nctuns的GUI手册

【实例简介】
vanet极好的仿真工具nctuns的GUI应用手册
l。 Introduction immediately knows how to configure and operate a simulated network in NCTUns,(2)Conversely, since the configuration and operation of simulated networks in elcome to the gui user manual of nctuns -a NCTUns are exactly the same as those for real-life IP high-fidelity and extensible network simulator and networks, NCTUns can be used as a training tool to educate emulator. In this introduction we will briefl people how to configure and operate a real-life IP network introduce the capabilities and features of NCTUns. To help In NCTUns, many valuable real-life UNIX network config- users understand how NCTUns works the high-level uration tools(e.g, route, ifconfig, netstat) and performance structure of NcTUns will be presented in detail. Some monitoring tools(e.g. ping, tcpdump traceroute)can be screenshots are shown in this chapter to let readers get a feel directly run on a simulated network to configure and monitor ofNctuns a simulated network Seamless Integration of Emulation and simulation Capabilities and features NCTUns can be turned into an emulator easily. In an NCTUns uses a novel kernel-reentering simulation method emulation, nodes in a simulated network can exchange real ology [1,2,3,4,5,6,7,8]. As a result, it provides several packets with real-world machines via the simulated network unique advantages that cannot be easily achieved by tradi- That is, the simulated network is seamlessly integrated with tional network simulators. In the following, we briefly the real-life network so that simulated nodes and real-life explain its capabilities and features nodes can exchange their packets across the integrated High-Fidelity Simulation Results simulated and real-life networks. This capability is very useful for testing the functions and performances of a real- NCTUns directly uses the real-life Linux's TCP/IP protocol life device(e.g, a VoIP phone)under various network condi stack to generate high-fidelity simulation results. By using tions. In a NCTUns emulation case. an external real-lite the novel kernel re-entering simulation methodology. a real- device can be a fixed host. a mobile host or a router life UNIX(e.g, FreeBSD or Linux)kernels protocol stack NCTUns supports distributed emulation of a large network is directly used to generate high-fidelity simulation results over multiple machines. If the load of an emulation case is Reusing All Real-Life Application Programs too heavy so that it cannot be carried out in real time on a single machine, this approach can simultaneously use the In NCTUns, all real-life existing or to-be-developed UNIX CPU cycles and main memory of multiple machines to carry application programs (e.g. the p2P Bit Torrent application) nulation case in real time. more information can be run up on a node in a simulated network This about this useful feature is available in a later chapter named provides several unique advantages: (1)These real-life Distributed emulation application programs generate realistic network traffic to drive simulations, which leads to more convincing results lligh Simulation Speeds and Repeatable simulation Results than using the artificial traffic generated by some simple NCTUns combines the kernel re-entering simulation toy'functions,(2)The performances of these real-life methodology with the discrete event simulation method applications under various network conditions can be ology. As a result, it executes simulations quickly NCTUns evaluated and then improved before they are released to the modifies the process scheduler of the Linux kernel to public. For example, a network-game application can be first accurately control the execution order of the simulation tested, evaluated, and improved on nctUns before it is engine process and all involved real-life application released to the public. (3)The applications developed at the processes. If the same random number seed is used for a simulation study stage can be readily used and deployed on simulation case, the simulation results are repeatable across real-life uNiX machines when the simulation study is different runs finished. This will save time and effort significantly Support for Various Important Networks Same Configuration and operation as for Real-Life Networks NCTUns simulates ethernet-based ip networks with fixed In NCTUns, the contiguration and operation for a simulated nodes and point-to-point links. It simulates IEEE802.11 network are exactly the same as those for a real-life IP (a)(b)wireless Lan networks, including both the ad-hoc and network. This provides two advantages:(1)If a user knows infrastructure modes. It simulates gprs cellular networks. It how to configure and operate a real-life IP network, he(she) simulates optical networks, including traditional circuit structure mode wireless interface, ITS cars each equipped switching optical network and more advanced optical burst with a GPRS wireless interface, ITS cars each equipped with switching(OBS)networks a dvB-RCst wireless interface, ITS cars each equipped It simulates IEEE 802. 11(b) wireless mesh networks. IEEE with a 802. 16(e)intertace, ITS On-Board Unit (oBU)each 802.11(e)Qos networks, tactical and active mobile ad hoc equipped with a 802.11(p) interface, and ITs cars each networks. and wireless networks with directional and equipped with all of these six different wireless interfaces. steerable antennas. It simulates 802. 16(d) WiMAX For mobile nodes each equipped with multiple heteroge networks including the pmp and mesh modes It simulates neous wireless interfaces, it simulates (1)a traditional 802.16(e) mobile WiMAX PMP networks. It simulates mobile node that moves on a pre-specified path(e. g, random 802.16( transparent mode and non-transparent mode rela waypoints), and(2) an ITs car that automatically move WiMAX networks. It simulates the DVB-Rcs satellite (auto-pilot) on a constructed road networks for a GEO satellite located 36,000 Km above the NCTUns provides more realistic wireless physical modules earth. It simulates 802.11(p)1609 vehicular networks, which that consider the used modulation scheme, the use is an amendment to the 802. 11-2007 standard for highly encoding/decoding schemes, the received power level, the mobile environment. Over this platform, one can easily noise power level, the fading effects, and the derived BeR develop and evaluate advanced V2v (vehicle-to-vehicle) ( Bit Error Rate) for 802.11(a),802.11(b), 802. 11(p), GPRS and V2I (vehicle-to-infrastructure) applications in the ITs 802.16(d) fixed WIMAX, 802.16(e) mobile WiMAX, (Intelligent Transportation Systems)research field 802.16(relay WiMAX, and DVB-RCST satellite networks It simulates multi-interface mobile nodes equipped with These advanced physical-layer modules can generate more realistic results but at the cost of more cpu time required to multiple heterogeneous wireless interfaces. This type of mobile nodes will become common and play an important finish a simulation. Depending on the tradeoff of simulation role in the real life because they can choose the most cost- speed vs result accuracy, a user can choose whether to use effective network to connect to the internet at any time and the basic simple physical-layer modules or the advanced It any location hysical-layer modules Support for Various Networking Devices NCTUns supports omnidirectional and steerable antennas with realistic antenna gain patterns. The antenna gain data NCTUns simulates common networking devices such as are stored in a table file and the content of the file can be Ethernet hubs, switches, routers, hosts, IEEE 802.11(b) changed (even time-varying)casily if he(she)would like to wireless access points and interfaces, IEEE 802.11(a) use his/her own antenna gain patterns wireless access points and interfaces, etc. For optical Support for Various Network Protocols networks, it simulates optical circuit switches and optical burst switches, WDM optical fibers, and WDM protection NCTUns simulates various protocols such as IEEE 802. 3 rings. F'or Diffserv Qos networks, it simulates Diffserv CSMA/CD MAC. IEEE l1(a)(b(ep) csma/Ca boundary and interior routers for Qos provision For GPRS s MAC,the learning bridge protocol used by switches, the networks, it simulates GPrs phones, GPRS base stations spanning tree protocol used by switches, IP, Mobile IP, rip SGSN, and ggsn devices. For 802. 16(d) WiMAX Ospf. udP Tcp Http Ftp Telnet etc. It simulates the networks, it simulates the PMP-mode base stations(BS)and DiffServ Qos protocol suite, the optical light-path setup Subscriber Stations (SS) and the mesh-mode base stations protocol, the RTP/RTCP/SDP protocol suite. It simulates the and Subscriber Stations (Ss). For 802. 16(e) WiMAx IEEE 802. 16(d)(e)()WiMAX PMP protocol suites and the networks, it simulates the PMP-mode base stations(BS)and 802. 16(d) mesh mode protocol suite. It simulates the DVB Subscriber Stations(SS). For 802.16G transparent mode RCST protocol suite and non-transparent mode WiMAX networks, it simulates Highly-Integrated and Professional GUI Environment the base stations(BS), relay stations(RS), and mobile NCTUns provides a highly-integrated and professional gUl stations(MS). For dvB-Rcs network, it simulates the geo satellite, Network Control Center(NCC), Return Channel environment in which a user can easily conduct network Satellite Terminal (RCST), feeder, service provider, traffic simulations. The NcTUns gui program is capable of gateway For wireless vehicular networks, it simulates ITS Drawing network topologies cars each equipped with an 802. 11(b) ad hoc-mode wireless Configuring the protocol modules used inside a nod interface, ITS cars each equipped with an 802. 11(b) infra- Configuring the parameter values used inside a simulation throughput when multiple machines are protocol module available. Because the components of NCTUns use Inter- Specifying the initial locations and moving paths of Process Communication (IPC, that is, sockets) to commu mobile nodes nicate, they can also be run on the same machine. This is Plotting network performance graphs called the"single-machine"mode. ) In fact, because most people have only one computer to run their simulations, the Playing back the animation of a logged packet transfer single-machine" mode is the default mode after the race NCTUns package is installed. Switching between these two Pasting a map graph on the background of the network modes is very easy and requires changing only one configu- topology ration option in a file Constructing a road network for wireless vehicular network simulations More Components and Architecture of NCTUns Popular Operating system Support NCTUns adopts a distributed architecture. It is a system comprising eight components NCTUns runs on Linux operating systems. The linux distri bution that NCTUns 6.0 currently supports is Red-Hat I The first component is the gui program by which a user Fedora 11, whose Linux kernel version currently is 2.6.28.9 edits a network topology, configures the protocol modules Other linux distributions such as debian can also be used inside a network node, specifies mobile nodes' initial supported with some minor operating system configuration location and moving paths, plots performance graphs changes plays back the animation of a packet transfer trace, etc Open-System Architecture 2 The second component is the simulation engine program, which provides basic and useful simulation services(e.g By using a set of well-defined module APIs that are provided event scheduling, timer management, and packet manipu- by the simulation engine, a protocol module developer can ation, etc. ) to protocol modules. We call a machine on casily implement his(her )own protocol and integrate it into which a simulation engine program resides a"simulation the simulation engine. Details about adding a new protocol server module to the simulation engine are presented in the "the 3 The third component is the set of various protocol Protocol Developer Manual for the NCTUns 6.0 Network modules, each of which implements a specific protocol or Simulator and emulator function (e.g. packet scheduling or buffer management) Distributed architecture for remote and concurrent simula- all protocol modules are C++ classes and are compiled and linked with the simulation engine program By using a distributed architecture, each component of 4 The fourth component is the simulation job dispatcher NCTUns can be run on a separate machine. ( This is called program that can simultaneously manage and use multiple the multi-machine"mode. )As such, the machine that runs simulation servers to increase the aggregate simulation the gui program can be different from the machine that runs throughput. It can be run on a separate machine or on a the simulation engine. This capability sometimes can have simulation server an advantage, When simulating a very large case with hundreds of mobile nodes the gui will consume many CPu 5 The fifth component is the coordinator program On every cycles to draw the movements of these mobile nodes durin simulation server, thecoordinator"program must be run up The coordinator should be alive as long as the the simulation. However this will leave few cpu cycles for simulation server is alive. when a simulation server is the simulation engine to simulate the network protocols. To powered on and brought up, the coordinator must be run overcome this performance problem, using the multi up. It will register itself with the dispatcher to join in the machine mode to run the gui program and the simulation dispatchers simulation server farm. Later on, when the engine on two different machines is a good solution status(idle or busy) of the simulation server changes, it will notify the dispatcher of the new status. This enables In addition, with the job dispatcher program, multiple the dispatcher to choose an available simulation server simulation engine machines can be managed by a single job from its simulation server farm to service a job dispatcher. This architecture design can easily support remote and concurrent simulations which increases the tota When the coordinator receives a job from the dispatcher, it forks a simulation engine process to simulate the specified network and protocols. It may also fork several real-life Simulation Server application program processes specified in the job. These GUIBoston processes are used to generate traffic in the simulated i Simulation network Server NCTU Rome When the simulation engine process is alive, the coordi Simulation Dispatcher nator communicates with the dispatcher and the guI Server■ program on behalf of the simulation engine process. For I Simulation GUI)Paris example, the simulation engine process needs to periodi cally send its current simulation clock to the gui program This is done by first sending the clock information to the Simulation Background GUI) Tokyo coordinator and then asking the coordinator to forward this Job queue information to the GuI program. This enables the GUI user to know the progress of the simulation Simulation service center During a simulation the gui user can also on-line set o Kernel modifications get an object's value(e. g, to query or set a switch's current switch table). Message exchanges that occur between the A Simulation server == Simulation Engine Protocol modules simulation engine process and the gui program are all Coordinator relayed via the coordinator The distributed architecture of NcTUns 6 The sixth component is the kernel patches that need to be made to the kernel source code so that a simulation engine In addition to the above "multi-machine"?mode. another process can run on a UNIX machine correctly. Currently mode called the"single machine"mode is supported. In such NCTUns 6.0 runs on red-Hat's Fedora ll which uses the a mode, all of these components are installed and run on a Linux 2.6.28.9 kernel single machine. Although in this mode different simulation 7 The seventh component is the various real-life user-level jobs cannot be run concurrently on different machines, since application programs. Due to the novel kernel-reentering most users have only one machine to run their simulations simulation methodology, any real-life existing or to-be developed application program can be directly run up on a this mode may be more appropriate for them. In fact, it is the default mode after the nctuns package is installed simulated network to generate realistic network traffic 8 The eighth component is the various user-level daemons that are run up for the whole simulation case. For example, Some screenshots of nctun NCTUns provides RIP and ospf routing daemons. By running these daemons, the routing entries needed for a To give readers a quick idea about what the GUI Simulated network can be constructed automatically. As environment looks like. some screenshots of NCTUns are another example, NCTUns provides and automatically shown beloy runs up several emulation daemons when it is turned into Starting Screen an emulator Every time when a user launches the GUI program, the following starting screen will pop up Due to this distributed design, a remote user can submit his Cher) simulation job to a job dispatcher, and the dispatcher will then forward the job to an available simulation server for execution. The server will process(simulate) the job and later return the results back to the remote gui program for NCTUns 6.0 further analyses. This scheme can easily support the server farm model in which multiple simulation jobs are performed concurrently on different simulation servers. The following figure shows the distributed architecture of the nctUns Topology editor Performance monitor The topology editor provides a convenient and intuitive way The performance monitor can easily and graphical to graphically construct a network topology. A constructed generate and display plots of some monitored performance network can be a fixed wired network or a mobile wireless metrics over time. Examples include a links utilization or a network. For ITS applications, a road network can also be TCP connection's achieved throughput Because the format constructed. Due to the user-friendly design, all gUl opera of its input data log file uses the general two-column(x, y) tions can be performed easily and intuitively. format and the data is in plain text, the performance monitor can be used as an independent plotting tool wwww 25E ,“时 知忐即即涉日希%94么 aD ER P …a” 只只p‖ 0mmm巴,函 只只间Ⅱ The topology editor of NctUns The performance monitor of NCTUns Attribute dialog box Node editor A network device(node) may have many attributes. Setting and modifying the attributes of a network node can be easily The node editor provides a convenient environment in which done. Just double-clicking the icon of a network node. An a user can flexibly configure the protocol modules attribute dialog box pertaining to this node will pop up A inside a network node. By using this tool, a user can casily user can then set the device's attributes in the dialog box dd, delete, or replace a module with his(her)own module This capability enables a user to easily test the performance of a new protocol 每 Using the node editor, a user can also conveniently set the parameter values used by a specific protocol module. Each box in the node editor represents a protocol module. a user can double-click a protocol module box to pop up its parameter dialog box Regarding how to add a new protocol module to the node editor (i.e, to let it know that a user has added a new protocol module to the simulation engine), readers should refer to the ⊥Cale The protocol Developer Manual for the NCTUns 6.0 Network simulator and emulator o m mammOn A popped-up dialog box of ncTUns 9o package. To let readers quickly get a feel of the operations of /MACBC21VWPHY V30211 PVARPVDVB-S2_FEEDER DVB_=AE this tool, a short tour about running a simple simulation case 60乙1 will be presented in the next chapter Reference [1]SY. Wang and H.T. Kung, A Simple methodology for Constructing Extensible and High-Fidelity TCP/IP Network Simulator. IEEE INFOCOM,99. March 21 0211 5,1999. New York. USA wphy 2 S.Y. Wang and H.T. Kung, "A New Methodology for Easily Constructing Extensible and High-Fidelity TCP/IP Network Simulators, " Computer Networks, Vol 40, Issue 2, October 2002, pp. 257-278 [3]SY. Wang, NCTUns 1.0, " in the column "Software Select。ee Tools for Networking, IEEE Networks, Vol. 17, No 4 ×|n‖F-AA July 2003 The node editor o/NcTUns [4]SY. Wang, C L Chou, C.H. Huang, CC. Hwang, ZM Yang, CC Chiou, and C.C. Lin, The Design and Imple Packet Animation Player mentation of NctUns 1.0 Network Simulator By using the packet animation player, a packet transfer trace Computer Networks, Vol. 42, Issue 2, June 2003, pp 175-19 logged during a simulation can be replayed at a specified speed Both wired and wireless networks are supported. This [5]SY Wang and Y.B. Lin, "NCTUns Network Simulation capability is very useful because it helps a researcher and emulation for wireless resource management visually see and debug the behavior of a network protocol It Wireless Communication and Mobile Computing, is very useful for educational purposes because students can Wiley, Vol. Issue 8, pp. 899-916, December 2005 see how a protocol behaves [6]SY. Wang and K C. Liao, Innovative Network emula tions using the NcTUns Tool, as a book chapter of th " Computer Networking and Networks "book, (ISBN 1 59454-830-7, published by Nova Science Publishers) [7]SY. Wang, C L. Chou, C.C. Lin, "The Design and Imple- mentation of the NCTUns Network Simulation Engine Elsevier Simulation Modelling Practice and Thcory, 15 (2007)57-8 n 0G m an n The packet animation player of NCTUns Summary In this chapter, we have briefly presented the features and capabilities of NcTUns. After reading this chapter, readers now should have a high-level view about NcTUns 6.0. In the next chapter, we will present how to install the ncTUns 2. Getting Started Due to the use of a novel kernel-reentering simulation methodology, NCTUns has two advantages as follows:(1) Any real-life application program can be run on a simulated his chapter presents a simple tour to help readers network to generate traffic and(2) Their performance can be quickly learn how to use NCTUns. First, we give evaluated under different simulated network conditions instructions on how to install NCTUns on a single Thus the real-life application programs pre-installed in this machine. Next, we present step-by-step instructions to illus directory represent only a very small subset ofreal-life appli- trate how to quickly run up a simple simulation case cation programs that can be used with NCTUns During simulation, if a user wants the simulation engine to Installation and Configuration run up an application program that is not pre-installed in this In the following, we assume that when installing the subdirectory (e.g., the P2P BitTorrent program), the user package, the user uses the package's default settings must first copy that program into this subdirectory (i.e /usr/local/nctuns/tools)so that the simulation engine can find a user first downloads the package from the web site at it during simulation. Detailed information on how to specif http://nsL.csIe.nctu.edu.tw/nctuns.htmlStartingfromthe 2.0 version, the operating systems that NCTUns supports is which application programs should be run on which nodes in the gui program is presented in the Topology Ed only Linux and FreeBSD is no longer supported. Right now the Linux distribution supported is Red Hats Fedora 11 which uses linux kernel version 2. 6.28.9 3/usr/local/nctuns/etc After reading the installation explanations and instructions This directory stores the configuration files needed by the (INSTALL, README, FAQ, KNOWN PROBLEM, dispatcher and coordinator programs. Their names are RELEASE NOTE)and running the installation script"dispatcher. cfg, "and"coordinator. cfg, " respectively. Some Install. sh), a directory named"nctuns will be created in the ther configuration files used by NcTUns are also stored /usr/local/ directory, which in turn has several subdirectories here For example, the app. xml, which is read by the gui The name of these subdirectories are"bin""etc """tools. program to explain the usages of pre-installed application BMP",and"lib,"respectively. In the following, we explain programs, is also stored here. An"mdf subdirectory( which cach of these subdirectories brief stands for"module definition file")is created here. Inside this directory, the parameter definitions and dialog box 1 /usr/local/nctuns/bin layout design of supported protocol modules are stored in This directory stores executable programs of the GuI separate subdirectories. The GUI program will read the files program, dispatcher, coordinator, and the simulation engine. inside the mdf directory to know the definition of supported Their names are"nctunsclient, ""dispatcher, "coordinator, protocol modules. The"pscfg" file describes the default and nctunsse, respectively. internal protocol stack used by each supported network 2/usr/local/nctuns/tools 4/usr/local/nctunS/BMP This directory stores executable programs of various appli cations and tools pre-installed by NCTUns. For example, This directory stores the icon bmp files used by the gui currently"stcp,”rtcp:”tp,"" tcpdump."ripe program. These icon files are used for displaying various nctunstcsh,”‘ script,”“stg,”“rtg;”“ tseteny," ifconfig devices' icons and control buttons and"ping"are supported. Some daemon programs used by 5/usr/local/nctuns/ib NCTUns are also stored in this directory For example, the daemon programs used for emulation and Mobile IP are This directory stores the libraries used by the simulation stored here. The agent programs that are used for tactical and engine. For example, the more advanced signal propagation active mobile ad hoc network simulations (e. g "Magentl") model library used by IEEE 802. 11(b) advanced wireless are also stored here. These tactical agent programs can be run physical module is installed here. NCTUns supports on mobile nodes to the moving behavior of mobile RTP/RTCP SDP protocols and implements some of their nodes functions as a library that can be called by RTP/RTCP/SDP application programs Installation procedure Before a user can run up the dispatcher, the coordinator, and Before starting the installation, a user should first carefully the gUI programs, he(she)must first set up the NCTUN read the“ README and“ INSTALL” files. Both of these ShOME environment variable. To do so, a user can type in files contain important installation information. The and execute the "setenV NCTUNSHOME /usr/local/nctuns, RELEASE NOTE file contains notes relevant to cach release shell command in his(her) terminal window (i.e, xterm) if of NCTUns. These notes point out the new functions, bu the csh or tcsh shell is used For the bash shell. the command fixes, performance and GUI improvements, data structure should be export NCTUNSHOMe=/usr/local/nctuns "Two and program changes, etc. between the current and the other environment variables must be set as well. The first is previous releases. The FAQ file answers technical questions NCTUNS TOOLS and the second is NCTUNS BiN. They that may result due to an incorrect installation. The be set to /usr/local/nctuns/tools KNOWN PROBLEM file lists some known system /usr/local/nctuns/bin. respectively problems. For example, if a computer is equipped with a For a user's convenience, the installation script will place the very new video card. the new video card driver may not work nctuns csh and nctuns. bash file in/usr/local/nctuns/etc when well with Fedora 11 the installation is completed. The user can use the command A user then runs the " install. sh"shell script. This script will source /usr/local/nctuns/etc/nctuns csh" to set these install the pre-compiled Linux kernel image patched for environment variables if his (her) shell is csh or tcsh NCTUns. It will also build all executable programs and copy Similarly, if the user uses bash, he (she) can use the them to their default subdirectories in addition it will create command "source /usr/local/nctuns/etc/nctuns bash?"to set 4,096(this number can be easily increased) tunnel special these environment variables files( tunnel interfaces)in/dev. These steps may take some 2. Start up the dispatcher me Now a user can run up the dispatcher, which is located in During the installation, the user should carefully watch out /usr/local/nctuns/bin. Note that the user must be the root user whether some error messages are generated. If any serious to run dispatcher correctly error message is generated, the installation may fail The default port number used by the dispatcher to receive After the installation is successfully finished, the machine messages sent from the coordinator program(s)is, 810.It is must be rebooted and then the user must choose the nctuns 9, 800 for the dispatcher to receive messages sent from the kernel to boot. After the machine boots un with the nctuns GUI program(s). These default settings can be found and kernel. the whole installation can be considered successful changed in the dispatcher. cfg file, which is located in Before start running NcTUns to conduct simulations, the /usr/local/nctuns/etc/ user should carefully read the FINALCHECk file. This file 3 Start up the coordinator lists the important that the performed to run NCTUns correctly. According to our Now the user can run up the coordinator, which is located in technical service experiences, almost every reported /usr/ local/nctuns/bin. Note that the user must be the root user problem is caused by not performing all of these required to run coordinator correctly operations Since the coordinator needs to register itself with the More detailed and up-to-date installation and usage infor dispatcher we must let the coordinator know the port used mation can be found in the nctUns package by the dispatcher to receive the registration messages. (It is 9, 810 in the above example. )This port information is specified and can be changed in the coordinator. cfg file A Quick Tour located in /usr/local/nctuns/etc/ Setting up the environment The second important information that the coordinator must Suppose that a user uses the single-machine mode of know is the ip address used by the dispatcher If the user is NCTUns, before he(she)starts the GUI program, he(she) using the sinyle-machine mode, since the dispatcher and the must perform three operations coordinator are run on the same machine the ip address can be specified as 127.0.0.1, which is the default ip address 1. Set up environment variables assigned to the lo loopback network interface. In case the 127.0.0. 1 IP address cannot work due to some unexpected 8 【实例截图】
【核心代码】