Monitoring with top

The top command provides a real-time view of system processes, CPU usage, and memory consumption.

Basic Usage

top

Understanding the top Display

Header Section

top - 10:00:00 up 1 day, load average: 0.00, 0.01, 0.05
Tasks:   4 total, 1 running, 3 sleeping
%Cpu(s):  0.1 us,  0.1 sy,  0.0 ni, 99.8 id
MiB Mem :  7900.0 total,  4500.0 free,  2000.0 used

• Load average: System load (1, 5, 15 min)
• Tasks: Process counts by state
• CPU: User, system, idle percentages
• Memory: Total, free, used, cached

Process List

Each line shows a process with:

Column	Meaning
PID	Process ID
USER	Owner
%CPU	CPU usage
%MEM	Memory usage
TIME+	Total CPU time
COMMAND	Program name

Interactive Commands

When top is running:

Key	Action
q	Quit
h	Help
k	Kill process
r	Renice (change priority)
M	Sort by memory
P	Sort by CPU
N	Sort by PID
c	Show full command
1	Show per-CPU stats

Exercise: View System Status

Run top to see system status:

top Options

Option	Description
-d N	Update every N seconds
-n N	Exit after N iterations
-u user	Show only user's processes
-p PID	Monitor specific PID
-b	Batch mode (for scripts)

top -d 1           # Update every second
top -n 5           # Run 5 times then exit
top -u root        # Show root's processes
top -p 1234        # Monitor PID 1234

Understanding Load Average

load average: 0.50, 0.75, 1.00
              1min  5min  15min

• < 1.0: System is underutilized
• = 1.0: System is at capacity
• > 1.0: Processes are waiting

For multi-core systems, divide by number of cores.

Memory Information

MiB Mem :   7900.0 total,   4500.0 free,   2000.0 used,   1400.0 buff/cache

• total: Physical RAM
• free: Unused memory
• used: In-use memory
• buff/cache: Disk cache (reclaimable)

Alternatives to top

htop

Enhanced, colorful version:

htop

Features:

• Mouse support
• Color-coded
• Easier process killing
• Tree view

atop

System and process monitor:

atop

Practical Uses

Find Resource Hogs

1. Run top
2. Press M to sort by memory
3. Press P to sort by CPU

Monitor Specific Process

top -p $(pgrep nginx | head -1)

Save top Output

top -b -n 1 > system_report.txt

Key Takeaways

• top shows real-time system stats
• Interactive: use keys to sort and control
• Watch load average for system health
• Press q to quit
• Consider htop for a better interface