ps aux output meaning

Question

When typing the command ps aux, what does each column of the output mean? For example:

$ ps aux  
timothy  29217  0.0  0.0 11916 4560 pts/21   S+   08:15   0:00 pine  
root     29505  0.0  0.0 38196 2728 ?        Ss   Mar07   0:00 sshd: can [priv]   
can      29529  0.0  0.0 38332 1904 ?        S    Mar07   0:00 sshd: can@notty   

Thanks and regards!

Answer 1

$ ps aux  
USER       PID  %CPU %MEM  VSZ RSS     TTY   STAT START   TIME COMMAND
timothy  29217  0.0  0.0 11916 4560 pts/21   S+   08:15   0:00 pine  
root     29505  0.0  0.0 38196 2728 ?        Ss   Mar07   0:00 sshd: can [priv]   
can      29529  0.0  0.0 38332 1904 ?        S    Mar07   0:00 sshd: can@notty  

• USER = user owning the process
• PID = process ID of the process
• %CPU = It is the CPU time used divided by the time the process has been running.
• %MEM = ratio of the process’s resident set size to the physical memory on the machine
• VSZ = virtual memory usage of entire process (in KiB)
• RSS = resident set size, the non-swapped physical memory that a task has used (in KiB)
• TTY = controlling tty (terminal)
• STAT = multi-character process state
• START = starting time or date of the process
• TIME = cumulative CPU time
• COMMAND = command with all its arguments

See the ps man page for more info.

Answer 2

This might be helpful:

Process State Codes (STAT):

• R running or runnable (on run queue)
• D uninterruptible sleep (usually IO)
• S interruptible sleep (waiting for an event to complete)
• Z defunct/zombie, terminated but not reaped by its parent
• T stopped, either by a job control signal or because it is being traced

Some extra modifiers:

• < high-priority (not nice to other users)
• N low-priority (nice to other users)
• L has pages locked into memory (for real-time and custom IO)
• s is a session leader
• l is multi-threaded (using CLONE_THREAD, like NPTL pthreads do)
• + is in the foreground process group

Answer 3

In Linux the command:

ps -aux

Means show all processes for all users. You might be wondering what the x means? The x is a specifier that means 'any of the users'. So you could type this:

ps -auroot

Which displays all the root processes, or

ps -auel

which displays all the processes from user el. The technobabble in the 'man ps' page is: "ps -aux prints all processes owned by a user named 'x' as well as printing all processes that would be selected by the -a option.