Operating Systems and Using Linux

1
Operating Systems and Using Linux

• Topics
• What is an Operating System?
• Linux Overview
• Frequently Used Linux Commands
• Reading
• None.

2
What is an Operating System (OS)?

• A computer program
• Performs many operations, such as
• Allows you to communicate with the computer
  (tell it what to do)
• Controls access (login) to the computer
• Keeps track of all processes currently running
• At this point, your main concern is how to
  communicate with the computer using the OS

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What Is A Process?

• A process is a task or program that you have
  requested the operating system do on your behalf.
• That process is given an identifying number,
  called a PID (process ID).

4
How Do I Communicate With the Computer Using the
OS?

• You communicate using the operating systems
  user interface.
• Graphical User Interface (GUI) Microsoft
  Windows, Linux KDE
• Command-driven interface - DOS, UNIX, Linux,
  Microsoft Command Prompt
• We will be using the Linux operating system,
  which is very similar to UNIX.

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How Do I Communicate With the Computer Using the
OS? (cont)

• When you log in to the Linux system here, a user
• prompt will be displayed
• linux1 _
• where is the number of the Linux server that
  you have connected to. You may use any of the
  Linux servers.
• The number in the brackets will change as you
  work. It is
• the number of the command that you are about
  to type.
• If this prompt is not on the screen at any time,
  you are not
• communicating with the OS.

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User Prompt

• While the normal (or default) prompt is
  linux1you can change this.
• To learn Linux well enough to do this, we
  recommend that you take CMSC121, a one credit
  course.

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Linux Overview

• Files and Filenames
• Directories and Subdirectories
• Frequently Used Commands

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Files

• A file is a sequence of bytes.
• It can be created by
• a text editor (xemacs or pico)
• a computer program (such as a C program)
• It may contain a program, data, a document, or
  other information .
• Files that contain other files are called
  directories (sometimes called folders).

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Linux Filenames

• Restrictions
• May not contain blanks or other reserved
  characters.
• Have a maximum length (however, make your
  filenames long enough to be useful and short
  enough to type without making a mistake.
• Are case sensitive.
• It is best to stick with filenames that contain
  letters (uppercase or lowercase), numbers, and
  the underscore ( _ ) for now.
• Filenames that start with a period are hidden
  files, so that when see the files in a directory,
  they dont show up.

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Directories

• Directories contain files or other directories
  called subdirectories. They may also be empty.
• Directories are organized in a hierarchical
  fashion, or directories can contain other
  directories.
• They help us to keep our files organized.

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Directories (cont)

• /afs/umbc.edu/users/j/d/jdoe28
• junk recipes notes
• pies cookies CMSC104
• apple peach choc_chip

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Directories (cont)

• One example is to have a directory for CMSC104.
• Inside you could have a directory for each
  project, and whatever.
• Rule of Thumb Never have more files in one
  directory than fits on the screen when you list
  them.

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Directories (cont)

• Your home directory is where you are located when
  you log in (e.g., /afs/umbc.edu/users/j/d/jdoe28).
  
• The current directory is where you are located at
  any time while you are using the system.
• Files within the same directory must be given
  unique names.
• Paths allow us to give the same name to different
  files located in different directories.
• Each running program has a current directory and
  all filenames are implicitly assumed to start
  with the name of that directory unless they begin
  with a slash.

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Subdirectories

• Are used for organizing your files
• For example,
• make a subdirectory for CMSC104
• make subdirectories for each project
• CMSC104
• project1 project2 . . .
  project8

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Moving in the Directory Tree

• . (dot) is the current directory.
• . . (dot-dot) is the parent directory.
• Use the Linux command cd to change directories.
• Use dot-dot to move up the tree.
• Use the directory name to move down.
• Use the complete directory name (path name) to
  move anywhere.

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Pathnames

• Pathnames that start at the beginning (and start
  with a /) /afs/umbc.edu/users/j/d/jdoe28are
  called absolute pathnames.
• Pathnames can be shorted, so that if jdoe28 is
  the current directory and we have a file in that
  directory call schedule, we can edit it with just
  the filename (a relative pathname)pico schedule

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Permissions

• Files and directories have permissions.
• There are three sets of permissions for three
  groups
• Read, write, execute (or, if a directory, access)
• User, group, other
• You are the user, and can set and change
  permissions.

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Frequently Used Linux Commands

• passwd, man, lpr
• pwd, ls, cat, more, cd, cp, mv, rm
• mkdir, rmdir
• ctrl-c, ctrl-z
• References
• Linux man pages
• Links from the 104 homepage
• Books and the Internet

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Linux Command Format

• Fromat cmd options arguments
• Options and arguments are optional.
• Options start with - or - -
• Options are different for each command.
• Arguments are different for each command.
• When in doubt, look up the command in the on-line
  help, man.

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man

• On-line help.
• Argument is the command you wish to have help
  for.
• Option k is most common, which looks for a
  description that contains the argument.
• When the description of a command takes more than
  one screen to display, press the space bar for
  more information and q to quit.

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man (contd)

• Exampleburt_at_linux1 man -k passwd
• htpasswd htpasswd (1) - Create and
  update user authentication fileskpasswd
  kpasswd (1) - change a user's Kerberos
  password
• mkpasswd mkpasswd (1) - generate
  new password, optionally apply it to a user
• passwd.nntp passwd.nntp (5) - passwords
  for connecting to remote NNTP servers
• saslpasswd saslpasswd (8) - set a
  user's sasl passwordsaslpasswd2 saslpasswd2
  (8) - set a user's sasl password
• v5passwd v5passwd (1) - change a
  user's Kerberos password

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passwd

• Used to change your password.NAME passwd -
  update a user's authentication tokens(s)
• SYNOPSIS
• passwd -k -l -u -f -d -n mindays
  -x maxdays -w warndays -i inactivedays -S
  username

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lpr

• Used to print something on the printer.
• You must pay per page.
• Pick up your print-out at ECS-019.

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cd

• Change directory.
• With no argument, it will take you back to your
  home directory.
• With a argument, it will set that directory to be
  your current working directory, assuming you have
  permission to access the directory.

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pwd

• Print the current working directory.
• Helpful when you forget where you are.
• Has no options or arguments.

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ls

• Lists the names of files in a directory.
• Arguments are name(s) of file(s) and/or
  director(ies).
• Normally, when you specify a directory, you get
  the contents of the directory.

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ls Options

• -a all (including hidden files)
• -d just show the directory, not the files in the
  directory
• -F classify files as ordinary, directory (/), or
  executable ()
• --color classify with color
• -l long format
• -r show in reverse order
• -R recursive, show the contents of all
  subdirectories.

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cat

• Used to display the contents of a file.
• If there is too much to fit on the screen, the
  first part scrolls off and leaves only the last
  screenful.
• Argument is the name of a file or files.
• Useful option is n (or number) to show the line
  numbers.

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more

• More shows a screen full of a file at a time.
• SYNOPSIS
• more -dlfpcsu -num / pattern
  linenum fileDESCRIPTION
• More is a filter for paging through text one
  screenful at a time. This version is especially
  primitve. Users should realize that less(1)
  provides more(1) emulation and extensive
  enhancements.
• Less is a similar command with more features.

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cp

• This allows you to create a new copy of an
  existing file.
• Two mandatory arguments, source and destination.
• Source is the name of the existing file.
• Destination is the name for new file.
• If you change the contents of the new file, you
  do not change the contents of the old file.

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ln

• Allows you to create two names for one file by
  linking them, similar to a shortcut in
  Microsoft Windows.
• Two mandatory options are the source and
  destination, just like for cp.
• If you change the new version, you change the old
  version.

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mv

• This allows you to rename a file and/or move it
  to a new location.
• Two mandatory arguments, source and destination.
• Source is the name of the existing file.
• Destination is the new name and/or location for
  the existing file.
• At completion, there is only one file.

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rm

• Allows you to remove or delete a file.
• Normally, once a file is removed, it is gone
  forever!
• (UMBC has changed this and it moves the file to a
  backup directory, where you can recover it, if
  necessary. However, this is not a long-term
  option!)

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rm (contd)

• The argument(s) are a list of files to remove.
• Options include
• -i interactive, ask first (UMBC has set this as
  the default)
• -r recursive, delete the files in the
  subdirectories and the subdirectories.
• NOTE rm r directory will remove directories
  that are not empty!

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mkdir

• Used to create a new directory.
• Argument(s) is/are the name(s) of the new
  directory(ies).

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Wildcard Characters

• You will find wildcard characters useful when
  manipulating files (e.g., listing or moving
  them).
• The wildcard characters are and ?
• ? is used to represent any single character.
• is used to represent 0 or more characters.