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Linux System and Disk Commands for DevOps Engineers

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In this section, you will learn basic system, memory, disk, and navigation commands commonly used by DevOps engineers while monitoring servers and troubleshooting production issues.

free – Check Memory Usage

Used to check RAM / memory usage on a Linux server.

By default, the free command shows memory usage in kilobytes (KB).

ubuntu@manikandan:~$ free
               total        used        free      shared  buff/cache   available
Mem:          987264      334996       85924        1304      566344      472600
Swap:              0           0           0

free -h (Human Readable)

The -h option displays memory usage in MB or GB.

ubuntu@manikandan:~$ free -h
               total        used        free      shared  buff/cache   available
Mem:           964Mi       327Mi        82Mi       1.0Mi       553Mi       461Mi
Swap:             0B          0B          0B

df – Check Disk Usage

Used to check disk usage on a Linux server.

By default, df displays disk usage in kilobytes (KB).

ubuntu@manikandan:~$ df
Filesystem     1K-blocks    Used Available Use% Mounted on
tmpfs              98728    1276     97452   2% /run
/dev/sda1       47143192 7437908  39688900  16% /
tmpfs             493632       0    493632   0% /dev/shm
tmpfs               5120       0      5120   0% /run/lock
/dev/sda15        106858    6182    100677   6% /boot/efi
tmpfs              98724       4     98720   1% /run/user/1001

df -h (Human Readable)

ubuntu@manikandan:~$ df -h
Filesystem      Size  Used Avail Use% Mounted on
tmpfs            97M  1.3M   96M   2% /run
/dev/sda1        45G  7.1G   38G  16% /
tmpfs           483M     0  483M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
/dev/sda15      105M  6.1M   99M   6% /boot/efi
tmpfs            97M  4.0K   97M   1% /run/user/1001

lscpu – Check CPU Architecture

The lscpu command provides detailed information about the system's processing units. It is essential for capacity planning and understanding the hardware limits of your server.

ubuntu@manikandan:~$ lscpu | head -n 10
Architecture:            x86_64
  CPU op-mode(s):        32-bit, 64-bit
  Address sizes:         48 bits physical, 48 bits virtual
  Byte Order:            Little Endian
CPU(s):                  2
  On-line CPU(s) list:   0,1
Vendor ID:               AuthenticAMD
  Model name:            AMD EPYC 7J13 64-Core Processor

uptime – Server Load & Active Time

The uptime command quickly tells you how long the system has been running, how many users are logged in, and the system load averages for the past 1, 5, and 15 minutes.

ubuntu@manikandan:~$ uptime
 14:22:38 up 45 days,  2:11,  1 user,  load average: 0.12, 0.08, 0.05

top and htop – Interactive Process Monitoring

While ps captures a static snapshot, top provides a dynamic, real-time view of system processes, CPU utilization, and memory consumption.

(Note: Many modern servers use htop instead, offering a more visually friendly, color-coded structure).

ubuntu@manikandan:~$ top
top - 14:25:01 up 45 days,  2:13,  1 user,  load average: 0.03, 0.06, 0.04
Tasks: 104 total,   1 running, 103 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.3 us,  0.0 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st

Practice Tasks

  1. Check all system information using uname -a
  2. View how long the system has been running using uptime
  3. Check human-readable disk usage using df -h
  4. Check the size of the /etc directory using sudo du -sh /etc
  5. Check memory usage in megabytes using free -m
  6. View detailed CPU information using lscpu
  7. Indicate completion by creating a system_checked.txt file

🧠 Quick Quiz – System Basics

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Which command shows disk usage in a human-readable format?

📝 Want More Practice?

To strengthen your understanding and prepare for interviews, try the full 20-question practice quiz based on this chapter:

👉 Start System & Disk Commands Quiz (20 Questions)

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