Linux System Process Management

What to learn in this chapter

------Process Concepts

------process creation, switchover, and revocation

------Process Scheduling

------Process Classification

------Process Status

------Process Management Tools

Introduction

In the Linux system, the function of the kernel is: process management, file system, network function, memory management, driver, security function, etc., in this many modules, process management is a relatively important link, even if it is not as complex as file system and network functions. In process management, the kernel has a very detailed definition of process creation, switching, revocation, and scheduling.

1. Process and related concepts

<1> Process: a process can be understood as an instance of a program execution with a unique PID to identify it, including executable programs and their associated system resources , such as open files, suspended signals, kernel internal data, Processor state, memory address space, and data segments that contain global variables. From the kernel point of view, a process can also be called a task.

<2> Process Descriptor: There are many things related to the process, such as the PID of the process, the State, the priority of the process, the address space of the process, the files that are allowed to access the process, and so on, the Linux kernel specifically designed a type of task_ struct structure, called the process descriptor . The process descriptor contains all the information about the kernel management process, so that you can know all the information about a process as long as you get the process descriptor of a process.

2. Process creation, switching, and revocation

<1> Process Creation : When the system starts, the kernel is loaded on the CPU, then the kernel creates the first process init (SYSTEMD on CENTOS7), and Init creates a variety of sub-processes through the system fork (), and the processes follow the cow mechanism ( That is to modify the data before allocating memory).

<2> Process switching: process Switching is also known as task switching, context switching. It is a behavior that, in order to control the execution of a process, the kernel suspends the process currently running on the CPU and resumes execution of a previously suspended process.

<3> Undo Process: After the process terminates, the kernel needs to be notified so that the kernel frees the resources owned by the process, including memory, open files, and other resources, such as semaphores

3. Process scheduling

<1> scheduling strategy: The scheduling strategy is a set of rules: decide when and how to choose a new process to run. So define a process's priority to satisfy such a strategy. This strategy is represented by a priority of 0-139.

Real-time Priority: 1-99

No need to adjust, the larger the number, the higher the priority

Static priority: 100-139

Can be adjusted, the smaller the number, the higher the priority

Priority is measured by the Nice value

nice:-20----19, found in task_struct structures

<2> scheduling algorithm: Early Linux, the scheduling algorithm is based on the priority of the process to select the "best" process to execute, its disadvantage is that the time overhead and "the number of running processes". Some scheduling algorithm must satisfy a function relationship, the industry is called Big O

Big O: The relationship between time complexity, timing, and scale. Yes:

O (1), O (Logn), O (n) linear, O (n^2) parabolic, O (2^n)

4. Process Type

Classification criteria for <1> process one:

Daemon: daemon, process initiated during system boot, and terminal-independent process

Foreground process: terminal-related, process initiated through terminal

Note: The two can be converted to each other

Classification criteria for <2> Process II:

Cpu-bound:cpu intensive, non-interactive (graphics)

Io-bound:io intensive, Interactive (operation)

5. Process status

processes that run in memory also have a variety of States

Operating State r:running

Ready state: Readiness

Sleep state

Interruptible s:interruptable

Non-disruptive d:uninterruptable

Stop state t:stopped, paused in memory, but not dispatched unless manually started

Zombie Z:zombie, end process, child process not closed until parent process ends

6. Signal received by the process

<1> common signal: Man 7 signal

1) SIGHUP: No need to close the process and let it reread the configuration file

2) SIGINT: Abort the running process, equivalent to CTRL + C

9) SIGKILL: Kill the Running process

SIGTERM: Terminating a running process

Sigcont: Continue Running

SIGSTOP: Background hibernation

<2> How to specify the signal:

(1) Digital identification of the signal; 1, 2, 9

(2) Signal complete name; SIGHUP

(3) abbreviated name of the signal; HUP

7. Process management Tools

<1>ps aux

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User: Users running the process

PID: Process ID

%cpu: CPU Usage

%MEM: Memory consumption

VSZ: Virtual Memory Set

RSS: Actual memory set

TTY: Terminal information

STAT: Process Status

Start: Process run start time

Time: Runtime

COMMAND: Process Name

You can also display information with specific options

Ps-axo PID, Comm,%cpu,%mem, state, TTY, Euser, Ruser

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The above also proves that the passwd is applicable to suid permissions, although the user is users, but its really effective is the root

<2>uptime

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Boot time

Run time

Number of users logged in

Average load: Refers to the average number of processes running in a queue during a specific time interval

First minute load

Five minute load

Tenth minute load

Note: The average load of 1, 5, 10 minutes is generally no more than 1

Reference value: If the current number of active processes per CPU core is not greater than 3, then the performance of the system is good. If the number of tasks per CPU core is greater than 5, then there is a serious problem with the performance of this machine.

If the Linux host is 1 dual-core CPUs, the load average 6 indicates that the machine is fully used.

<3>top

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Tasks

Total: Number of processes

Running: Number of running processes

Sleeping: Number of dormant state processes

Stopped: Number of stop State processes

Zobie: Number of dead state processes

%CPU (s)

Us:user space: Percentage of CPU occupied by the user

Sy:system: CPU Percentage of kernel space Note: High load: Us:sy=7:3

Ni:nice Modifying the percentage of CPU consumed by nice values

Id:idle Idle CPU Percentage

wa:wait percentage of CPU waiting for IO to complete

Hi:hardware interrupt hard interrupt consumes CPU percentage

Si:software Interrupt Soft Interrupt consumption CPU percentage

St:stole The stolen CPU, such as VMware

Buffer: buffered: Meta data

Cache: Caching: Data

PID: Process Number

User: Process Initiator

Pr:priority: Priority

NI:Nice:nice value

VIRT: Virtual Memory Set

RES: Resident Memory Set

SHR: Shared Memory set

S:status: Status

%CPU:CPU occupancy ratio

%MEM: Memory consumption ratio

Time+: Run duration

COMMAND: Start the process

Sort:

P: As percentage of CPU occupied,%cpu

M: Occupy memory percentage,%MEM

T: Cumulative CPU Duration, time+

The first message shows:

Uptime information: l command

Tasks and CPU information: T command

CPU Display: 1 (digital)

Memory Information: M command

Exit Command: Q

Modify Refresh time interval: s

Terminates the specified process: K

Save File: W

ESC: Exit

View process numbers directly pidof COMMAND or PS aux | grep * *----->kill

<4>htop

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More advanced process management software than top

F1 Help

F2 switching CPU, MEM, swap display mode

F10 exit

Select Process Execution K

<5>vmstat: Viewing disk throughput

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R: Number of processes waiting to run, related to the number of cores

B: Number of processes in non-interruptible sleep state (length of blocked queue)

Swap

SI: Data rate for swapping into memory from disk (KB/S)

So: Data rate from memory swap to disk (KB/S)

Io:

BI: The rate at which data is read into memory from a block device (KB/S)

Bo: The rate at which data is saved to block to memory

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Server side: glances-s-B IP

Client side: Glances-c IP <7>dstat

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Disk reads and writes can be tested via DD If=/dev/sdb Of=/dev/zero

Network monitoring can be tested by Ping-f ip-s 65507.

This article is from the "Linux_home" blog, make sure to keep this source http://dmwing.blog.51cto.com/11607397/1847408

Linux System Process Management