Linux Process managementment - Geek Tutorial Network

1. Process Overview

A process is an execution instance of a program and the basic unit for operating system resource allocation and scheduling. In Linux systems, each run program creates one or more processes, which occupy system resources (such as CPU, memory, disk I/O, etc.). Understanding process concepts and management methods is crucial for Linux system administration and performance optimization.

1.1 Process Lifecycle

Creation: New processes are created through the fork() system call.
Ready: The process is ready to run, waiting for CPU allocation.
Running: The process is executing on the CPU.
Blocked: The process is waiting for an event to complete (such as an I/O operation).
Termination: The process has completed execution or been terminated.

1.2 Process States

R (Running): The process is run or waiting in the ready queue.
S (Sleeping): The process is in an interruptible sleep state, waiting for an event to complete.
D (Disk Sleep): The process is in an uninterruptible sleep state, usually waiting for an I/O operation to complete.
Z (Zombie): The process has terminated, but the parent process has not yet reclaimed its resources.
T (Stopped): The process has been paused.
X (Dead): The process is dead, which is a transient state and usually not visible in process lists.

2. Process Viewing Commands

Linux provides multiple commands for viewing process information in the system, which can help us understand process status, resource using, and more.

2.1 ps Command

ps (Process Status) command is used to display process information in the current system.

# View processes in current terminal
ps

# View all processes
ps aux

# View all processes in tree structure
ps -ef --forest

# View processes of specific user
ps -u username

# View specific process
ps -p PID

# Sort by CPU using
ps aux --sort=-%cpu

# Sort by memory using
ps aux --sort=-%mem

# View thread information of process
ps -L PID

# Display detailed process information
ps -ef | grep process_name

2.2 top Command

top (Table of Processes) command is used for real-time monitoring of process status and resource using in the system.

# Start top command
top

# Run top in batch mode
top -b

# Set top refresh interval (seconds)
top -d 1

# Show only processes of specific user
top -u username

# Show only processes with specific PIDs
top -p PID1,PID2

# Sort by CPU using
top -o %CPU

# Sort by memory using
top -o %MEM

# Show thread information
top -H

# Interactive keys in top
# h: Show help information
# k: Terminate specified process
# r: Modify process priority
# q: Exit top
# 1: Show using of all CPU cores
# M: Sort by memory using
# P: Sort by CPU using
# T: Sort by cumulative run time
# c: Show complete command line

2.3 htop Command

htop is an enhanced version of top, providing a more user-friendly interface and more features.

# Install htop
sudo apt install htop  # Debian/Ubuntu
sudo yum install htop  # CentOS/RHEL

# Start htop
top

# Interactive keys in htop
# F1: Show help information
# F2: Set up htop
# F3: Search processes
# F4: Filter processes
# F5: Display in tree structure
# F6: Select sort method
# F7: Decrease process priority
# F8: Increase process priority
# F9: Terminate process
# F10: Exit htop
# Spacebar: Mark process
# u: Show processes of specific user
# l: Show files opened by process
# s: Show system calls of process

2.4 pgrep and pkill Commands

pgrep command is used to find processes by process name or other attributes, and pkill command is used to terminate processes by process name or other attributes.

# Find processes with specific name
pgrep process_name

# Find processes of specific user
pgrep -u username

# Find processes and show complete command line
pgrep -l process_name

# Find processes and show process ID and complete command line
pgrep -a process_name

# Terminate processes with specific name
pkill process_name

# Terminate processes of specific user
pkill -u username

# Terminate processes of specific terminal
pkill -t terminal

2.5 pidof Command

pidof command is used to find the process ID of a specified program.

# Find process ID of specified program
pidof program_name

# Find process ID of specified program, separated by commas
pidof -c program_name

# Find process ID of specified program, separated by spaces
pidof -s program_name

3. Process Control Commands

Linux provides multiple commands for controlling process execution, including starting, terminating, pausing, and resuming processes.

3.1 kill Command

kill command is used to send signals to processes, most commonly to terminate processes.

# Terminate process with specified PID
kill PID

# Force terminate process
kill -9 PID

# Send SIGTERM signal to process (default)
kill -15 PID

# Send SIGHUP signal to process
kill -1 PID

# Send SIGINT signal to process
kill -2 PID

# Send SIGSTOP signal to process
kill -19 PID

# Send SIGCONT signal to process
kill -18 PID

# Terminate all processes with specified name
kill $(pgrep process_name)

# View available signals
trap -l
kill -l

3.2 killall Command

killall command is used to terminate processes by process name.

# Terminate all processes with specified name
killall process_name

# Force terminate all processes with specified name
killall -9 process_name

# Terminate all processes matching specified name (case insensitive)
killall -I process_name

# Terminate all processes of specified user
killall -u username

# Only terminate processes run longer than specified time
killall -o 10m process_name

# Only terminate processes run less than specified time
killall -y 10m process_name

3.3 pkill Command

pkill command is used to terminate processes by process name or other attributes.

# Terminate all processes with specified name
pkill process_name

# Force terminate all processes with specified name
pkill -9 process_name

# Terminate all processes matching specified pattern
pkill -f pattern

# Terminate all processes of specified user
pkill -u username

# Terminate all processes of specified terminal
pkill -t terminal

3.4 nice and renice Commands

nice command is used to set process priority, and renice command is used to modify the priority of run processes.

# Start process with specified priority
nice -n 10 command

# Start process with highest priority
nice --19 command

# Modify priority of run process
renice 10 -p PID

# Modify priority of all processes of specific user
renice 5 -u username

# Modify priority of all processes of specific group
renice 0 -g groupname

4. Job Control

Job control refers to managing the execution of multiple processes in a single terminal session, including placing processes in foreground or background execution, pausing and resuming processes, etc.

4.1 Basic Job Control Commands

# Start process in background
command &

# Pause current process (Ctrl+Z)
# Then can use fg or bg commands to continue execution

# View all jobs
jobs

# Move background job to foreground
fg %job_id

# Continue paused job in background
bg %job_id

# Terminate background job
kill %job_id

# Run process in background and ignore SIGHUP signal
nohup command &

# Run process in background and redirect output to file
command > output.log 2>&1 &

# Run process in background and detach from terminal
setsid command

# Create session using screen or tmux
screen
# or
tmux

4.2 screen Command

screen command is used to create multiple sessions, each of which can run different commands and can be switched between different terminals.

# Install screen
sudo apt install screen  # Debian/Ubuntu
sudo yum install screen  # CentOS/RHEL

# Create new session
screen

# Create named session
screen -S session_name

# List all sessions
screen -ls

# Attach to session
screen -r session_name

# Detach session (Ctrl+A, d)

# Terminate session
exit

# Force terminate session
screen -S session_name -X quit

4.3 tmux Command

tmux is a terminal multiplexer, similar to screen but providing more features.

# Install tmux
sudo apt install tmux  # Debian/Ubuntu
sudo yum install tmux  # CentOS/RHEL

# Create new session
tmux

# Create named session
tmux new -s session_name

# List all sessions
tmux ls

# Attach to session
tmux attach -t session_name

# Detach session (Ctrl+B, d)

# Terminate session
exit

# Force terminate session
tmux kill-session -t session_name

# Create new window in session (Ctrl+B, c)

# Switch between windows (Ctrl+B, 0-9)

# Create new pane in session (Ctrl+B, % or Ctrl+B, ")

# Switch between panes (Ctrl+B, arrow keys)

5. System Resource Monitoring

System resource monitoring is an important part of Linux system administration, which can help us understand the system's run status and timely discover and solve problems.

5.1 System Load Monitoring

# View system load
uptime

# View system load and process status
top

# View historical system load records
mpstat

# View load of each CPU core
mpstat -P ALL

5.2 Memory Usage Monitoring

# View memory using
free -h

# View detailed memory using information
cat /proc/meminfo

# View process memory using
top -o %MEM

# View memory using of specific process
pmap PID

# View process memory map
cat /proc/PID/maps

5.3 Disk I/O Monitoring

# View disk I/O status
iostat

# View detailed disk I/O information
iostat -x

# View I/O status of specific disk
iostat -x /dev/sda

# Real-time monitor disk I/O
iotop

# View I/O status of processes
iotop -p PID

# View disk using
df -h

# View directory size
du -h directory

5.4 Network I/O Monitoring

# View network interface statistics
netstat -i

# View network connection status
netstat -tuln

# View network interface traffic
ifconfig

# Real-time monitor network traffic
tcpdump

# Real-time monitor network connections and traffic
netstat -ant

# View process network connections
lsof -i

# View network connections of specific process
lsof -i -p PID

5.5 Comprehensive Monitoring Tools

# Install sar
sudo apt install sysstat  # Debian/Ubuntu
sudo yum install sysstat  # CentOS/RHEL

# View CPU using
sar -u

# View memory using
sar -r

# View disk I/O status
sar -d

# View network I/O status
sar -n DEV

# View system comprehensive performance
tuned-adm list

# Install and use atop
sudo apt install atop  # Debian/Ubuntu
sudo yum install atop  # CentOS/RHEL

# Start atop
atop

6. Process managementment Practice

6.1 Case Objective

Monitor process status in the system, identify and handle processes that occupy excessive resources, and ensure stable system operation.

6.2 Implementation Steps

6.2.1 Monitor System Load

# View system load
uptime

# Real-time monitor system status
top

6.2.2 Identify Processes Occupying Excessive Resources

# View processes with highest CPU using
ps aux --sort=-%cpu | head -10

# View processes with highest memory using
ps aux --sort=-%mem | head -10

# View processes with highest disk I/O using
iotop -o -b | head -10

6.2.3 processing Processes Occupying Excessive Resources

# Terminate process occupying excessive resources
kill PID

# Force terminate process
kill -9 PID

# Modify process priority
renice 10 -p PID

# Run process in background
command > output.log 2>&1 &

# Run long-term task using screen or tmux
screen -S task_name
# Then run command in screen session
# Press Ctrl+A, d to detach session

6.2.4 Monitor Process Status

# View process status
ps -p PID -o pid,ppid,state,command

# View detailed process information
cat /proc/PID/status

# View files opened by process
lsof -p PID

# View network connections of process
netstat -antp | grep PID

7. Interactive Exercises

Exercise 1: Process Viewing

Perform the following operations:

1. Use ps command to view all processes in the system.
2. Use ps command to view processes of specific user.
3. Use top command to real-time monitor process status in the system.
4. Use pgrep command to find processes with specific name.
5. Use pidof command to find process ID of specific program.

Exercise 2: Process Control

Perform the following operations:

1. Start a long-run process (such as sleep 3600).
2. Use kill command to terminate the process.
3. Start multiple processes with the same name.
4. Use killall command to terminate all these processes.
5. Start processes with different priorities and observe their execution.

Exercise 3: Job Control

Perform the following operations:

1. Start a process in the background.
2. Use jobs command to view job list.
3. Move background job to foreground.
4. Pause foreground process, then move it to background to continue execution.
5. Use nohup command to start a process so it continues run after terminal closure.

Exercise 4: System Resource Monitoring

Perform the following operations:

1. Use iostat command to view disk I/O status.
2. Use free command to view memory using.
3. Use netstat command to view network connection status.
4. Use sar command to view system comprehensive performance.
5. Identify the process that occupies the most resources in the system and analyze the reason.

1. Process Overview

1.1 Process Lifecycle

1.2 Process States

2. Process Viewing Commands

2.1 ps Command

2.2 top Command

2.3 htop Command

2.4 pgrep and pkill Commands

2.5 pidof Command

3. Process Control Commands

3.1 kill Command

3.2 killall Command

3.3 pkill Command

3.4 nice and renice Commands

4. Job Control

4.1 Basic Job Control Commands

4.2 screen Command

4.3 tmux Command

5. System Resource Monitoring

5.1 System Load Monitoring

5.2 Memory Usage Monitoring

5.3 Disk I/O Monitoring

5.4 Network I/O Monitoring

5.5 Comprehensive Monitoring Tools

6. Process managementment Practice

6.1 Case Objective

6.2 Implementation Steps

6.2.1 Monitor System Load

6.2.2 Identify Processes Occupying Excessive Resources

6.2.3 processing Processes Occupying Excessive Resources

6.2.4 Monitor Process Status

7. Interactive Exercises

Exercise 1: Process Viewing

Exercise 2: Process Control

Exercise 3: Job Control

Exercise 4: System Resource Monitoring

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