The Distributed Shell And Remote Execution Facilities

With the development of the technology of hardware, software and high-performance computer network, the interest of humans for distributed computing system is rising. From the time that programmers have to make an appointment before using computers to the time of the time-sharing system, the development of operating systems is rapid. However, in the share environment based on network, users encounter new troubles of using and managing the time-sharing system. The operating system software of individual computers should permit to copy files and telnet among these computers in the network and users have to know the differences between local and remote objects and their positions. If the scale of the network is large, the problem will become complex. Although people find some ways to solve it, no one is satisfied like the share environment of time-sharing systems. In fact, the primary reason is that traditional systems are not designed for the multiprocessors and multi-file systems circumstances; in this situation, distributed computing systems are necessary. Distributed Computing System is the cluster of several single computers units connected with each other by local area networks, acting as integration In the sight of users, the system is just like a single computer, say, they don't need to know how many machines there are, where they actually are, what functions they perform separately, where the file system locates, which machine task works on, and any other detail information about the configuration of the system. The shell in this paper is one part of our distributed operating system. In general, the formats of remote shell commands existing in UNIX, such as rsh, rcp, rlogin and rexe, etc are the forms of command lines, the compounding of obvious command and parameters. When using these orders, users have to designate machine name of executing commands, input user name and password of the machine and consider some other problems, for example, whether needful files for performing remote commands are on remote machine. Although we must admit that these measures have their own using environment, it is certain that the environment is not distributed computing system, because the feature of the system-transparency request that in the sight of users, the system is just like a single computer, users don't need to know where data are and where processes are executed. Therefore, the realization of the shell requires us to change another manner. In technology: 1)Daemon. Daemon is a kind of long-life process. When system is booted, it is started, when system is shut, it is closed. Because daemon can not control terminal, it is run on background. 2) Network File System. NFS is exploited and researched by Sun. The essential idea is that each file service administrator provide its file system with a standard view, in other words, no matter how local file system realizes, each NFS service administrator supports a identical model that actualizes by a communication protocol that admits clients to access file servers with identical means. 3) Pseudo terminal. In realization: First of all, the non-preemptive process, one of methods of process transfer, is utilized in the design, choosing one node and starting the process on it. Secondly, three daemons are installed on each node, including the daemon of broadcasted broadcasting messages with CPU idle rate ,the daemon of clid receiving messages with CPU idle rate from nodes in distributed computing system and sorting them in descent, remshd daemon executing the commands from remote node. Thirdly, through modifying the source code of bash the shell will pick...