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Monitoring System Resources (free, uptime)

1. Introduction to Resource Monitoring​

Monitoring system resources helps to:

  • Detect performance bottlenecks.
  • Prevent system crashes caused by excessive memory or CPU usage.
  • Optimize resource allocation for better performance.
  • Troubleshoot issues like memory leaks or high CPU loads.

2. Checking Memory Usage with free​

The free command is used to display the system’s memory (RAM) and swap usage.

Syntax:​

free [options]

Key Options​

OptionsDescription
-hDisplay values in human-readable format (e.g., MB, GB).
-b, -k, -mShow output in bytes, kilobytes, or megabytes.
-tInclude total memory usage.
-s <n>Continuously update output every n seconds.

Examples​

1. Basic Memory Report​
free

Expected Output:

              total        used        free      shared  buff/cache   available
Mem:       16389804     8093228     3245384      102092     5041212     7895680
Swap:       2097152           0     2097152
  • total: Total installed RAM.
  • used: Memory currently in use by processes.
  • free: Unused memory available.
  • shared: Memory shared between processes (e.g., tmpfs).
  • buff/cache: Memory reserved for disk buffers and cache.
  • available: Estimated memory available for starting new applications without swapping.
  • swap: Disk-based virtual memory for overflow when RAM is full.
2. Human-Readable Output​
free -h

Expected Output:

              total        used        free      shared  buff/cache   available
Mem:            15G         8G        3.1G       100M         4G        7.5G
Swap:           2G          0B        2G
  • The -h option simplifies interpretation with MB and GB units.
3. Continuous Monitoring​
free -s 5
  • This updates the output every 5 seconds for continuous monitoring.

Analyzing Swap Memory​

Check swap usage to determine if the system is relying heavily on virtual memory. High swap usage may indicate low RAM availability, causing performance slowdowns.

free -h | grep Swap

Expected Output:

Swap:           2.0G       256M      1.7G
  • 256M is used, which suggests active swapping.

3. Monitoring Uptime and System Load with uptime​

The uptime command provides information about:

  • How long the system has been running.
  • Current number of logged-in users.
  • Load averages (CPU load) over 1, 5, and 15 minutes.

Syntax

uptime

Examples​

Display System Uptime​
uptime

Expected Output:

15:42:23 up 10 days, 4:12,  2 users,  load average: 0.58, 0.49, 0.40
  • 15:42:23: Current time.
  • up 10 days, 4:12: System has been running for 10 days and 4 hours.
  • 2 users: Number of logged-in users.
  • Load averages: Average CPU load over 1, 5, and 15 minutes.
2. Checking Load Averages Only​
uptime | awk '{print $8, $9, $10}'

Expected Output:

0.58, 0.49, 0.40
  • Values close to 0.00 indicate low load.
  • Values near 1.00 per core indicate full utilization.
  • Higher values may signal CPU bottlenecks or overloaded processes.

Interpreting Load Averages:​

  • Single-core CPU: Load of 1.0 means full capacity.
  • Dual-core CPU: Load of 2.0 is fully utilized.
  • Values above capacity imply queued tasks, indicating performance issues.

4. Practical Scenarios and Use Cases​

Scenario 1: Detecting High Memory Usage​

1. Check memory:​
free -h
2. Analyze processes:​
ps aux --sort=-%mem | head -5
  • Find top memory-consuming processes.

Scenario 2: Monitoring Swap Usage​

1. Check swap status:​
free -h | grep Swap
2. Disable swapping temporarily:​
sudo swapoff -
3. Re-enable swapping:​
sudo swapon -a

Scenario 3: Detecting High CPU Load​

1. Monitor load averages:​
uptime
2. Check CPU usage with top or htop:​
top
3. Restart high-load services:​
sudo systemctl restart apache2

5. Combining Tools for Better Insights​

1. Memory Monitoring with htop:​
htop
  • Provides a graphical view of CPU and memory usage.
2. CPU and Memory Graphs with vmstat:​
vmstat 1 5
  • Reports system performance metrics at 1-second intervals, 5 times.
3. Automating Checks with Cron Jobs:​
crontab -e

Add:

*/5 * * * * free -h >> /var/log/memory_usage.log
  • Logs memory usage every 5 minutes.

Key Takeaways​

Memory Monitoring with free:​

  • Displays RAM and swap memory usage.
  • Use -h for human-readable output.
  • Monitor in real-time using -s.

CPU Load Monitoring with uptime:​

  • Shows system uptime and load averages.
  • Helps analyze CPU performance over time.

Practical Use Cases:​

  • Identify memory leaks or high CPU loads.
  • Troubleshoot slow systems or resource bottlenecks.
  • Automate monitoring using cron jobs.
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