12 Essential Linux Commands to Monitor Memory Usage

1. free command

The free utility displays total, used, and free memory, along with buffers/cache and swap information. free -h Sample output:

total        used        free      shared  buff/cache   available
Mem:           7.7G        3.1G        1.1G        1.2G        3.5G        2.3G
Swap:          2.0G          0B        2.0G

2. top command

The top command provides a real‑time view of system resources, including memory, CPU, and process activity. top Sample output excerpt:

Tasks: 257 total,   1 running, 256 sleeping,   0 stopped,   0 zombie
%Cpu(s):  1.0 us,  0.7 sy,  0.0 ni, 98.3 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :   7818.7 total,   1174.9 free,   3291.9 used,   3352.0 buff/cache
MiB Swap:   2048.0 total,   2048.0 free,      0.0 used.   4183.2 avail Mem

3. vmstat command

The vmstat tool reports virtual memory statistics, including processes, CPU, and I/O. vmstat 1 5 Sample output:

procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 1  0      0 1221008 330940 922332    0    0     0     1   13   19  0  0 100  0  0

4. sar command

The sar utility collects and reports performance data for memory, CPU, and disks. sar -r Sample output:

08:10:01 PM kbmemfree kbavail kbmemused %memused kbbuffers kbcached kbcommit %commit kbactive kbinact kbdirty
08:20:01 PM   1259828  4397864   2285128   29.36   248272   3015904   2381884   15.59   2404508   2014540   52

5. /proc/meminfo file

Reading /proc/meminfo provides detailed kernel‑exposed memory metrics. cat /proc/meminfo Sample excerpt:

MemTotal:        7818180 kB
MemFree:         1207196 kB
MemAvailable:   4115164 kB
Buffers:           329540 kB
Cached:           2884056 kB
SwapCached:            0 kB

6. pmap command

The pmap command shows a process's memory map, including address ranges, permissions, and sizes. pmap PID Sample output excerpt:

0000559b7ffac000   2060K r-x-- /usr/bin/bash
0000559b801cb000    244K r--s- /usr/lib/locale/locale-archive
...

7. smem command

smem

presents memory usage in a more readable format and can sort by process. smem Sample output excerpt:

PID User   Command                     Swap   USS   PSS   RSS
    1 root   /sbin/init                    0%   0%   0.01% 0.01%
    2 root   [kthreadd]                    0%   0%   0%    0%
 2135 user   /usr/bin/firefox              0%   0.51% 1.46% 3.13%

8. atop command

atop

is an interactive system monitor offering detailed resource statistics. atop Sample output excerpt:

ATOP - myhostname          2022/01/01   08:00:01           10s elapsed
  PR  VIRT  RES  SHR S  CPU% MEM%   TIME+  COMMAND
   1  2500  456  312 S   0.0  0.0   0:00.01 bash

9. htop command

htop

provides a colorful, interactive alternative to top with easier navigation.

htop

10. glances command

glances

is a cross‑platform monitoring tool that aggregates CPU, memory, disk, network, and more, and supports plugins.

glances

11. Grafana + Prometheus

Combining Grafana with Prometheus creates a powerful open‑source stack for visualizing memory metrics and setting alerts.

12. Custom scripts

Administrators can write bespoke scripts that invoke the above commands or read files under /proc to collect, process, and display memory data tailored to specific needs.

By mastering these twelve approaches, you can obtain a complete picture of Linux memory consumption, quickly pinpoint resource bottlenecks, and keep systems running efficiently.