Just Enough Unix

1
Just Enough Unix

• Just enough Unix to enable you to edit, mount and
  view your web-pages on a Unix web-server.

2
Unix Operating System

• Generally operates from a command-line.
• After logging on, met with command-prompt
• miller.cs
• In labs, you will be using X-windows on
  X-terminals.

3
Unix commands

• All unix commands are actually programs.
• You run a program by typing its name at the
  command prompt.
• Generally, the output of a program goes to the
  screen and if the program requires any input, it
  gets it from the keyboard.
• These are called
• stdout stdin

4
File navigation and manipulation

• Unix uses a hierarchical file structure.
• Very similar to Windows and Macintosh.
• Directories not folders.
• Move about with typed commands rather than
  mouse-clicks.

5
ls

• list
• Displays the names of the files in the current
  directory.
• Flags
• -a shows all the files, including hidden ones
• -F puts a / after directories, an after
  executables, and an _at_ after links
• -l displays a long listing of files

6
pwd

• print working directory
• Displays the full path of the current directory
  you are in.

7
cd

• change directory
• Changes the directory to whatever you specify.
• cd name of directory
• Without any directory (just cd) you will be taken
  to your home directory.

8
cp

• copy
• Copies the contents of one file to another.
• cp file to copy new file name

9
mv

• move
• Better name could be the rename command.
• Changes the name of one file to another.
• mv old file name new file name
• Note that the new file name could be a
  directory, which will effectively move the file
  to the new directory keeping the original name.

10
rm

• remove
• Deletes the specified file or files.
• This is destructive!
• They are gone!
• They cannot be retrieved!!!
• rm file name
• Note this does not generally work with
  directories.

11
mkdir

• make directory
• This creates a directory.
• mkdir new directory name

12
rmdir

• remove directory
• This deletes a directory (as opposed to the rm
  command above).
• The directory must be empty otherwise you will
  get an error.

13
Access privileges

• All unix files have privileges associated with
  them.
• These privileges determine who can access the
  file.
• These privileges determine how people can access
  the file.

14
Viewing access privileges

• Use the ls -l command.

drwx------ 2 jimd 8192 Jul 12 1226
nsmail/ -rw-r--r-- 1 jimd 945 Mar 15
1601 old.cshrc -rwxrwxrwx 1 jimd 168
Jan 13 1998 file.exe -rw-rw-rw- 1 nobody
382 Nov 18 1998 old.profile -rw------- 1 jimd
652 Jul 12 1216 old.xsession drwx------
2 jimd 8192 Jun 23 1321
thesis/ -rw-r--r-- 1 jimd 1186776 Jul 13
1507 win32tutorial.ps
15
Types of file access

• Read person can look at the contents of the
  file.
• Write person can change the file.
• Execute person can execute the file (applies
  only to directories and program).

16
Types of users

• User/owner -- the person who owns/created the
  file.
• Group Unix allows for the creation of groups.
• Others/world -- everyone else in the world that
  has access to that computer.

17
To change permissions

• chmod changes the access mode of a file.
• Two methods exist
• symbolic
• absolute

18
chmod - absolute

• Absolute - you specify a numeric equivalent for a
  set of permissions.
• You specify all permissions at once.

19
chmod - absolute

• chmod xxx file
• Where each x is some number from 0 - 7.
• Each number specifies a level of privileges for a
  specific group.

20
chmod - absolute

• e.g.,

chmod 644 index.html
User permission
World permission
Group permission
21
chmod - absolute

• Permissions
• Read 4
• Write 2
• Execute 1
• Set permissions by adding the values of all the
  permissions you wish to set.

22
chmod - examples

• To give yourself read write permission and no
  permission to anyone else
• chmod 600 foobar.txt
• To give yourself read write permission and
  everyone else read permission only
• chmod 644 index.html
• To give yourself full access to a directory, and
  everyone else read execute permission only
• chmod 755 images