a representative example of the types of data available:

USER The user who owns the process.
PID The process identification assigned to the process when it was initiated by the system. Each process id is unique.
%CPU The percentage of CPU time used by this process. It is calculated by the formula:
(user time + system time) / (present time — start time)
%MEM The percentage of physical memory occupied by this process.
SZ The amount of non-shared memory in kilobytes allocated to the process. This includes the program's statically and dynamically allocated data area, but not the text area which is normally shared.
RSS The resident set size of the process in kilobytes. It is the amount of physical memory currently allocated to the process.
STATUS One to four letters indicating the status of the process. The first letter is the most important and indicates if the process is runnable or not runnable.
R Process is runnable
T Process is currently stopped
P Process is currently waiting for a page-in
D Process is waiting for disk I/O
S Process has been sleeping less than 20 seconds
I Process is idle (it has been sleeping for more than 20 seconds)
Z Process has terminated but not died yet. These are called
Zombies.

Zombies are usually processes waiting for their parent process. Some remain until the system reboots. They do not consume any resources other than an entry in the system table.

The second letter indicates the status of the process with respect to memory management. A W indicates the process has been swapped out.

The third letter indicates the scheduling priority. An N indicates it is running at a lower priority. A < indicates it is running at a higher priority.

The fourth letter indicates if the process has instructed the kernel of any special memory requirements.

Note

ps aux | head -11 will give the top ten processes

defunct processes are processes that are in the process of closing.

Under some Unix's there are two version of ps, the normal bin version and the compatibility version (normally in /usr/ucb/bin).  By default the ucb version takes a snaphsot of the process structure and reports on it. Depending on your Unix the standard path version will open the process structure and process it dynamically, this can lead to confusion as the process ID might tally through the report.