Berkeley r-commands facts for kids

The Berkeley r-commands are a group of computer programs. They were made to help users on one Unix computer connect to another. You could use them to log in or send commands over a computer network. These commands were created in 1982 by a team at the University of California, Berkeley. They were based on an early version of the TCP/IP system, which is what the Internet uses.

The Berkeley team added these r-commands to their own Unix operating system. This system was called the Berkeley Software Distribution (BSD). The r-commands first appeared in BSD version 4.1. Some of these programs include: rcp (for copying files remotely), rexec (for running programs remotely), rlogin (for logging in remotely), and rsh (for using a remote command line). Other commands were rstat, ruptime, and rwho.

The r-commands were a big step forward in how computers connected. They became a common way for Unix systems to work together. However, as more people used the Internet, problems with their security became clear. Starting in 1995, new and safer ways to connect, like Secure Shell (SSH), began to replace the r-commands.

What are r-commands?

The r-commands are a set of tools that let you work with other computers over a network. They were designed for Unix-like systems. Each command starts with "r" for "remote." This means they help you do things on a computer that isn't right in front of you.

rlogin: Logging in Remotely

rlogin lets you log into another computer far away. It's like sitting at that computer, but you're using your own. This command uses a special network connection called TCP port 513. It communicates with a program called rlogind on the other computer. rlogin is similar to the Telnet command. However, it works best with Unix-like computers.

rsh: Running Commands Remotely

rsh stands for "remote shell." A shell is like a text-based window where you type commands. This command lets you run commands on another computer without fully logging in. You can send commands and see the results on your own screen. rsh uses TCP port 514 for its main communication.

rexec: Executing Commands with a Password

Like rsh, rexec lets you run commands on a distant computer. The main difference is that rexec requires a username and password. This makes it seem more secure. However, it sends your password without any protection. This means others could easily see it. rexec uses TCP port 512.

rcp: Copying Files Remotely

rcp means "remote copy." This command helps you copy files or folders. You can copy from your computer to a remote one. You can also copy from a remote computer to yours. Or even from one remote computer to another. It works like the regular copy command. But you add the remote computer's name to the file path. For example: `rcp my_file.txt remote_computer:~/documents/my_file.txt` Be careful, because rcp will overwrite files with the same name. It won't ask you for permission first. rcp uses TCP port 514, just like rsh.

rwho: Seeing Who is Online

The who command shows you who is logged into your current computer. rwho takes this a step further. It lists all the users logged into other Unix computers on your local network. A program called rwhod helps rwho do this. It keeps a list of what's happening on the network.

rstat: Checking Computer Performance

rstat is a command that gets information about how well a computer is working. It collects performance details from the computer's core system.

ruptime: Checking Computer Uptime

The uptime command tells you how long your computer has been running. ruptime asks all computers on the local network for their uptime. It then shows you a report. If a computer doesn't respond, ruptime will say it is "down." This information is also gathered by the rwhod program.

Why r-commands are not used much anymore

The r-commands that needed you to log in, like rcp, rexec, rlogin, and rsh, had some big security problems. Because of these issues, they are not used very often today. Many Unix and Linux systems no longer include them by default.

Here are some of the main security risks:

• Passwords were not secret: All information, including your passwords, was sent without any encryption. This means anyone watching the network could easily see your password.
• .rhosts files were risky: These files were meant to let you log in without a password. But they relied on trusting the other computer's name or address. This made them easy for bad people to trick. Many computer experts now forbid using these files.
• Easy to trick the system: The r-commands partly trusted the other computer to be honest. A bad program could pretend to be a trusted computer. It could then gain access without permission.
• Network sharing made it worse: If user folders were shared across the network, it made the r-commands even more vulnerable. If one part of the system was unsafe, it could affect the r-commands too.

Because of these problems, safer tools like SSH have replaced the r-commands. SSH encrypts all information, making it much harder for others to snoop.

See also

In Spanish: Rlogin para niños

• List of Unix commands