Chapter 31: Bash Memory Usage (free)

What does free actually do? (super simple first)

free = shows you memory usage statistics (RAM + swap) in a very quick, readable way.

It tells you:

• How much total RAM your computer has
• How much is used, free, shared, in buffers/cache, and available
• How much swap (virtual memory on disk) is used

This is one of the first commands almost every Linux user runs when the system feels slow, when a program crashes with “out of memory”, or when they want to check if they need more RAM.

1. Basic usage (try right now!)

Just type:

You will see something like this (example from a typical 16 GB laptop in 2026):

Numbers are in KiB (kibibytes = 1024 bytes) by default → hard to read.

2. The MOST important way – human readable (always use this!)

Now it shows in GB / MB – much easier:

3. Understand every column (very important – many people get confused here!)

Golden rule everyone should remember (2026 style):

• free column being low → completely normal and healthy
• Linux loves using “free” RAM for buff/cache to make disk reads super fast
• The only number you should really care about is available → if available drops below ~10–15% of total RAM for long time → system will start using swap → becomes slow

4. Very useful options (you’ll use these often)

5. Real-life examples you will use daily

• Laptop feeling slow after opening 20 Chrome tabs?
  Bash

  PHP

  0 1 2 3 4 5 6 7

  free -h # If available < 2Gi → close tabs or apps

• Checking before running heavy ML training (PyTorch / TensorFlow)
  Bash

  PHP

  0 1 2 3 4 5 6 7

  free -h # Need at least 8–10 Gi available for 16 Gi machine

• Server saying “out of memory” errors?
  Bash

  PHP

  0 1 2 3 4 5 6 7

  watch -n 3 free -h # Watch available drop → find culprit with htop / ps aux --sort=-%mem

• Is swap being used? (bad for performance)
  Bash

  PHP

  0 1 2 3 4 5 6 7

  free -h | grep Swap # If used > 100–200 MiB for long time → add more RAM or tune swappiness

• Quick check in script (example: alert if available < 2GB)
  Bash

  PHP

  0 1 2 3 4 5 6

  free -m | awk '/Mem:/ {if ($7 < 2048) print "Low memory!"; else print "OK"}'

6. Quick cheat-sheet table

7. Pro tips & common misunderstandings (very important!)

• Myth: “My free RAM is only 1 GB – bad!” → No! Low free is good if available is high – Linux is using it for cache.
• Most important number = available (It already subtracts what kernel thinks you can’t safely use)
• Swap used a lot → system will feel very slow (especially on HDD) → Solution: close heavy apps, add RAM, or lower vm.swappiness (default 60)
• Modern systems (16–32 GB) often show 0B swap used – that’s ideal

Now open your terminal and try these 3 right now:

• How much available RAM do you have right now? (e.g. 6.8Gi)
• Is your swap used 0B or some value?

Or ask:

• “What to do if available is always below 2 GB?”
• “free vs htop vs top – which shows memory best?”
• “How to reduce swap usage?”

We’ll go deeper together! 😄