Using the ps aux Command in Linux
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ps aux command is a tool to monitor processes running on your Linux system. A process is associated with any program running on your system, and is used to manage and monitor a program’s memory usage, processor time, and I/O resources. Since the
ps aux command displays an overview of all the processes that are running, it is a great tool to understand and troubleshoot the health and state of your Linux system. This guide provides an introduction to the
ps aux command with brief examples to help you interpret its output.
ps command without any options displays information about processes that are bound by the controlling terminal.
The command returns a similar output:
PID TTY TIME CMD 285 pts/2 00:00:00 zsh 334 pts/2 00:00:00 ps
The default output of the
ps command contains four columns that provide the following information:
PID: The process ID is your system’s tracking number for the process. The
PIDis useful when you need to use a command like
nice, which take a PID as their input.
TTY: The controlling terminal associated with the process. Processes that do not originate from a controlling terminal and were initiated by the system at boot are displayed with a question mark.
TIME: The CPU usage of the process. Displays the amount of CPU time used by the process. This value is not the run time of the process.
CMD: The name of the command or executable that is running. The output only includes the name of the command or executable and does not display any options that were passed in.
ps command accepts three different styles of options; UNIX, BSD, and GNU. You can use a mix of each style, however, you may notice inconsistent behavior across Linux distributions.
When using UNIX-style options, your option(s) must be preceded by a dash (
-) and can be grouped together. For example, the
-auxoptions in the
ps -auxcommand is preceded by a dash when using the UNIX style.
When using BSD-style options with the
pscommand, you must exclude the dash (
-), however, you can group your options. For example, notice the
ps auxcommand’s options;
auxis formatted in the BSD style.
GNU-style options are preceded by two dashes (
--), and are reserved for long options. For example, the
ps --quick-pid 10946command uses the long option
--quick-pidto display running process information by a specific PID. In the example,
10946is the process PID.
View All of Your System’s Processes
By default, the
ps command displays only the processes associated with your current terminal session. However, you may want to view all the processes that the current user owns, for example if you have multiple terminal sessions running for the same user. In that case, issue the
ps x command. Also, notice that the command is using the BSD-style option.
ps x command returns an additional column called sate information (
STAT). This column can display a large number of possible values depending on the process it displays. For example, a lowercase
s indicates that the process is a session leader (i.e., the root process). A capital
S means that the process is in an interruptible sleep state, and is waiting for some event, like user input.
R means that the command is actively running.
T means that the process has stopped; like when you enter control-Z in the vi text editor. The
+ means it is a foreground process.
Take a look at the following example and notice the different states for each process displayed in the
PID TTY STAT TIME COMMAND 285 pts/2 Ss 0:00 -zsh 343 pts/2 T 0:00 vi foo 351 pts/3 Ss+ 0:00 -zsh 439 pts/2 R+ 0:00 ps -x
Viewing the Process Hierarchy
init process is the first process started by the Linux kernel when a system boots. Every other process on your system is a child of the
init process. You can view this hierarchy using the
H options. The
e option causes
ps to list all processes in the system, regardless of the owner or controlling terminal. The
H option formats the
CMD column’s data to display the parent-child relationship between processes.
PID TTY TIME CMD 1 ? 00:00:00 init 227 ? 00:00:00 init 228 ? 00:00:00 init 229 pts/0 00:00:15 docker 240 ? 00:00:00 init <defunct> 247 ? 00:00:00 init 248 pts/1 00:00:10 docker-desktop- 283 ? 00:00:00 init 284 ? 00:00:00 init 285 pts/2 00:00:00 zsh 343 pts/2 00:00:00 vi 528 pts/2 00:00:00 ps 349 ? 00:00:00 init 350 ? 00:00:00 init 351 pts/3 00:00:00 zsh
Alternatively, you can get a prettier output with a few more columns by using the
ps -axjf command.
PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND 0 1 0 0 ? -1 Sl 0 0:00 /init 1 227 227 227 ? -1 Ss 0 0:00 /init 227 228 227 227 ? -1 S 0 0:00 \_ /init 228 229 229 229 pts/0 229 Ssl+ 1000 0:15 | \_ docker 227 240 227 227 ? -1 Z 0 0:00 \_ [init] <defunct> 227 247 227 227 ? -1 S 0 0:00 \_ /init 247 248 248 248 pts/1 248 Ssl+ 0 0:10 \_ /mnt/wsl/docker-desktop/docker-desktop-proxy 1 283 283 283 ? -1 Ss 0 0:00 /init 283 284 283 283 ? -1 S 0 0:00 \_ /init 284 285 285 285 pts/2 559 Ss 1000 0:00 \_ -zsh 285 343 343 285 pts/2 559 T 1000 0:00 \_ vi foo 285 559 559 285 pts/2 559 R+ 1000 0:00 \_ ps axjf 1 349 349 349 ? -1 Ss 0 0:00 /init 349 350 349 349 ? -1 S 0 0:00 \_ /init 350 351 351 351 pts/3 351 Ss+ 1000 0:00 \_ -zsh
The additional columns provide the following information:
PPID: Displays the parent process ID. In the above example, the
vicommand has a
285, which matches the
PIDof the Z shell process running above it.
SID: This column displays the session ID. The value is usually the same as the PID of the process that started the chain.
PGID: This ID shows the parent group process ID.
TPGID: This is the terminal sessions ID with which the process is associated. If there is no terminal that is associated, then
UID: The user ID associated with the process is displayed in this column.
Now that you understand the basics of the
ps command, this section covers the benefits to the
ps aux command. The
ps aux displays the most amount of information a user usually needs to understand the current state of their system’s running processes. Take a look at the following example:
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.0 892 572 ? Sl Nov28 0:00 /init root 227 0.0 0.0 900 80 ? Ss Nov28 0:00 /init root 228 0.0 0.0 900 88 ? S Nov28 0:00 /init zaphod 229 0.0 0.1 749596 31000 pts/0 Ssl+ Nov28 0:15 docker root 240 0.0 0.0 0 0 ? Z Nov28 0:00 [init] <defunct> root 247 0.0 0.0 900 88 ? S Nov28 0:00 /init root 248 0.0 0.1 1758276 31408 pts/1 Ssl+ Nov28 0:10 /mnt/wsl/docker-desktop/docker-desktop-proxy root 283 0.0 0.0 892 80 ? Ss Dec01 0:00 /init root 284 0.0 0.0 892 80 ? R Dec01 0:00 /init zaphod 285 0.0 0.0 11964 5764 pts/2 Ss Dec01 0:00 -zsh zaphod 343 0.0 0.0 23764 9836 pts/2 T 17:44 0:00 vi foo root 349 0.0 0.0 892 80 ? Ss 17:45 0:00 /init root 350 0.0 0.0 892 80 ? S 17:45 0:00 /init zaphod 351 0.0 0.0 11964 5764 pts/3 Ss+ 17:45 0:00 -zsh zaphod 601 0.0 0.0 10612 3236 pts/2 R+ 18:24 0:00 ps aux
ps aux command displays more useful information than other similar options. For example, the
UID column is replaced with a human-readable
ps aux also displays statistics about your Linux system, like the percent of CPU and memory that the process is using. The
VSZ column displays amount of virtual memory being consumed by the process.
RSS is the actual physical wired-in memory that is being used. The
START column shows the date or time for when the process was started. This is different from the CPU time reported by the
ps command has many other available options. For example,
ps allows you to customize output columns so you can view your system’s data in a format you prefer. You can filter based on the user, process name, or terminal. You can tell
ps to print its output more verbosely and to ignore your screen width. You can spend more time learning what else
ps can accomplish by reading its man-page on your Linux system.
top as an Alternative to the
top command is also a good tool to use to monitor your system’s processes. One benefit to the
top command is that it updates its values and statistics in real time. You can also sort its output by CPU usage, and it allows you to kill a process using a semi-graphical UI. If you’d like to learn more about the
top command, check out the Using top to Monitor Server Performance guide.
You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.
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