Sstrhsrtj

A quick and dirty method is to just pipe the output of ps aux to the sort command:

$ ps aux | sort -rn -k 5,6

Example

$ ps aux | sort -rn -k 5,6

...

root      1584  0.0  0.0  22540  1236 ?        S    07:04   0:01 hald-addon-storage: polling /dev/sr0 (every 2 sec)

root      1575  0.0  0.0  22536   872 ?        S    07:04   0:00 /usr/libexec/hald-addon-generic-backlight

root      1574  0.0  0.0  22536   880 ?        S    07:04   0:00 /usr/libexec/hald-addon-leds

root      1565  0.0  0.0  22536   876 ?        S    07:04   0:00 /usr/libexec/hald-addon-rfkill-killswitch

saml      2507  0.0  0.0  22232   500 ?        S    07:05   0:00 dbus-launch --sh-syntax --exit-with-session

root      1671  0.0  0.0  22156   936 ?        Ss   07:04   0:00 xinetd -stayalive -pidfile /var/run/xinetd.pid

...

This doesn't handle for the column headers which get mixed in with the output, but it's easy to remember on the command line, and is an acceptable way to do what you want when manually viewing this type of output.

Example

root      1791  0.0  0.0   4140   536 tty2     Ss+  07:04   0:00 /sbin/mingetty /dev/tty2

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND

root       996  0.0  0.0      0     0 ?        S    07:04   0:01 [kdmflush]

root       982  0.0  0.0      0     0 ?        S    07:04   0:00 [kvm-irqfd-clean]

More tips

An additional tip would be to pipe the entire output to another command such as less. This allows you to look at the information a page at a time and also use the arrow keys and page up/down keys to scroll back and forth through the output.

$ ps aux | sort -rn -k 5,6 | less

If your output is wrapping a lot you can also utilize the -S switch to less, which will force all the output to stay on a single line instead. You can then use your arrow keys to move left/right/up/down to see all of it.

$ ps aux | sort -rn -k 5,6 | less -S

Sorting within ps

Certain versions of ps provide the ability to use --sort. This switch can then take keys that are either prefixed with a + or a - to denote the sort order...least to greatest or greatest to least.

Examples

vsz,-rss

$ ps aux --sort=vsz,-rss | head -5

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND

root         2  0.0  0.0      0     0 ?        S    07:03   0:00 [kthreadd]

root         3  0.0  0.0      0     0 ?        S    07:03   0:00 [ksoftirqd/0]

root         4  0.0  0.0      0     0 ?        S    07:03   0:01 [migration/0]

root         5  0.0  0.0      0     0 ?        S    07:03   0:00 [watchdog/0]

+vsz,+rss

$ ps aux --sort=+vsz,+rss | head -5

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND

root         2  0.0  0.0      0     0 ?        S    07:03   0:00 [kthreadd]

root         3  0.0  0.0      0     0 ?        S    07:03   0:00 [ksoftirqd/0]

root         4  0.0  0.0      0     0 ?        S    07:03   0:01 [migration/0]

root         5  0.0  0.0      0     0 ?        S    07:03   0:00 [watchdog/0]

-vsz,-rss

$ ps aux --sort=-vsz,-rss | head -5

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND

root      1832  0.0  0.0 2088924 3312 ?        Sl   07:04   0:00 /usr/sbin/console-kit-daemon --no-daemon

saml      3517  0.2  1.2 2073196 100492 ?      Sl   07:06   0:34 /home/saml/.dropbox-dist/dropbox

saml      3516  0.0  0.8 2071032 67388 ?       Sl   07:06   0:07 /home/saml/.dropbox-dist/dropbox

saml      2657  0.1  0.7 1580936 57788 ?       Sl   07:05   0:27 nautilus

Even if ps do not reflect the actual memory used, this command is pretty helpful.

ps -eo size,pid,user,command --sort -size | awk '{ hr=$1/1024 ; printf("%13.2f Mb ",hr) } { for ( x=4 ; x<=NF ; x++ ) { printf("%s ",$x) } print "" }'

simple way is to install htop

in that you can sort process based on PID,Percentage CPU,MEM

more sophisticated

As an alternative to the BSD style arguments shown in the other answers, one can use (at least using procps, shipped by Debian and Ubuntu):

ps -eF --sort=-rss

1. Run top command


2. 
   Shift + F to sort based on field (see the full menu below)


3. Select n to sort based on memory usage

n: %MEM = Memory usage (RES)

ps aux --sort -rss is nice:

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND

user     5984  0.8  7.4 1632488 296056 ?      Sl   06:30   6:18 /usr/lib/chromium-browser/chromium-browser --type=ren

user    23934 21.7  6.0 1565600 241228 ?      Sl   15:45  40:10 /opt/atom/atom --type=renderer --enable-experimental-

user     5533  0.9  5.1 3154096 206376 ?      SLl  06:30   6:47 /usr/lib/chromium-browser/chromium-browser --enable-p

user    17306  1.7  4.9 1360648 196124 ?      Sl   18:14   0:36 /usr/lib/chromium-browser/chromium-browser --type=ren

user    22272 30.1  4.6 1347784 185032 ?      Sl   18:43   1:54 /usr/lib/chromium-browser/chromium-browser --type=ren

user    19318  0.6  3.3 1304324 133452 ?      Sl   18:27   0:09 /usr/lib/chromium-browser/chromium-browser --type=ren

user    22098  1.0  3.3 1298500 133216 ?      Sl   18:43   0:04 /usr/lib/chromium-browser/chromium-browser --type=ren

but if you want to see memory and cpu usages by application (grouped by commands):

python3.6  sum_process_resources.py 

====   CPU%   ====

0. /opt/atom/atom | 27.8

1. /usr/lib/chromium-browser/chromium-browser | 11.2

2. python3.6 | 11.0

3. /opt/google/chrome/chrome | 1.6

4. /usr/lib/xorg/Xorg | 1.4

5. /opt/Franz/franz | 0.7

====   MEM%   ====

0. /usr/lib/chromium-browser/chromium-browser | 37.2

1. /opt/google/chrome/chrome | 11.3

2. /opt/Franz/franz | 10.6

3. /opt/atom/atom | 10.1

4. /usr/lib/xorg/Xorg | 2.0

5. com.google.android.gms.persistent | 1.4

====   RSS MB   ====

0. /usr/lib/chromium-browser/chromium-browser | 1475.07 MB

1. /opt/google/chrome/chrome | 461.35 MB

2. /opt/Franz/franz | 429.04 MB

3. /opt/atom/atom | 402.18 MB

4. /usr/lib/xorg/Xorg | 78.53 MB

5. com.google.android.gms.persistent | 58.02 MB

code:

#sum_process_resources.py

from collections import OrderedDict

import subprocess



def run_cmd(cmd_string):

    """Runs commands and saves output to variable"""

    cmd_list = cmd_string.split(" ")

    popen_obj = subprocess.Popen(cmd_list, stdout=subprocess.PIPE)

    output = popen_obj.stdout.read()

    output = output.decode("utf8")

    return output



def sum_process_resources():

    """Sums top X cpu and memory usages grouped by processes"""

    ps_memory, ps_cpu, ps_rss = {}, {}, {}

    top = 6

    output = run_cmd('ps aux').split("n")

    for i, line in enumerate(output):

        cleaned_list = " ".join(line.split())

        line_list = cleaned_list.split(" ")

        if i > 0 and len(line_list) > 10:

            cpu = float(line_list[2])

            memory = float(line_list[3])

            rss = float(line_list[5])

            command = line_list[10]

            ps_cpu[command] = round(ps_cpu.get(command, 0) + cpu, 2)

            ps_memory[command] = round(ps_memory.get(command, 0) + memory, 2)

            ps_rss[command] = round(ps_rss.get(command, 0) + rss, 2)

    sorted_cpu = OrderedDict(sorted(ps_cpu.items(), key=lambda x: x[1], reverse=True))

    sorted_memory = OrderedDict(sorted(ps_memory.items(), key=lambda x: x[1], reverse=True))

    sorted_rss = OrderedDict(sorted(ps_rss.items(), key=lambda x: x[1], reverse=True))

    print("====   CPU%   ====")

    for i, k in enumerate(sorted_cpu.items()):

        if i < top:

            print("{}. {} | {}".format(i, k[0], k[1]))

    print("====   MEM%   ====")

    for i, k in enumerate(sorted_memory.items()):

        if i < top:

            print("{}. {} | {}".format(i, k[0], k[1]))

    print("====   RSS MB   ====")

    for i, k in enumerate(sorted_rss.items()):

        if i < top:

            print("{}. {} | {} MB".format(i, k[0], round((k[1]/1024), 2)))





if __name__ == '__main__':

    sum_process_resources()