SSH

Ssh is logging to another machine from one machine. It is basically starting one process, a shell, in the other. The standard input and standard output from that shell process comes to the client machine. There must be a server in the other machine waiting for incoming ssh request. When a client requests, a connection is established, over TCP. So there must be a port for SSH server. This is secure because it is encrypted. The client can login as any user registered in the server. The user concept we know in GUI environment is not complete. At an operating any number of process can be running, at each process has a user. The user must be registered in the OS, that’s all. SSH is secure. Here private and public keys are used. The users public key is used from the client and private key must be stored in the remote system. The ssh server handles reading and verifying all of this. The key is in the home directory most probably. It can be anywhere as long as the ssh server knows from configuration where to find it. This connection is just sending and receiving text. But the shell that runs on the remote interprets as commands. This is used for mainly communicating with machines that do not have GUI. Server that have no keyboard, mouse or display. Only power and network. How does it work like that. Well you can always access them from local terminals, with network guy connecting connecting a laptop to it and starting a shell there. When the machine turns on, it knows it doesn’t have inputs and outputs. but those are not necessary. All the processes that need to run run, incuding the server. The server only needs the network port. Those are configured from files. There is a harddisk and a filesystem. For those also, a GUI is not needed to manage. You can also mount it in a different machine through a network. Without the SSL (secure socket layer) this is called telnet.