8-Linux process management

basic introduction

In Linux, each executed program is called a process, and each process is assigned an ID number (PID)

Each process may exist in two ways, foreground and background

Generally, the services of the system exist in the form of background processes, and they will be resident in the system until the system is shut down.

Display the processes executed by the system

Basic introduction to ps command

ps (process show) is used to display what is currently being executed in the system and their execution status.

ps [选项]

optional options

1. ps -a displays all process information of the current terminal
2. ps -u displays process information in user format
3. ps -x displays the parameters of the background process running

Generally speaking, the combined use is:ps -aux

4. ps -e: show all current processes
5. ps -f: full format

Terminate process kill and killall

basic grammar

• kill [选项] 进程号
  • Kill/terminate process by process ID
  • options
    • -9Indicates to force the process to stop immediately
• killall 进程名称
  • kill process by process name

View process tree pstree

yum install psmisc❗️: If it shows that there is no such command, you can install this command in cenos .

Basic syntax:pstree [选项]

You can view process information more intuitively

Common options

• -p displays the pid of the process
• -u displays the user the process belongs to

service service management

service introduction

The essence of a service (service) is a process, but the process runs in the background. It usually listens to a certain port and waits for requests from other programs.

Therefore, daemons are also called daemons.

service management command

• service 服务名 [start|stop|restart|status]
• After cenos7, many services no longer use service to manage, but use systemctl
• ⭐️The services managed by the service command /etc/init.dare viewed in ([[1-Linux directory structure #^f9a9d2|linux /etc directory]])

chkconfig command

Through the chkconfig command, you can set self-start/shutdown for each run level of the service

In other words, the self-starting and closing of the service is for different machine operation levels

Display the services supported by the chkconfig command:chkconfig --list

Use the chkconfig command

Format:chkconfig --level 级别 服务名 on/off

![[3-Linux practical operation#specified run level]]

❗️: When using chkconfig to reset the self-start and shutdown of the service at different levels, the machine needs to be restarted to take effect.

systemctl management commands

basic instructions

systemctl [start|stop|restart|status] 服务名

⭐️: The services managed by the systemctl/usr/lib/systemd/system command are viewed in

![[1-Linux directory structure #^050dfd]]

systemctl sets the self-starting state of the service

• View service startup status
  • systemctl list-unit-files
• Set the service to start at boot
  • systemctl enable 服务名
• Close the service and start it
  • systemctl disable 服务名
• Query whether a service is self-starting
  • systemctl is-enabled 服务名

example

Check the firewalld service supported by systemctl

It is found that firewalld.service exists

Then you can control and view the

• systemctl status firewalld
• systemctl stop firewalld
• systemctl start firewalld

Open or close the specified port

• open port
  • firewall-cmd --permanent --add-port=端口号/协议
• close port
  • firewall-cmd --permanent --add-port=端口号/协议
• Reload to take effect
  • firewall-cmd --reload
• Query whether the port is open
  • firewall-cmd --query-port=端口/协议

In win, you can telnet IP地址 端口test whether the port of a certain host is open by

Dynamic monitoring process

basic usage

top [选项]

Both "top" and "ps" are commands used in Unix and Unix-like systems to view information about processes running on the system. The difference between them:

1. Function
   • top is a dynamic process monitoring tool, which displays real-time process information running in the system , including CPU usage, memory usage, etc.
   • ps is a static process viewing tool, which displays the process information in the current system at one time and will not be updated in real time.
2. Display method
   • top displays process information interactively, dynamically sorts and filters processes, and updates the display in real time.
   • ps displays process information on the command line, and you need to use different options to specify the information to be displayed.

Option Description

• -d 秒数: Specify the top command to update every few seconds, the default is 3s
• -i: use top to not show any idle or zombie processes
• -p: Only monitor the status of a process by specifying the monitoring process ID

Interactive operation in top

operate	Function
P	Sort by CPU usage, the default is this option
M	Sort by memory usage
N	Sort by PID
u	Enter a username to monitor a specific user
k	Enter the ID number of the process to be terminated to terminate the specified process
q	quit

Check network status

View system network status netstat

• basic grammarnetstat [选项]
  • View system network status
  • Option Description
    • -anArrange the output in a certain order
    • -pShow which process is calling

Detect host connection command ping

Check whether the connection to the remote host is normal