How to sort ps output

The ps command is key to understanding what’s running on your Linux system and the resources that each process is using. It’s useful to know how to display the information that ps provides in whatever way helps you focus on the problem you’re trying to resolve. One aspect of this is being able to sort the output of the ps aux command by any column to highlight particular information, such as how much memory processes are using or how long they’ve been running.

The trick involves using the ps command’s –sort option and knowing how to specify the column that you want to use for the sort. By default, ps sorts by process IDs (PIDs), showing the smallest first. PID 1 will appear at the top of the list, right under the column headings. The rest will follow in numeric order.

Here’s an example of the standard ps aux output. It probably looks familiar.

$ ps aux | head -5
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root           1  0.0  0.2 169820 14028 ?        Ss   Nov01   0:52 /lib/systemd/systemd --system --deserialize 22
root           2  0.0  0.0      0     0 ?        S    Nov01   0:00 [kthreadd]
root           3  0.0  0.0      0     0 ?        I<   Nov01   0:00 [rcu_gp]
root           4  0.0  0.0      0     0 ?        I<   Nov01   0:00 [rcu_par_gp]

Using the –sort option, you will get the same output if you sort by PID. Notice that you need to enter “pid” in lower case. However, you can change “pid” to any other column and sort by that one instead.

$ ps aux --sort pid | head -5
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root           1  0.0  0.2 169820 14028 ?        Ss   Nov01   0:52 /lib/systemd/systemd --system --deserialize 22
root           2  0.0  0.0      0     0 ?        S    Nov01   0:00 [kthreadd]
root           3  0.0  0.0      0     0 ?        I<   Nov01   0:00 [rcu_gp]
root           4  0.0  0.0      0     0 ?        I<   Nov01   0:00 [rcu_par_gp]

To see the largest values for the selected column listed first, you would have to change the sort option (e.g., -pid in place of pid). Notice how the display in this case will then start with the highest process ID. Think of – as meaning descending values (largest first) and just the name (e.g., pid) or the name with a plus sign prepended (e.g., +pid) as meaning ascending. The command shown below sorts by process ID showing the largest first.

$ ps aux --sort -pid | head -5
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
shs       316468  0.0  0.0   8092   588 pts/0    S+   14:15   0:00 head -5
shs       316467  0.0  0.0  12052  4080 pts/0    R+   14:15   0:00 ps aux --sort -pid
root      316463  0.0  0.0      0     0 ?        I    14:14   0:00 [kworker/u8:1-events_power_efficient]
root      316453  0.0  0.0      0     0 ?        I    14:09   0:00 [kworker/0:0-events]

To sort by some other column, you need to use its column name. In this example “pmem” means the percentage of memory usage and using “-pmem” means we’ll see the processes using the most memory first. You could also use “%mem” and “-%mem”.