Basic UNIX Commands

Content

· Unix account

Unix account

The main server for graduate students and research is flame. This is a multi-user UNIX server that can be used for doing assignments, checking email, and hosting a web page. Every student who takes a computer science class automatically receives a Unix account. If you are a graduate student, you will receive an account on flame.cs.dal.ca. You may also login the undergraduate server torch (torch.cs.dal.ca) using the same username. The initial password is the user's student ID (Banner) number. (Don't forget that Unix system is case sensitive, so “B” is not same as “b” in this system)

All users with a Unix Account are also entitled to a Windows Account. Windows accounts are administered by the Novell file server called Skywalker (csskywalker.cs.dal.ca). New Novell accounts have the same username as their corresponding Unix account. The initial password is the user's student ID (Banner) number.

Now you can use your username and password to login graduate computers.

Logging in server

You can log in to flame.cs.dal.ca by either sitting at a Sun workstation or by using an ssh program such as putty to log into torch.cs.dal.ca.

When using a Sun workstation:

1. Type your username to the system login prompt.

2. Type your password to the system password prompt.

When using putty:

1. Login a Windows computer with your Windows account username and password.

2. Start up Putty, which is a program installed on all Windows computers in the Computer Science building.

3. Enter the host name of the server in the Host Name field. eg. flame.cs.dal.ca

4. Click on the SSH radio button

5. Click the Open button. If this is the first time you connect to this server you will be asked to store the server's key fingerprint. Click yes to save the key and continue.

Note: If the connection has been listed in the session list, it means that this configuration has already been saved. Then you can skip step 3~5, select the connection name from the session list directly and click the Load button. Then click the Open button to establish the connection.

6. Type your username to the login prompt.

7. Type your password to the system password prompt.

Directory Operations

Notes: there are several special directories in Unix, such as . / .. / ~. In Unix, . means the current directory, .. means the parent of the current directory, while ~ means your home directory (When you first login, your current working directory is your home directory).

Ø Listing files and directories

Command Description: list the contents of your current working directory

Ø Create a new directory

mkdir newdirectory

Command Description: make a new subdirectory in your current directory. For example, when you type:

mkdir dir1 A new subdirectory called “dir1” is createdin your current working directory.

Ø Change to specified directory

cd directory

Command Description: change the current working directory to ‘directory’. The specified directory path ‘directory’ must exist. For example, when you type:

cd dir1 the directory “dir1” will become your current directory.

and

cd .. will take you one directory up the directory hierarchy.

Ø Copy directory

copy –r directory1 directory2

Command Description: copy the directory1 and its contents to directory2. The directory1 will be a subdirectory of directory2 after this operation.

Ø Remove a empty directory

rmdir directoryname

Command Description: remove the directory. This directory must be empty first, that is, no file exists in this directory.

Ø Remove a non-empty directory

rm –r directoryname

Command Description: remove the directory as well as all its contents.

Ø Show current directory pathname

pwd

Command Description: lists your current location with respect to your root directory

File operations

Ø copy file to another filename

cp sourcefile targetfile

Command Description: Copy the source file to a new file (target file). The source file must be a current file, and the target file might be a new file name or current file for over- writing. Both source and target can include directory paths.

Ø move file to directory/rename file

mv sourcefile newfilename

Command Description: rename the source file by giving it a new file name.

mv sourcefile directoryname

Command Description: move the source file from original place to another directory. This command has the effect of moving rather than copying the file, so you end up with only one file rather than two.

Ø remove /delete file

rm filename

Command Description: remove/delete the file. The file name can include a directory path.

Ø Display file content

cat filename

Command Description: display the contents of the file on the screen. If the contents of the file are longer than the size of the window, they will scroll past screen so that part of them may be unreadable.

less filename

Command Description: display the contents of a file on the screen one page at a time. Press “space” on keyboard if you want to see another page, type “q” if you want to quit reading.

Other useful commands

Ø Change access permission

chmod n1n2n3 filename/directoryname

Command Description: change the permissions of the file/directory (only the owner of this file/directory can use this command to change its access permissions.

Where n1, n2, n3 are numbers ranging from 0 to 7:

n1 is a number that represents access permissions for the owner

n2 is a number that represents permissions for the group, where group is defined by the host administrator (e.g. all students, all grad students etc.)

n3 is a number that represents permissions for the others.

n1, n2, and n3 can be calculated as follows:

Each file/directory has three types of access properties:

· r, indicates read permission. For a file, it means the permission to read and copy the file. For a directory, it means the permission to list files in this directory

· w, indicates write permission. For a file, it means the permission to change a file. For a directory, it means the permission to delete files from this directory or move files into it

· x, indicates execution permission. For a file, it means the permission to execute a file. For a directory, it means the right to access files in the directory (you can read files in the directory provided you have read permission on the individual files).

Thus for a file/directory, each field (owner, group, others) may have a total of three properties associated with this field and each property has a numerical value:

· Read (4)

· Write (2)

· Execute (1)

For example, if you want to give yourself Read, Write and Execution permission to a file, called 'sample.txt', give the group members Read, and Execution permission, but deny any access to others. Here n1, n2, n3 can be calculated as:

n1 is calculated for owner: Read(4) + Write (2) + Execute(1) = 7;

n2 is calculated for group members: Read(4) + Execute(1) = 5;

n3 should be zero since you do not give any permission of this file to others;

So we type

chmod 750 sample.txt to change the access permission of this file.

Ø Editing

There are several text editors like vi, pico, emacs. Here we use pico as an example.

pico filename

Command Description: start pico vi to edit the text file. If no filename is provided, the command will start pico with a new file.

Commands for this editor are across the bottom of the window. The "^" indicates the "ctrl" key on keyboard. For example: the command ‘^X’ implies pressing "ctrl" and the character ‘X’ at the same time. Here are detail descriptions of some useful commands in pico:

· ^G display the help text.

· ^R insert external file at the cursor position.

· ^O write buffer to a file and save it. If no filename is provided when pico starts, a prompt will appear on screen. Type the filename under the prompt.

· ^X quit pico and save buffer.

· ^W search string in the text.

· ^ ^ mark the current cursor position as the beginning of selected text.

· ^K cut the selected text (from the marked beginning of the text to the current cursor position.)

· ^U paste the cut text to the current cursor position.

· ^V move forward a page of the text.

· ^Y move backward a page of the text.

· ^A move to the beginning of the current line.

· ^E move to the end of the current line.

Ø Get online help

Man command

Command Description: get on-line manual of this command. The manual pages tell you which options a particular command can take, and how each option modifies the behaviour of the command.

whatis command

Command Description: gives a one-line description of the command, but omits any information about options etc

You can find more Unix commands here

last revised: July 2004