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UNIX Commands

Getting Started

If you plan to work with cgi scripts or password protection, you'll need to make sure you have the right tools and that your account is set up properly:

  1. Install a Secure Shell (SSH) application on your computer
  2. Request that your account be converted to a shell account

Logging In

You should now be ready to get started. Using your SSH application, log into your account by entering the hostname, username, and password in the application as prompted. For users of the Macintosh OS X Terminal application, enter the following command in the terminal window:

ssh login-name@web.unlv.edu

Upon successful login, you'll be presented with the system prompt, which looks like this:

tarantula %

This is where you'll type your UNIX commands. Many of the basic commands are listed below. For more detailed information on these and other commands, you can also refer to the UNIX man pages by typing man command at the system prompt. For example, to learn more about the ls command, type man ls at the tarantula% prompt as shown here:

tarantula % man ls

UNIX Commands

ls — Get a listing of your files

ls lists the names of the files and subdirectories located in the current directory. The list will look something like this:

picture.gif      index.html      more_stuff
events.html


ls -al — Get a detailed listing of your files

This command lists the files and subdirectories along with additional information. In the example below, notice the "d" in the first position of the third row. The "d" stands for directory, so you now know that this directory contains 3 files and 1 subdirectory. (NOTE: Some info has been deleted for space reasons; deleted info has been replaced with . . . .)

-rw-rw-r-- 1  news_www . . . picture.gif
-rw-rw-r-- 1  news_www . . . index.html
drwxr-xr-x 1 news_www . . . more_stuff
-rw-rw-r-- 1  news_www . . . events.html


pwd — Determine what directory you're in (i.e., the current directory)


cd newdirectory — Change from the current directory to another directory

This command moves you to a different directory. For example, to change from directory /www/html/unlv/mydir to the subdirectory stuff, type:

cd stuff

This will place you in /www/html/unlv/mydir/stuff.


cd .. — Move up one directory level

If you are currently in /www/html/unlv/mydir/stuff, for example, type:

cd ..

This moves you to /www/html/unlv/mydir.


mkdir directoryname — Create a new directory

To create a directory called images, for example, type:

mkdir images


rmdir directoryname — Remove a directory

The directory must be empty. If not, remove any remaining files, then run the command again.


chmod xxx directoryname — Change access permissions on a directory

The chmod (change mode) command lets you change the access permissions of a file or directory. You determine what privileges you wish to grant by setting a numeric figure. The first digit pertains to the owner's privileges (that's you), the second pertains to the group's privileges (users who are members of the same group), and the third pertains to the world's privileges (i.e., the people viewing your webpages). Each digit is determined by the addition of three components:

read = 4
write = 2
execute = 1

Suppose I have a directory that I don't want anyone but myself to be able to access. By default, the web server sets file permissions to 755 (read/write/execute for the owner and read/execute for the group and world). To make the directory accessible to only myself, I would issue the following command:

chmod 700 directoryname

This gives me full privileges as the owner (4+2+1) and no privileges to anyone else (0).

TIP: Set the execute bit when you have a directory or an executable file (cgi script). Also, never give write permission to the world unless you don't mind other people tampering with your files.

For more details, refer to the man pages.


clear — Clear the screen

Clears the screen and moves the tarantula % prompt to the top of the screen.


exit — Logout

Logs you out when you're through with your session.


cp file1.html file2.html — Copy a file

For example, to copy the file events.html to schedule.html, type:

cp events.html schedule.html


rm filename.html — Remove (delete) a file

Use this command carefully. Once deleted, your file is gone forever!


chmod xxx filename.html — Change access permissions on a file

The chmod (change mode) command lets you change the access permissions of a file or directory. You determine what privileges you wish to grant by setting a numeric figure. The first digit pertains to the owner's privileges (that's you), the second pertains to the group's privileges (users who are members of the same group), and the third pertains to the world's privileges (i.e., the people viewing your webpages). Each digit is determined by the addition of three components:

read=4
write=2
execute=1

Suppose I have a cgi script that I need to make executable. By default, the web server sets file permissions to 644 (read/write for the owner and read only for the group and the world). That means that the server won't execute my script until I change the permissions. I want to have read, write, and execute privileges for myself (4+2+1) as the owner, but want to limit everyone else to read and execute (4+1).

IMPORTANT: Never give write permission to the world or you'll be putting your files at risk.

Here's the command I would issue to make the file executable:

chmod 755 myscript.pl

For more details, refer to the man pages.


mv oldfile.html newfile.html — Rename a file

Use this command to rename a file or to move a file to another directory.