What Is A Shell Account?

Shell

A command line interpreter and a graphical user interface are built into Microsoft Windows and many other operating systems. Unix, Linux, and other Unix-like operating systems do not incorporate the command line interface or the GUI into the operating system. Instead a separate program provides the command line interface.This program is called a shell. A GUI is also provided by a set of programs collectively known as X-Windows.

This separation makes it possible for different users to use different interfaces of their own preference. People who first learned on BSD might prefer to use csh, the shell developed at Berkeley, or tcsh, a superset of the csh command set. People who first learned on AT&T System V Unix systems might prefer the Bourne shell, sh, or the Korn shell, ksh which is a superset of the Bourne shell. People who first learned on Linux, may prefer Bash, the shell used by most Linux distributions. Bash is also a superset of sh, but with a different set of extensions than Ksh.

X-windows

Most modern Unix, Linux, and Unix-like operating systems also include an X-windows based graphical user interface. X-windows is a client-server application that has the advantage of allowing a program running on a remote computer, such as Eskimo North's shell server, to display and accept keyboard input from a different computer, such as your X-windows equipped home computer. Thus, you can sit on your computer at home and run graphical programs that are hosted on another computer half-way around the world transparently. It is even possible to have a windows manager providing a desktop run on a remote computer and display on your home computer. These applications behave no differently than as if they were executing on your own computer.

See: Executing X-Windows Applications On A Remote Host.

Shell Accounts

A shell account provides access to a Unix-like host server computer that is connected to the internet and remains on-line and available for use at anytime from anywhere on the Internet. Eskimo North shell accounts are integrated with e-mail, Usenet News, web hosting, and ftp hosting.

Most shell accounts only allow text access. Eskimo North does allows X-windows graphical access as well as text based shell access. Eskimo North allows remote login to a shell account via rlogin, telnet, or ssh. Of these, ssh is the preferred method in that it encrypts the connection preventing any data from being sniffed between your home computer and Eskimo North's shell server.

A shell account provides a unique user ID. The user ID has a one to eight character login name and a integer UID associated with that login. A shell account includes a home directory which is owned by your user ID. This is used by applications to store user specific configuration information and user specific applications data such as mail folders. In addition you can use it to store personal files, pictures, sound files, video files, applications programs which you will run on the shell server, source code that you compile into an executable application program, shell scripts (files with shell commands), almost anything. You can access files in your directory from anywhere on the Internet.

Shells provide more than a simple command line interpreter. They provide conditional loops, math capabilities, input / output redirection, error handling, variables (some include arrays), importable and exportable environments, automatic execution of initialization commands, pattern matching, command line history, command line completion, and many other program language features. It is possible to write fully functional programs in shell scripts alone and some do exist.

Scheduled Execution

There different methods, at, batch, and cron, are provided for the automatic scheduled execution of programs or shell scripts (files which contain a list of shell commands). The at command allows you to schedule the one-time execution of a program or script at some specified time in the future. The batch command allows you to schedule the execution of a program or shell script as soon as the system load is low enough. The cron command allows you to schedule a program or script periodically.

An example, perhaps you were planning on doing maintenance on a server at 9 PM, you might use 'at' to schedule an automatic shutdown of the server at 8:45. If you were going to rebuild a large software package such as X-windows, you could use batch to schedule the build to start when the system was sufficiently idle. This also would allow the package to be built without being attached to a terminal. It could be done while you are logged off. An example of how you might use cron could be to make scheduled changes to your website, or perhaps automatically forward your e-mail at a particular time and then unforward it later.

Operating System Environments

There are numerous Unix and Unix-like operating systems in use today. Linux, BSD, and System-V derived systems like Solaris are popular. Where the commands differ between these different versions, we have versions of those commands for each flavor in separate directories. If you prefer a BSD environment, put /usr/ucb first in your PATH. If you prefer system V, put /usr/5bin first in your PATH. If you prefer GNU/Linux, put /usr/local/gnu/bin first in your PATH. You probably want to put your own bin directory first so that programs which you compile will take precedence over system programs.

Programming Languages

There are two C compilers present, the C compiler provided with SunOS is 'cc', and the GNU C compiler is 'gcc'. The GNU compiler 'gcc' is the one to use for basically everything unless you have some very archaic C code. The GNU compiler will also compile C+ code. The GNU Fortran compiler (f77) is available.

Perl, Python, and many scripting tools are available. PHP is available on the web server but not presently the shell server.

Website Integration

Every shell account includes web hosting under our domain. There are two special directories you can create and place files in to make them available on web. You can place files in a directory called 'public_html' and they will be visible at http://www.eskimo.com/~username. Where username is the login you chose when you applied for a shell account. Files placed in public_html should be suitable for all ages. Adult material may be placed in adult_html and will be visible at http://adult.eskimo.com/~username.

The purpose of segregating adult content is to allow schools to limit access to adult content while still providing access to material that is acceptable and appropriate for students and also to allow parents who use safe surfing software to make that same distinction. Both hosts are implemented using exactly the same hardware and network infrastructure. There is absolutely no performance advantage to using one over the other.

The integration of your web hosting space with your shell account makes it possible to edit your website on the fly using shell editors such as ex/vi, emacs, or pico. In addition, it also makes it possible to use shell scripts or programs to update your website automatically. These may be scheduled to run periodically with cron.