Skip to main content

Chapter 4.5 - Processes and Resources

Learning Objectives​

By the end of this chapter, you will be able to:

  • Understand CPU usage by processes
  • Understand memory usage
  • Monitor resources with different tools
  • Identify resource-intensive processes
  • Limit resources

CPU Usage​

CPU Measurement​

# With ps
ps aux --sort=-%cpu | head

# With top
top
# Column %CPU

# With htop
htop
# CPU bars per process

CPU Time​

# Total CPU time used
ps -eo pid,time,comm

# Format: HH:MM:SS
# Example: 01:23:45 = 1h 23min 45s

CPU Load (Load Average)​

# View load
uptime
# Example: load average: 1.25, 0.85, 0.65
# 1 min, 5 min, 15 min

# Interpretation:
# < number of CPUs: OK
# = number of CPUs: Full utilization
# > number of CPUs: Overload

# Number of CPUs
nproc
lscpu | grep "^CPU(s)"

Memory Usage​

Memory per Process​

# With ps
ps aux --sort=-%mem | head

# Readable format
ps aux --sort=-%mem -o pid,%mem,rss,comm | head

# With top
top
# Column %MEM, RES (RSS)

# RSS = Resident Set Size (physical memory)

Types of Memory​

# View details
cat /proc/PID/status | grep -i mem

# VSZ: Virtual Size (virtual memory)
# RSS: Resident Set Size (physical memory)
# Shared: Shared memory

Total Memory​

# Overview
free -h

# Details
cat /proc/meminfo

# By process
ps aux --sort=-%mem | head -10

Monitoring Tools​

vmstat - System Statistics​

# Statistics every second
vmstat 1

# Important columns:
# r: Processes waiting
# b: Blocked processes
# swpd: Swap used
# free: Free memory
# si/so: Swap in/out
# us/sy/id: CPU user/system/idle

iostat - I/O Statistics​

# Install if necessary
sudo apt install sysstat  # Ubuntu/Debian

# I/O statistics
iostat -x 1

# Columns:
# %util: Disk utilization
# r/s, w/s: Reads/writes per second

sar - System Activity Reporter​

# CPU history
sar -u

# Memory history
sar -r

# I/O history
sar -b

# In real-time
sar -u 1 10  # CPU, 1 second, 10 times

Identify Resource-Intensive Processes​

Top 10 CPU​

ps aux --sort=-%cpu | head -11 | tail -10

Top 10 Memory​

ps aux --sort=-%mem | head -11 | tail -10

Processes by User​

# CPU by user
ps aux | awk '{cpu[$1]+=$3} END {for (user in cpu) print user, cpu[user]"%"}'

# Memory by user
ps aux | awk '{mem[$1]+=$4} END {for (user in mem) print user, mem[user]"%"}'

Limit Resources​

ulimit - Per Process Limits​

# View limits
ulimit -a

# Limit virtual memory
ulimit -v 1000000  # 1GB in KB

# Limit processes
ulimit -u 100

# Limit open files
ulimit -n 1024

# Permanent: /etc/security/limits.conf

cgroups - Advanced Control​

# View cgroups
systemd-cgtop

# Limit CPU
systemd-run --slice=my-slice --property=CPUQuota=50% command

# Limit memory
systemd-run --slice=my-slice --property=MemoryLimit=1G command

Summary​

In this chapter, you learned:

CPU: %CPU, CPU time, load average
Memory: %MEM, RSS, VSZ, types of memory
Monitoring: vmstat, iostat, sar for statistics
Identification: ps with sorting for resource-intensive processes
Limits: ulimit, cgroups to control resources

Next Steps​

Chapter 4.6: Jobs and Background Tasks
Module 5: Users and Permissions

Chapter created on: December 2024