CLI Spells for the Raspberry Pi

Revision as of 06:48, 16 May 2012 by Brian (talk | contribs) (Task $ sudo. Invoking commands as an admin user)
Jump to: navigation, search

This Page is a Quickstart for Command Line Interface on the Raspberry PI.--Brian 09:13, 20 April 2012 (UTC) Back to Beginners Page

Why Do I Need the CLI?

(CLI-Command Line Interface)

The Raspberry Pi operating systems that you can download for your SD card are all versions of Linux. A graphical user interface (GUI) for Linux is provided by the X Windowing System, together with a window manager. There are lots of different window managers, for example the one being used at time of writing with the Debian "squeeze" OS is LXDE. For some OS distributions, the windowing system is started up automatically when the machine starts up, but if not then you are in the Command Line Interface, which allows you to type commands and get information back. Most of us will immediately type "startx" to bring up the GUI, but even when you are using the GUI you can still get a CLI in the form of a terminal window. You can bring this up from the start menu; usually it is called something like X Terminal.

You need the CLI because there are many things things that either can't be be done using GUIs, or are much easier using the CLI. In addition there are situations when you would rather not run the X Windowing system, because it takes up a lot of processor power and memory. Also a Raspberry Pi doing some task or other may well have no screen at all, and you may manage it remotely using a remote log in to a terminal.

Windows and Mac users are generally guided away from the CLI hence this Quick start Guide.

The quick answer to "why do I need the CLI?" then, is that the CLI is going to be a very useful tool for Raspberry Pi users.

Commands are just programs

When you type a into the terminal you are running programs. Most of the commands listed here run programs that give you the ability to command the system to do something. When you add programs to your pi, you will be able to run more commands. This means that if a command you run and expect to work returns the message $ bash: foo: command not found...

It just means that you have not installed "foo" yet. Most of the commands described i this page are the kind of house keeping commands that come with bash. Each program has an original author who is acknowledged at the bottom of the man page.

To use the CLI you need to know commands and the default command set is contained in the "shell" you are using. There are Lots of shells out there and the one on this Raspberry Pi is Bash Wikipedia Bash Entry.

To find the syntax for a command do an Internet search for the command or find a Bash Quick Reference Card. In this wiki entry, each command has a link to the Wikipedia entry for that command.

If you want to know how to use commands without using the Internet then use man (short for manual).

$ man <command> or $ info <command>

from the CLI to be sent to a page of guidance.

The guidance given by "man" is sometimes a bit formal to the point that it could be said, "if you think you know a command then go to the command's man page in order to find out that you don't really".

General Syntax of Commands

Commands take the form

<Command> | -<Switches> | <Parameters> | <Target>

<> are often used in Syntax guides to indicate that the <> surround a place for a command rather than an actual command. | is used to denote OR or Optional so in the line above we read that a Command can be used on its own but may be followed by Switches (single letters, preceded by a hyphen that adjust what the command does), Parameters (Things that the command needs to know in order to work) and a Target (The thing that the command will be applied to).

e.g. "ls -l /home/brian" means List in Long Format (the -l switch) the directory (target) /home/brian

mount -F smbfs //workgroup;fred:foo@ /mnt/net

Means use the username fred and password foo (parameters) to make the shared drive called homes on the Windows server at (parameter) appear in the directory tree at the point /mnt/net (target) using the Server Message Block Filing System (the -F switch)

Task $ cd. Navigating the file system using "cd"

The file system in Linux is Hierarchical with nested directories. (Often called Folders) in a "Tree". The top of the directory structure is "/" and Directories underneath / are referred to using "Paths" just like urls in a web browser. To go to a particular place in the directory structure you use cd. e.g. cd / will take you to the top of the Directory Tree

To go to a particular place use cd followed by the location in the tree.

cd /home/brian/Documents will take you to "Brian's" home directory Documents Folder. File & Directory Names are Case Sensitive in Linux

To go one Directory "Up" the tree then do "cd .."

Task $ ls. Listing the files and Folders in a particular place

$ ls list all the file in the current directory. $ ls -l list all the file in the current directory and display the long version of the information about each file or directory. The output may be colour coded depending on the terminal preferences that you have set. ls -l tells you (amonst other stuff) the size, owner and security setting on each file. Other useful invocations are ls -R Recursive. i.e. list contents of sub-directories as well as this directory. ls -A Show "Hidden" Files. ie. Hidden files are file names that start with a dot which in Unix GUI file navigators are (by default) hidden.


$ ls

An_Gott_und_meine_Mutter.mid Domestic Programming Test.mid

An_Gott_und_meine_Mutter.mscz Engineering Quantum Physics Tutoring

appliances FluidR3_GM.ins School Windaz


$ ls -l

total 336

-rw-rw-r--. 1 brian brian 2429 Apr 2 20:27 An_Gott_und_meine_Mutter.mid

-rw-rw-r--. 1 brian brian 4085 Apr 2 19:52 An_Gott_und_meine_Mutter.mscz

drwxrwxr-x. 4 brian brian 4096 Apr 2 20:38 appliances

-rw-rw-r--. 1 brian brian 10919 Apr 2 19:52 brotplot.odt


Task $ chown Change Ownership of directories and files

In the Long List above, the files are owned by Brian and are also in the Brian Group. $ chown fred brotplot.odt will result in this result in ls -l

-rw-rw-r--. 1 fred brian 10919 Apr 2 19:52 brotplot.odt

The file is still in group brian but is owned by fred

$chown foo:foo brotplot.odt will result in

-rw-rw-r--. 1 foo foo 10919 Apr 2 19:52 brotplot.odt

The group has change also. See Also chgrp

Task $ chmod Change Access to directories and files

When long list files, the left hand column takes the form xuuugggwww. x is a letter describing what kind of thing the list entry is and can be various things but most commonly is d, l or -. d stands for directory, l for link - for a file.

The uuugggwww describe access rights for the owner (user), group and the world. (i.e. everyone not in the set owner or group). In each triplet, the order is rwx, read for ability to read, w for ability to write and x for ability to execute. If the x flag is not set then the file will not run as a program.

This line from above tells us that fred and the group called students both have read and write access where everyone else has read access only.

-rw-rw-r--. 1 fred students 10919 Apr 2 19:52 brotplot.odt

There are various ways of chmod use but probably the easiest is to consider the groups u for user-owner, g for group, o for other(everyone else) and a for all three.

Use chmod as follows

chmod o+w brotplot.odt means add write access for the other group to brotplot.odt
chmod a-r brotplot.odt means remove read access for the all three (user, group and other) from brotplot.odt
chmod u+x brotplot.odt means add execute access for the user/owner to brotplot.odt

Task $ sudo. Invoking commands as an admin user

This command introduces the SuperUser or root user. Many commands are only permissible to the root user and by invoking sudo before a command, you are saying "do the following command as the root user". When you do this, you will be asked for your password and if you have system permissions (commonly called being in the admin group) to be a root user then the command will be run. If you do not then a message will tell you so.

root is the name for the main administrator of a Unix like system. The default Debian distribution has no root passwd set and you do privileged commands by prepending the command with "sudo".

Example adduser brian adduser: Only root may add a user or group to the system.

sudo adduser brian

  1. You now enter a sript that sets up a new user called brian

Anytime you get an "Only root can ...." message, try the sudo command.

There is another way of doing things as root user and that is by using

Task $ su - Becoming the admin user

which stands for "substitute user" (or SuperUser) & as invoked here means "become the root user". From this point on, all command run as the super user. Invoking this command will cause you to be asked for the root password. Some systems do not allow this to happoen in a default install in which case you have to enable the root user. When you enter passwords in Unix like systems, you will not see asterisks or anything at the prompt but the password is being entered nevertheless. If you habitually do everything as the root user, eventually you will do something both educational and disasterous. For example, you could invoke

"rm -r -f /* " and delete all the files in the whole system.

$ rm -r -f ./* would just delete the files in the current directory. You do not usually get warnings as root user. (Other than this one).

Task $ touch. Create a new empty file

Go to where you want the file to be and invoke

$ touch <filename>

Task $ mkdir. Create a new empty directory

Go to where you want the directory to be and invoke

$ mkdir <Directory Name>

Task $ rm. Remove a file

Go to where you want the directory to be and invoke

$ rm filename

Task $ rm. Remove a Directory

Go to where you want the directory to be removed

$ rm -r -f <Directory Name>

This will remove the directory, all its contents and also any sub directories and their contents.

Task $ mount Connect to a device or Filing System

Mount is the way in which you connect a Unix system to external devices. There is no "C" drive as in Windows. What happens in Linux (& FreeBSD/OSx) is that a device is mounted in the filing system somewhere and when you navigate to that place. The items offered by the device will appear at that point.

This is a complex command. The switches, parameters and target of the Mount command will vary according to the protocol of the system being mounted. Some things will automount. This is why, when you plug a SDcard into a modern Linux, the filing system will automatically pick it up.

Manual Mounting requires a "Mount Point". That means a directory which will be filled with the mounted device when it is mounted. Often, this is in the directory /mnt/ somewhere.

Generally, first ensure there is a mount point, if not then create a directory at the point needed. e.g. $ mkdir /mnt/netfolder

The issue Mount with the necessary switches, parameters and directories.

e.g. From above.

mount -F smbfs //workgroup;fred:foo@ /mnt/net