Linux system configuration and service management-04-process management

Process Profile

what is a process

• A process is a running instance of an executable program that has been started and consists of:
  • an address space of allocated memory;
  • security attributes, including ownership credentials and privileges;
  • one or more threads of execution of program code;
  • a process state .
• Program: Binary files, static, such as: /usr/bin/passwd, /usr/sbin/useradd
• Process: It is the process of program running, dynamic, with life cycle and running status.

process life cycle

• The parent process copies its own address space (fork) to create a new (child) process structure. Each new process is assigned a unique process ID (PID) for tracking security.
• Any process can create child processes.
• All processes are descendants of the first system process:
• Centos5/6 system process:init
• Centos7 system process:systemd

process state

The cause of the process state

• In a multitasking operating system, each CPU (or core) can only handle one process at a time. While a process is running, its requirements for CPU time and resource allocation are constantly changing, thereby assigning the process a state that changes with the demands of the environment.

process management process

Static view process ps

• PS, is process status, called process status,
  such as the task manager of windows
  

A process as an example

[root@localhost ~]# ps aux |   head  -2
USER        PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root          1      0.0       0.6   128096   6708 ?         Ss    16:20    0:01  /usr/lib/systemd/systemd

• Command parameter description

  • ps a displays all programs under the current terminal
  • ps u Displays program status in a user-oriented format.
  • ps x does not distinguish between terminals.

• Field meaning of ps aux output

  • USER: the user running the process

  • PID: Process ID

  • %CPU: CPU usage

  • %MEM: memory usage

  • VSZ: takes up virtual memory

  • RSS: takes real memory

  • TTY: The terminal the process is running on. terminal type, such pts/0 pts/1 as

  • STAT: process status

     - [常见]
       - R 运行
       - S 睡眠 Sleep
       - T 停止的进程 
       - Z 僵尸进程
       - X 死掉的进程
    

  • START: The start time of the process

  • TIME: The total CPU time occupied by the process, format:分钟：秒

  • COMMAND: process file, process name

process ordering

grammar

ps aux --sort %cpu

• Example
  Sort in descending order by CPU percentage (the minus sign is in descending order)

[root@localhost ~]# ps aux --sort -%cpu
[root@localhost ~]# ps aux --sort %cpu

Process parent-child relationship

grammar

ps -ef

• Example
  View the parent-child relationship of a process. Please observe PID and PPID, PPID is the ID of the parent process

[root@localhost ~]# ps -ef
UID         PID   PPID  C STIME TTY          TIME CMD
root          1      0  0 1月22 ?       00:00:07 /usr/lib/systemd/systemd 
root          2      0  0 1月22 ?       00:00:00 [kthreadd]
root          3      2  0 1月22 ?       00:00:06 [ksoftirqd/0]

Custom display fields (understand)

grammar

ps axo

• example

[root@localhost ~]# ps axo user,pid,ppid,%mem,command |head -3 
root 8310 1 0.1 /usr/sbin/httpd
apache 8311 8310 0.0 /usr/sbin/httpd
apache 8312 8310 0.0 /usr/sbin/httpd

Dynamic view process top

Use the command top

the top half

example

top - 11:45:08 up 18:54,  4 users,  load average: 0.05, 0.05, 0.05
Tasks: 176 total,   1 running, 175 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.0 us,  0.3 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :  3865520 total,  1100000 free,   580268 used,  2185252 buff/cache
KiB Swap:  4063228 total,  4063228 free,        0 used.  2917828 avail Mem 

• line 1
  

• line 2
  

• line 3

• line 4

• line 5
  

the second half

Field introduction (understand)

PID,USER,%CPU,%MEM略
VIRT：virtual memory usage 虚拟内存   # 需要这些内存，但并没有占满。

RES：resident memory usage 常驻内存  # 用了多少内存

SHR：shared memory 共享内存
	- 1、除了自身进程的共享内存，也包括其他进程的共享内存
	- 2、共享内存大小公式：RES – SHR

Top commonly used internal commands

h 或 ?   帮助
M        按内存的使用排序
P        按CPU使用排序
N        以PID的大小排序
<        向前翻页
>        向后翻页
> z 彩色，Z设置彩色，使用数字调整

top skills

• Dynamically view process top, like Windows task manager

[root@localhost ~]# top          //回车，立刻刷新。按z彩色显示，按F，通过光标设置列的顺序。
[root@localhost ~]# top -d 1   //每1秒刷新。
[root@localhost ~]# top -d 1 -p 10126 查看指定进程的动态信息
[root@localhost ~]# top -d 1 -p 10126,1    查看10126和1号进程

Use signal to control process kill

Signal type

Send a signal to a process (kill -l lists all supported signals)

[root@localhost ~]# kill -l 
编号 信号名
1) SIGHUP 重新加载配置
2) SIGINT 键盘中断Ctrl+C，按后发送信号
3) SIGQUIT 键盘退出Ctrl+\，类似SIGINT
9) SIGKILL 强制终止，无条件
15) SIGTERM 终止（正常结束），缺省信号
18) SIGCONT 继续
19) SIGSTOP 暂停
20) SIGTSTP 键盘暂停Ctrl+Z

Signal 9,15

1 Create 2 files and check the terminal number.

[root@localhost ~]# touch file1 file2

2 Through a terminal, open a vim

[root@localhost ~]# vim file1

3 Through another terminal, open a vim

[root@localhost ~]# vim file2

4 Through another terminal, query the two processes

[root@localhost ~]# ps aux |grep vim
root 4362 0.0 0.2 11104 2888 pts/1 S+ 23:02 0:00 vim file1
root 4363 0.1 0.2 11068 2948 pts/2 S+ 23:02 0:00 vim file2

5 Send signal 15 and signal 9 to observe the status of the two terminal programs

[root@localhost ~]# kill  -15 4362
[root@localhost ~]# kill -9 4363
15是走正常退出流程
9是直接杀死，会遗留下来.file2.swp文件，下次打开时会提示存在该文件，需要手动删除

process priority nice

Introduction

Linux process scheduling and multitasking, each CPU can only handle one process at a time point, and use time slice technology to run multiple programs at the same time. There is priority among multiple programs

Priority Ranges and Features

• Priority icon
  
  on the way Nice and PR correspond to the two priorities below

• Two Priorities in the System

  • There are two priorities displayed in top, PR value and nice value
    
    NI: Actual nice value
    PR: primary (+20): The nice level is displayed as being mapped to a larger priority queue, -20 is mapped to 0, +19 Maps to 39

• priority feature

  • The larger the nice value: the lower the priority, such as +19

  • The smaller the nice value: the higher the priority, for example -20

View the nice level of the process

···
[root@localhost ~]# ps axo pid,command,nice --sort=-nice
···

Start processes with different nice levels

• default

When starting a process, it usually inherits the nice level of the parent process, which is 0 by default.

• Manually start different nice

[root@localhost ~]# nice -n -5 sleep 6000 &   # 指定启动进程的nice为-5
[1] 2220
[root@localhost ~]# nice -n -10 sleep 7000 &
[2] 2229
[root@localhost ~]# ps axo command,pid,nice | grep sleep
sleep 6000                    2220  -5
sleep 7000                    2229 -10
grep --color=auto sleep       2233   0

Change the nice level of an existing process

example

Use the shell to change the nice level

1 Create a sleep example program

[root@localhost ~]# sleep 7000 &
[2] 2669

2 Modify his nice value.

[root@localhost ~]# renice -20 2669

2669 (process ID) The old priority is 0, the new priority is -20, observe the old nice value.

Job control jobs (understand)

Introduction

• Job control is a command-line function, also known as running in the background.
• Keyword introduction

fg: foreground   # 前台进程：是在终端中运行的命令，占领终端。

bg：background   # 后台进程：没有控制终端，它不需要终端的交互。看不见，但是在运行。

• Background program control example

1. Observe the phenomenon of occupying the foreground

[root@localhost ~]# sleep 2000

Run a program, the current terminal cannot input. Observe the phenomena that occupy the foreground. Most command line input is no longer valid.
ctrl + cterminate process

2. Run the background program &

[root@localhost ~]# sleep 3000 &

3.ps query all programs.

[root@localhost ~]# ps aux |grep sleep
root 8895 0.0 0.0 100900 556 pts/0 S 12:13 0:00 sleep 3000

4.jobs View the background process.

[root@localhost ~]# jobs
[1]+ Running sleep 3000 &

+,-Represents, fgwhen used, the process that is transferred to the foreground by default. + first, then -

5. Transfer the background program to the foreground.

[root@localhost ~]# fg  1 //将作业1调回到前台

6. The foreground program is immediately transferred to the background ctrl+z, the keyboard is suspended, but the status changes to Stopped

[root@localhost ~]# fg 2
sleep 555
^Z
[2]+  Stopped                 sleep 555

7. Run the stop program

bg 2
[2]+ sleep 555 &
[root@localhost ~]# jobs
[1]-  Running                 nice -n -5 sleep 6000 &
[2]+  Running                 sleep 555 &

8. Eliminate background processes

[root@localhost ~]# kill  %1

Note that "kill 1" is different from "kill %1". The former terminates the process with PID 1, while the latter kills the background program with job number 1.

• Summarize

&          后台运行程序
jobs       查询后台
kill %1    停止后台进程

Virtual file system proc (understand)

Introduction

Virtual file system: collect the status information of the server's own kernel and process operation

# CPU
/proc/cpuinfo
[root@localhost ~]# cat   /proc/cpuinfo

# 内存
/proc/meminfo
[root@localhost ~]# less /proc/meminfo

# 内核
/proc/cmdline
[root@localhost ~]# cat /proc/cmdline