ps (Unix)

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In most Unix-like operating systems, the ps program (short for "process status") displays the currently-running processes. A related Unix utility named top provides a real-time view of the running processes.

In Windows PowerShell, ps is a predefined command alias for the Get-Process cmdlet, which essentially serves the same purpose.


For example:

# ps
  PID TTY          TIME CMD
 7431 pts/0    00:00:00 su
 7434 pts/0    00:00:00 bash
18585 pts/0    00:00:00 ps

Users can also utilize the ps command in conjunction with the grep command (see the pgrep and pkill commands) to find information about a single process, such as its id:

$ # Trying to find the PID of `firefox-bin` which is 2701
$ ps -A | grep firefox-bin
2701 ?        22:16:04 firefox-bin

The use of pgrep simplifies the syntax and avoids potential race conditions:

$ pgrep -l firefox-bin
2701 firefox-bin

To see every process running as root in user format:

# ps -U root -u
root     1   0.0  0.0   9436   128  -  ILs  Sun00AM     0:00.12 /sbin/init --

Break Down[edit]

Column Header Contents
 %CPU How much of the CPU the process is using
 %MEM How much memory the process is using
ADDR Memory address of the process
C or CP CPU usage and scheduling information
COMMAND* Name of the process, including arguments, if any
NI nice value
F Flags
PID Process ID number
PPID ID number of the process′s parent process
PRI Priority of the process
RSS Real memory usage
S or STAT Process status code
START or STIME Time when the process started
SZ Virtual memory usage
TIME The amount of CPU time used by the process
TT or TTY Terminal associated with the process
UID or USER Username of the process′s owner
WCHAN Memory address of the event the process is waiting for

* = Often abbreviated


ps has many options. On operating systems that support the SUS and POSIX standards, ps commonly runs with the options -ef, where "-e" selects every process and "-f" chooses the "full" output format. Another common option on these systems is -l, which specifies the "long" output format.

Most systems derived from BSD fail to accept the SUS and POSIX standard options because of historical conflicts. (For example, the "e" or "-e" option will display environment variables.) On such systems, ps commonly runs with the non-standard options aux, where "a" lists all processes on a terminal, including those of other users, "x" lists all processes without controlling terminals and "u" adds a column for the controlling user for each process. For maximum compatibility, there is no "-" in front of the "aux". "ps auxww" provides complete information about the process, including all parameters.

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