Showing memory usage in Linux by process and user

There are a lot of tools for looking at memory usage on Linux systems. Some are commonly used commands like ps, while others are tools like top that allow you to display system performance stats in various ways. In this post, we’ll look at a number of commands that can be very helpful in identifying the users and processes that are using the most memory.

Using free

One of the most obvious commands for viewing memory usage is the free command, which displays total, used and free memory. With the -h option, it displays the stats in “human-readable” format, displaying the numbers in megabytes, gigabytes, etc. as appropriate.

$ free
              total       used       free      shared  buff/cache   available
Mem:        3875540    2082216     109908      141692     1683416     1413648
Swap:       3874812      35328    3839484

$ free -h
              total       used       free      shared  buff/cache   available
Mem:          3.7Gi      2.0Gi      221Mi      132Mi       1.5Gi       1.4Gi
Swap:         3.7Gi       47Mi      3.6Gi

Using top

Another of the best commands for looking at memory usage is top. One extremely easy way to see what processes are using the most memory is to start top and then press shift+m to switch the order of the processes shown to rank them by the percentage of memory each is using. Once you’ve entered shift+m, your top output should reorder the task entries to look something like what you see below. Note the %MEM column, as shown below, displays processes in memory usage order.

top - 14:22:38 up 12 min,  3 users,  load average: 0.02, 0.22, 0.32
MiB Mem :   3784.7 total,    967.8 free,   1249.0 used,   1567.9 buff/cache
MiB Swap:   3784.0 total,   3737.2 free,     46.8 used.   2170.7 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   3953 fedora    20   0 1785992 537936  76568 S   0.0  13.9   0:37.63 gnome-software
   3590 fedora    20   0 3868704 147920  96512 S   0.0   3.8   0:07.35 gnome-shell
   5885 root      20   0  664948 131048  24632 S   0.0   3.4   0:07.94 packagekitd
   5444 fedora    20   0  690380  77988  26884 S   0.0   2.0   0:02.11 python

The list will be limited by your window size, but the most significant processes with respect to memory usage will show up at the top of the process list.

If you want to focus on a single user, top can be used much in the same way that it is used above. Just add a username with the -U option as shown below and press the shift+m keys to order by memory usage:

$ top -U nemo
top - 14:28:54 up 18 min,  3 users,  load average: 0.01, 0.08, 0.22
Tasks: 242 total,   1 running, 241 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.3 us,  0.5 sy,  0.0 ni, 99.2 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :   3784.7 total,    761.7 free,   1118.5 used,   1904.5 buff/cache
MiB Swap:   3784.0 total,   3741.2 free,     42.8 used.   2298.2 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   6906 nemo      20   0  225276   3712   2944 R   1.0   0.1   0:00.10 top
   5681 nemo      20   0   30604  16004  10496 S   0.0   0.4   0:00.29 systemd
   5702 nemo      20   0  168976  22256   2048 S   0.0   0.6   0:00.00 (sd-pam)
   5718 nemo      20   0   17192   7224   5120 S   0.0   0.2   0:00.04 sshd
   5732 nemo      20   0  224656   5248   3584 S   0.0   0.1   0:00.06 bash

Using htop

The htop command will run interactively – updating its display of all running processes, along with CPU, memory, and swap usage. You can also specify options when launching htop. For example, you can add a delay between its update using the -d option.

The htop output will look like what you see below. Notice the reports on the number of running tasks, load averages, overall memory usage and swap usage that precede details on tasks using the most memory.

0[                      2.69%] Tasks: 147, 345 thr, 100 kthr; 0 running
   1[|||                    5.2%] Load average: 0.05 0.06 0.03
 Mem[||||||||||||||||1.16G/3.70G] Uptime: 81:51:21
 Swp[|||              180M/3.70G]

 PID USER PRI NI  VIRT  RES SHR S CPU% MEM% TIME+   Command
1234 user  20  0 1234M 250M 15M R 14.5 13.5 1:34.56 /usr/bin/gno
5678 user  20  0  678M 100M 10M S  6.2  0.6 0:23.12 code
4321 root  20  0  512M  80M  5M S  3.1  0.5 0:12.45 systemd
8765 user  20  0  200M  50M  3M S  1.6  0.3 0:05.67 terminal

Using vmstat

The vmstat command provides information about processes, memory, paging, block IO, traps, disks and cpu activity. Here’s an example of its output:

$ vmstat
procs -----------memory--------- ---swap-- -----io--- -system- ------cpu----
 r  b   swpd   free buff  cache   si   so    bi   bo   in   cs us sy id wa st
 0  0 185088 723712 2312 1998296   1   11   159   88  418  207  3  2 96  0  0

Note how the headings are used to separate the data into groups (e.g., memory includes swpd, fee, buff and cache). Here’s a listing of what each of these field headings means:

procs

•  r: The number of processes waiting for run time
•  b: The number of processes in uninterruptible sleep

memory

• swpd: the amount of virtual memory used
• free: the amount of idle memory
• buff: the amount of memory used as buffers
• cache: the amount of memory used as cache
• inact: the amount of inactive memory (-a option)
• active: the amount of active memory (-a option)

swap

• si: Amount of memory swapped in from disk (/s)
• so: Amount of memory swapped to disk (/s)

io

• bi: Blocks received from a block device (blocks/s)
• bo: Blocks sent to a block device (blocks/s)

system

• in: The number of interrupts per second, including the clock
• cs: The number of context switches per second

cpu (these are percentages of total CPU time)

• us: Time spent running non-kernel code (user time, including nice time)
• sy: Time spent running kernel code. (system time)
• id: Time spent idle. Prior to Linux 2.5.41, this includes IO-wait time
• wa: Time spent waiting for IO. Prior to Linux 2.5.41, included in idle
• st: Time stolen from a virtual machine. Prior to Linux 2.6.11, unknown

Using ps

The ps command includes a column that displays memory usage for each process. To get the most useful display for viewing the top memory users, you can pass the ps output to the sort command. Here’s an example that provides a very useful display. The 4^th field displays the percentage of memory used by each process.

$ ps aux | sort -rnk 4 | head -5
nemo       400  3.4  9.2 3309580 563336 ?      Sl   08:59   1:36 /usr/lib/firefox/firefox -contentproc -childID 6 -isForBrowser -prefsLen 9086 -prefMapSize 210653 -parentBuildID 20200107212822 -greomni /usr/lib/firefox/omni.ja -appomni /usr/lib/firefox/browser/omni.ja -appdir /usr/lib/firefox/browser 32469 true tab
nemo     32469  8.2  7.7 3492840 469516 ?      Sl   08:54   4:15 /usr/lib/firefox/firefox -new-window
nemo     32542  8.9  7.6 2875428 462720 ?      Sl   08:55   4:36 /usr/lib/firefox/firefox -contentproc -childID 2 -isForBrowser -prefsLen 1 -prefMapSize 210653 -parentBuildID 20200107212822 -greomni /usr/lib/firefox/omni.ja -appomni /usr/lib/firefox/browser/omni.ja -appdir /usr/lib/firefox/browser 32469 true tab
nemo       342  9.9  5.9 2854664 363528 ?      Sl   08:59   4:44 /usr/lib/firefox/firefox -contentproc -childID 5 -isForBrowser -prefsLen 8763 -prefMapSize 210653 -parentBuildID 20200107212822 -greomni /usr/lib/firefox/omni.ja -appomni /usr/lib/firefox/browser/omni.ja -appdir /usr/lib/firefox/browser 32469 true tab
nemo      2389 39.5  3.8 1774412 236116 pts/1  Sl+  09:15  12:21 vlc videos/edge_computing.mp4

In the example above (truncated for this post), sort is being used with the -r (reverse), the -n (numeric) and the -k (key) options which are telling the command to sort the output in reverse numeric order based on the fourth column (memory usage) in the output from ps. If we first display the heading for the ps output, this is a little easier to see.

$ ps aux | head -1; ps aux | sort -rnk 4 | head -5
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
nemo       400  3.4  9.2 3309580 563336 ?      Sl   08:59   1:36 /usr/lib/firefox/firefox -contentproc -childID 6 -isForBrowser -prefsLen 9086 -prefMapSize 210653 -parentBuildID 20200107212822 -greomni /usr/lib/firefox/omni.ja -appomni /usr/lib/firefox/browser/omni.ja -appdir /usr/lib/firefox/browser 32469 true tab
nemo     32469  8.2  7.7 3492840 469516 ?      Sl   08:54   4:15 /usr/lib/firefox/firefox -new-window
nemo     32542  8.9  7.6 2875428 462720 ?      Sl   08:55   4:36 /usr/lib/firefox/firefox -contentproc -childID 2 -isForBrowser -prefsLen 1 -prefMapSize 210653 -parentBuildID 20200107212822 -greomni /usr/lib/firefox/omni.ja -appomni /usr/lib/firefox/browser/omni.ja -appdir /usr/lib/firefox/browser 32469 true tab
nemo       342  9.9  5.9 2854664 363528 ?      Sl   08:59   4:44 /usr/lib/firefox/firefox -contentproc -childID 5 -isForBrowser -prefsLen 8763 -prefMapSize 210653 -parentBuildID 20200107212822 -greomni /usr/lib/firefox/omni.ja -appomni /usr/lib/firefox/browser/omni.ja -appdir /usr/lib/firefox/browser 32469 true tab
nemo      2389 39.5  3.8 1774412 236116 pts/1  Sl+  09:15  12:21 vlc videos/edge_computing.mp4

If you like this command, you can make it easier to use by setting up as an alias with a command like the one shown below. Don’t forget to add it to your ~/.bashrc file if you want to make it permanent.

$ alias mem-by-proc="ps aux | head -1; ps aux | sort -rnk 4"

You can also use a ps command to rank an individual user’s processes by memory usage. In this example, we do this by selecting a single user’s processes with a grep command:

$ ps aux | head -1; ps aux | grep ^nemo| sort -rnk 4 | more 
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
nemo     32469  7.1 11.5 3724364 701388 ?      Sl   08:54   7:21 /usr/lib/firefox/firefox -new-window
nemo       400  2.0  8.9 3308556 543232 ?      Sl   08:59   2:01 /usr/lib/firefox/firefox -contentproc -childID 6 -isForBrowser -prefsLen 9086 -prefMapSize 210653 -parentBuildID 20200107212822 -greomni /usr/lib/firefox/omni.ja -appomni/usr/lib/firefox/browser/omni.ja -appdir /usr/lib/firefox/browser 32469 true tab
nemo     32542  7.9  7.1 2903084 436196 ?      Sl   08:55   8:07 /usr/lib/firefox/firefox -contentproc -childID 2 -isForBrowser -prefsLen 1 -prefMapSize 210653 -parentBuildID 20200107212822 -greomni /usr/lib/firefox/omni.ja -appomni /usr/lib/firefox/browser/omni.ja -appdir /usr/lib/firefox/browser 32469 true tab
nemo       342 10.8  7.0 2941056 426484 ?      Rl   08:59  10:45 /usr/lib/firefox/firefox -contentproc -childID 5 -isForBrowser -prefsLen 8763 -prefMapSize 210653 -parentBuildID 20200107212822 -greomni /usr/lib/firefox/omni.ja -appomni /usr/lib/firefox/browser/omni.ja -appdir /usr/lib/firefox/browser 32469 true tab
nemo      2389 16.9  3.8 1762960 234644 pts/1  Sl+  09:15  13:57 vlc videos/edge_computing.mp4
nemo     29527  3.9  3.7 2736924 227448 ?      Ssl  08:50   4:11 /usr/bin/gnome-shell

Using ps along with other commands

Commands can get complicated when you want to compare users’ memory usages with each other. In that case, creating a by-user total and ranking them is a good technique, but it requires a little more work and requires a number of commands.

The script below counts up the memory usage for each active user (including system accounts). The first (outer) for loop creates a list of users with active processes. The second (inner) counts up the percentage of memory each of those users’ processes occupy.

#/bin/bash

echo -e USER "\t" % memory used
echo "=================="
for USER in `ps aux | grep -v USER | awk '{print $1}' | sort | uniq`
do
  sum=0
  for num in `ps aux | grep $USER | awk '{print $4}'`
  do
   sum=`echo $sum + $num | bc`
  done
  echo -e $sum "\t" $USER
done

Output from this script might look like this:

$ ./show_user_mem_usage
USER     % memory used
==================
.1       avahi
.1       chrony
.3       colord
.9       dbus
44.0     fedora
.9       geoclue
1.0      pcp
.2       polkitd
16.2     root
0        rtkit
1.5      shs
.5       systemd+

Viewing the /proc/meminfo file

The /proc/meminfofile provides a memory usage report for all kinds of system resources. The example below should give you an idea how detailed this data can be. The column command allows you to view the long list of stats in a single window. It adjusts to the width of your screen.

$ cat /proc/meminfo | column
MemTotal:        3875540 kB     SecPageTables:         0 kB
MemFree:          740468 kB     NFS_Unstable:          0 kB
MemAvailable:    2341612 kB     Bounce:                0 kB
Buffers:            2312 kB     WritebackTmp:          0 kB
Cached:          1890228 kB     CommitLimit:     5812580 kB
SwapCached:          292 kB     Committed_AS:    5574984 kB
Active:          1295012 kB     VmallocTotal:   34359738367 kB
Inactive:        1458080 kB     VmallocUsed:       51380 kB
Active(anon):     617436 kB     VmallocChunk:          0 kB
Inactive(anon):   331996 kB     Percpu:             1832 kB
Active(file):     677576 kB     HardwareCorrupted:     0 kB
Inactive(file):  1126084 kB     AnonHugePages:         0 kB
Unevictable:       20512 kB     ShmemHugePages:        0 kB
Mlocked:            5568 kB     ShmemPmdMapped:        0 kB
SwapTotal:       3874812 kB     FileHugePages:         0 kB
SwapFree:        3689724 kB     FilePmdMapped:         0 kB
Zswap:                 0 kB     CmaTotal:              0 kB
Zswapped:              0 kB     CmaFree:               0 kB
Dirty:               768 kB     Unaccepted:            0 kB
Writeback:             0 kB     HugePages_Total:       0
AnonPages:        880780 kB     HugePages_Free:        0
Mapped:           313200 kB     HugePages_Rsvd:        0
Shmem:             83768 kB     HugePages_Surp:        0
KReclaimable:      93488 kB     Hugepagesize:       2048 kB
Slab:             203160 kB     Hugetlb:               0 kB
SReclaimable:      93488 kB     DirectMap4k:      173804 kB
SUnreclaim:       109672 kB     DirectMap2M:     3893248 kB
KernelStack:        9704 kB     DirectMap1G:           0 kB
PageTables:        25668 kB 

Using dstat

The dstat command provides real-time statistics on various system resources, including CPU, memory, disk, network and more. Here’s an example of the command’s output.

$ dstat
You did not select any stats, using -cdngy by default.
----total-usage---- -dsk/total- -net/total- ---paging-- ---system--
usr sys idl wai stl| read  writ| recv  send|  in   out | int   csw
  0   0  99   0   0|   0     0 | 506B  658B|   0     0 |  91   172
  0   0  99   0   0|   0     0 |  60B  338B|   0     0 |  90   152
  3   1  96   0   0|   0     0 |  60B  354B|   0     0 | 277   518
  0   0  99   0   0|   0     0 |  60B  354B|   0     0 | 106   135
  1   0  99   0   0|   0  4096B|  60B  354B|   0     0 |  97   162
  1   0  99   0   0|   0     0 |7523B  492B|   0     0 |  81   130
  0   1  98   0   0|   0     0 | 506B  354B|   0     0 | 155   170
  0   0  99   0   0|   0     0 | 120B  424B|   0     0 |  59   102 ^C

Wrap-up

There are certainly quite a few ways to display memory usage on Linux. To focus on how much memory various processes and users are consuming, get accustomed to the command options that are available to you. And, when it’s helpful, create aliases to make your queries easier.