[Linux] Process management process

Process management

1. Basic introduction to the process

1. In Linux, each executed program and code becomes a process. Each process is assigned an ID number. A Simple Explanation of Processes and Threads
2. Each process corresponds to a parent process, and the parent process can replicate multiple child processes.
3. Each process may exist in two forms. Foreground and background, the foreground process is the operation that can be performed on the current screen; the background process is actually operating, but because the process cannot be seen on the screen, it is usually executed in the background mode.
4. General system services exist in the form of background processes, and because the processes cannot be seen on the screen, they are usually executed in the background mode.

2. Display the process executed by the system

$$ps -aux$$

ps [选项]: Displays the status of the current process (process).

Options

parameter	Function
-a	Display all process information of the current terminal
-u	Display process information in user format
-x	Display the parameters of the background process running
-e	show all processes
f	full format

Example

1. View progress

   • [root@wcl ~]# ps -aux|more
     USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
     root         2  0.0  0.0      0     0 ?        S    4月27   0:00 [kthreadd]
     root         3  0.0  0.0      0     0 ?        S    4月27   0:00 [ksoftirqd/0]
     root         5  0.0  0.0      0     0 ?        S<   4月27   0:00 [kworker/0:0H]
     ……省略部分结果

   • Pay attention to the second line above; let's introduce the specific meaning of each column name in it

   • column name	meaning
     USER	user name
     PID	Process ID
     %CPU	The percentage of CPU used by the process
     %MEM	The percentage of physical memory used by the process
     VSZ	The size of virtual memory occupied by the process (KB)
     RSS	Physical memory size occupied by the process (KB)
     TTY	terminal used
     STAT	Process status; S: sleep; R: running, etc.
     START	start time of the process
     TIME	CPU time, which is the total time the process uses the CPU
     COMMAND	Commands and parameters used to start the process

     ​

2. Display all current processes in full format, and see the parent process of the process

   • ps -ef | more

   • [root@wcl ~]# ps -ef |more
     UID        PID  PPID  C STIME TTY          TIME CMD
     root         3     2  0 4月27 ?       00:00:00 [ksoftirqd/0]
     root         5     2  0 4月27 ?       00:00:00 [kworker/0:0H]
     ... ...//省略剩余结果

   • Note: PID is the process ID; PPID: is the parent process ID

3. View sshd process

   • ps -ef | grep sshd

     ​

3. Terminate the process kill and killall

You want to stop the process halfway, or because the process consumes a lot of system resources. We use the kill command to accomplish this task.

$$kill$$
kill [选项] 进程号 : kill process by process number

killall 进程名称: Kill process by process name, wildcards are also supported

Common options

Options	Function
-9	Force the process to stop immediately

Example

1. Kick off an illegal login user

   • [root@wcl ~]# ps -aux
     USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
     root         2  0.0  0.0      0     0 ?        S    4月27   0:00 [kthreadd]
     root     16628  0.0  0.0 150424  5860 ?        Ss   17:26   0:00 sshd: root@pts/3
     root     16630  0.0  0.0 116316  2908 pts/3    Ss   17:26   0:00 -bash
     root     16651  0.0  0.0 189604  2364 pts/3    S    17:26   0:00 su jack
     jack     16652  0.0  0.0 116328  2928 pts/3    S+   17:26   0:00 bash

   • Note: we kick user jack out here

   • kill 16651

     At this moment, the following paragraph will appear in the jack login window

     [jack@wcl root]$ 
     Session terminated, killing shell... ...已杀死。
     [root@wcl ~]# 

2. Force kill terminal 199

   • 
kill -9 199


Fourth, view the process tree pstree

You can view the process information more intuitively; here I don't have this command in my system for the time being, and I won't record it for the time being.

Installation instructions After
minimal installation of centos, use pstree to display the process tree, prompting that there is no such command.
It turns out that it is not installed, and psmisc needs to be installed
yum install psmisc

Improve it later! ! !

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to be continued… …

5. Service Management

Six, dynamic monitoring process