Chapter 33: Bash uptime

What does uptime actually do? (super simple first)

uptime is one of the quickest and most useful commands in Linux. It shows you three very important pieces of information in one short line:

1. Current time on your system
2. How long the system has been running (since last boot/restart)
3. Load average for the last 1 minute, 5 minutes, and 15 minutes

That’s it – one command, one line, but it tells you a lot about system health and stability.

1. Just run it (try right now!)

Example output you might see on your laptop right now:

Or on a freshly restarted system:

Or on a server that never restarts:

2. Break down every part of the output (very important!)

Let’s take this example:

3. The MOST important part → Load Average (understand this deeply!)

Load average = average number of processes that were either running or waiting for CPU during that time period.

Rules of thumb (very useful for laptops & servers):

Examples:

• 0.65 0.48 0.42 → very relaxed, almost idle (good!)
• 1.12 0.95 0.78 → a bit busy right now, but calming down (normal when opening apps)
• 12.4 8.9 6.7 → overloaded right now, was worse 5 min ago (system feels laggy)
• 0.05 0.03 0.02 → super idle (server doing almost nothing)

Quick rule: If 1-minute load > number of cores for a long time → system is struggling.

4. Other useful ways to run uptime

5. Real-life examples you will use daily

• Laptop feels slow after many tabs & VS Code?
  Bash

  PHP

  0 1 2 3 4 5 6 7

  uptime # If load > 6–8 → check top/htop for CPU hogs

• Server running 24/7 – how stable is it?
  Bash

  PHP

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  uptime -p # up 456 days → wow, very stable!

• Before running heavy task (video render, ML training)
  Bash

  PHP

  0 1 2 3 4 5 6 7

  uptime # If load already > 4 → wait or close apps first

• Quick health check when logging into remote server
  Bash

  PHP

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  uptime && who # See uptime + who is logged in

• Watch load live
  Bash

  PHP

  0 1 2 3 4 5 6

  watch -n 2 uptime

6. Quick cheat-sheet table

7. Pro tips from daily use

• Load average is not % – it’s number of waiting/running processes → on 4-core machine, load 4.0 = fully busy but ok → load 8.0 = twice as much work as CPU can handle
• If 1-min load is high but 15-min is low → recent spike (normal when starting big app)
• If 15-min load is high → long-term overload (need to investigate)
• Very high uptime (years) is common on servers – means no crashes/reboots

Now open your terminal and try these 3 right now:

• How long has your system been running? (e.g. “up 2 days, 7 hours”)
• What’s your current load average? (e.g. 0.85 0.62 0.48)

Or ask:

• “What if my load average is always above 10?”
• “uptime vs w vs who – differences?”
• “How to check uptime on Android phone or Windows?”

We’ll go deeper together! 😄