Resource Monitoring

Monitoring your server's resources is essential to understand if the system is running correctly or approaching its limits.

CPU and RAM in real time

`top`: basic monitor (already installed)

top

Useful keys inside top:

P: sort by CPU
M: sort by RAM
k: kill a process (enter the PID)
q: exit

`htop`: advanced monitor (recommended)

# Installation
apt install htop   # Debian/Ubuntu
dnf install htop   # CentOS/AlmaLinux

# Launch
htop

htop shows graphical bars for each CPU core and RAM, and is much more readable than top.

Current RAM usage

free -h

Example output:

              total        used        free      shared  buff/cache   available
Mem:           3.8G        1.2G        800M        45M        1.8G        2.4G
RAM:           4.0G          0B        4.0G

The available column is the one that matters: it's the RAM actually available for new processes.

Current disk usage

df -h

To see only the main partition:

df -h /

Processes consuming the most resources

Top 10 processes using the most CPU:

ps aux --sort=-%cpu | head -11

Top 10 processes using the most RAM:

ps aux --sort=-%mem | head -11

Real-time network traffic

# Install nethogs to see traffic by process
apt install nethogs
nethogs

# Or iftop to see traffic by connection
apt install iftop
iftop

Disk I/O statistics

# Show disk I/O in real time
iostat -x 1

# To install (if not present)
apt install sysstat

System load (load average)

uptime

Example output:

14:32:01 up 5 days,  3:21,  1 user,  load average: 0.12, 0.08, 0.05

The three values are the load average for the last 1, 5 and 15 minutes. A value equal to the number of CPU cores indicates 100% utilization. Higher values indicate that there are processes waiting.

To find out how many cores you have:

nproc

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