Macon User Group Linux SIG

1
Macon User Group Linux SIG

• What is the Command Line?
• (and why should I care?)?

2
The Command Line

• A text-based mode of operating where commands are
  entered at a prompt.
• A command line can be accessed from within a
  graphical environment as well as from virtual
  consoles.
• Console is synonymous with terminal.
• Ubuntu has six virtual consoles, enabling the
  screen to be used for six independent work
  sessions.

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What Can You Do?

• Perform routine tasks
• Log in/out
• Change passwords
• Etc.
• Implement basic file management
• Execute basic system management

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User-based Security 1

• Ubuntu grants superuser privileges to the first
  account that is set up.
• The superuser can modify the system, and make
  changes to any other user's account.
• To use superuser privileges, enter sudo then
  the command.
• The password must be entered every time. (There
  are ways to avoid this.)?
• Other users can modify only their own accounts,
  and not the system.

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User-based Security 2

• sudo is not the same as root.
• In Ubuntu, the root account is disabled by
  default, in preference to sudo.
• If you want to get to a root shell (thereby
  removing the need to type sudo and the password
  every time) just enter sudo -i to get the root
  prompt (). To return to a normal prompt, type
  exit and press return. This does not create a
  root account, however.

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What is a Command?

• A command is an instruction to Linux to perform
  some operation.
• Commands consist of one or more elements. The
  first element is always the actual com-mand,
  followed by parameters or options.
• Options are prefixed with hyphens.
• An important option is the --help option (with 2
  hyphens)?
• Using this option displays all the options
  available for the command.

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Important Commands in Linux

• Most Linux commands are fairly mnemonic.
• ls -- (list) shows the files in the current
  directory
• Option -a (all) displays hidden files
• Option -l (long) displays detailed description
• Options can be combined ls -al
• man -- displays the manual page for a command.
• A detailed manual is available for all commands.
• pwd -- returns name of present working directory

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Getting to the Command Line

• Go to Applications Accessories Terminal
• Or, press Ctrl-Alt-F1
• This gets you to one of the 6 virtual consoles
• Use Alt-F1 thru Alt-F6 to cycle through Alt-left
  or -right cursor key does the same
• Alt-F7 gets you back to Gnome

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The Shell 1

• A console in Ubuntu normally runs Bash the
  Bourne again shell, the most widely used
  derivative of the Bourne shell.
• When you have opened the shell, you will be asked
  to log in, using your user name and the password
  supplied when the account was created.
• The Ubuntu shell prompt is user_at_host
• The tilde () indicates your home directory

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The Shell 2

• If you are root, the prompt changes from
  to .
• The appearance of the prompt is governed by the
  environment variable PS1.
• To see the contents of PS1, enter echo PS1
• Use the export command to change PS1 temporarily
  export PS1/u will show only the username
  and the prompt.
• Some values for options are shown in the handout.
• Also see http//www.tidp.org/HOWTO/Bash-Prompt-HOW
  TO

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File Navigation 1

• Navigating through the file system
• cd changes directories
• cd /etc/apt moves you straight to that
  directory
• cd .. moves up one level (note space before ..
  )?
• cd takes you to your home directory from
  anywhere
• So does cd
• pwd tells you where you are in the file system
• ls lists the contents of the current directory

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File Navigation 2

• More on ls
• There are many options for use with this command
• ls -a lists all files and directories in the
  current directory
• ls -l shows permissions, sizes, groups, etc.
• ls -al combines those options
• ls -R scans and lists contents of all
  subdirectories. This may get long, so put the
  result into a text file with ls -R listing.txt.

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File Management 1

• Basic file management with the shell involves
  only a few easily remembered commands
• cat filename outputs contents of filename to the
  display.
• mv file1 file2 renames file1 as file2
• mv file dir moves file to specified directory
• cp file1 file2 creates file2 as copy of file1
• rm file deletes the file
• rmdir dir deletes dir (if it is empty)?

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System Management 1

• Permissions
• Under Linux (like Unix) everything in the file
  system, including directories and devices, is a
  file.
• Every file on your system has an accompanying set
  of permissions based on ownership.
• Permissions are the basis for security under
  Linux they designate a file's read, write, and
  execute permissions for you, members of your
  group, and others who may have access to the
  system.

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System Management 2

• Do a long-format listing of some files
• drwxr-xr-x 2 root root 4096 2008-09-23 1657 .
• The first 10 characters are the permissions on
  this file
• d indicates that this file is a directory
• The next 3 are permissions for the owner rwx --
  read, write, and execute.
• Characters 5 thru 7 are for group members, and 8
  thru 10 are for others. Note that both are r-x,
  where the hyphen indicates that these accounts do
  not have write capability in this directory.
• The '2' indicates that there are 2 links to this
  file.

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System Management 3

• Continuing with this listing
• drwxr-xr-x 2 root root 4096 2008-09-23 1657
• 'root' is the owner, in the group named 'root'
• 4096 is the size of the file in bytes
• Then the date and time of creation is shown.
• The chmod command allows changing the
  permissions only root and the owner can do this

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System Management 4

• Parameters to the chmod command are
• Categories concerned u (user), g (group) and o
  (others)?
• Characters for modification - (delete), (set),
  and (insert)?
• The abbreviations r (read), w (write), and x
  (execute)?
• Names of files to be modified, separated by
  spaces
• To give write permission for 'others' on the file
  'foo', chmod ow foo
• Other related commands are chown and chgrp, which
  let the owner (or root) assign files to other
  owners or groups.