Unix Essentials

... or everything I can fit in 2 hours!

I am your geeky host, Jordan Sissel.

Obey me.

If you have questions during the presentation, ask them and I will answer them. However, keep in mind that I may be answering your question soon in the slides, anyway.

Mostly, try to focus questions on confusion about the material, rather than focusing on "what if foo?" type questions. Write down other questions and save them for question breaks, if you can. At the end of this seminar, you should feel at least mildly comfortable in a Unix system environment.

• What is Unix?
• Basic Environment
• The Shell
• The File System
• Graphical Environment

Lets start by relating to what you already know:

• If you use Windows: Unix is different.
• If you use OSX: Unix is different.

What does different mean?

It's mean and scary... or is it? Unix environment components

• Getting access
• Graphical programs
• The Terminal
• The Shell
• Command-line programs
• The File System

• Local access - usually graphical
• Remote access - usually terminal-based

An account is a username (and password) that identifies you and lets the system decide if you are allowed access. Features of local access:

• Graphical Interface
• Easy access to local graphical programs.

Let's login now! (if you haven't already) Features of remote access:

• Terminal (text) Interface
• Access to graphical programs limited

• SSH
• Telnet (maybe)

However, we don't know how to start them yet...

We'll come back to this. Pros and cons:

• Pro: Lots of interface environments = diversity
• Con: Lots of interface environments = diversity

X simply provides a means to draw windows. Window managers are used to draw window borders and provide other features.

What does X look like? Back to business...

Moving from Windows/OSX to Unix, you may feel more comfortable using Desktop Environment software. Such software includes:

• GNOME
• KDE
• Xfce

It is also the standard environment on Solaris.

The project aims to provide "an intuitive and attractive desktop for users" (quoted from gnome.org)

If you have never used Linux or Solaris, GNOME should help you feel more comfortable when using them. You'll need a mouse and a keyboard.

The Applications button is similar to the 'start' button in Windows.

The desktop and its icons should behave similarly to OSX and Windows. Moving Windows:

• Windows can be dragged by holding ALT while left-click dragging them.
• Windows can be resized by holding ALT while middle-click dragging them.

• Most text is automatically copied when you select it
• Most interfaces understand "middle click means paste"
• This is called "Grab and Splat" and is very useful

• Right-click on the desktop
• Select 'Change desktop background'
• Pick a background
• Resume life.

Pick something to run. How about Minesweeper (GNOME Mines)? You can add this (or any) program to the quicklaunch panel:

• Right-click on the panel
• "Add to panel"
• "Launcher from menu"
• Pick the application
• Take a nap

You may want to add this application to the panel at this time. It's useful to have within short reach. A terminal provides a means by which to allow you to easily interact with your shell.

The terminal knows things about the window size, input/output features, colorization, cursor movement, etc. It allows you to provide input to your shell (and other programs).

Input using the keyboard. GNOME's terminal program, called gnome-terminal, is configurable. You can define profiles which set:

• foreground (text) and background color
• font family and size
• scrollback buffer
• a few other things

I like white text on black background, as it's very easy to read. A shell is a text-based interface to your system.

Most shells provide a common subset of features:

• Basic line editing
• Command path list
• File and Command completion
• Configurable prompt

Ctrl+L

Clear the screen

Ctrl+W

Delete the previous word (starting at cursor)

Ctrl+U

Clear the line

Left and Right arrow keys

Move the cursor

Up and Down arrow keys

Command history traversal

Try this the 'ls' command. 'ls' will list directory contents. Most shells will complete file and command names, when possible, when you tell them to.

For instance, if I execute 'ls' to see the directory contents: Typing 'he' and pressing Tab will make the shell automagically complete your word to 'hello' becuase it sees that 'hello' is a file, and starts with 'he' This will run less and start you viewing the file specified. You start at the top of the file. Navigation:

Arrow keys

Move around

Page Up/Page Down

Take a guess!

/foo

search for 'foo' in the document

?foo

reverse search for 'foo' in the document

n

find next

N

find previous

• Most OS's will come with documentation.
• View documentation with the "man" program

Searching in 'less' will help you find that you need in a manpage. The next sections will introduce several basic commands.

If you have questions about what was previously covered, feel free to ask them now.

• File system commands
• Data commands
• Common shell commands

Usage: pwd Example: nfwire(~/projects) % pwd /home/jls/projects 'ls' lists directory contents.

Usage: ls [-laRF]

-l (lowercase L)

Specify long format

-a

Show "hidden" files

-R

Recurse through directories

-F

Identify special files

Usage:

-f

force removal (do not ask)

-i

ask before removing any file

-r

recurse through directories

Usage:

• Sources can be files or directories to be moved.
• Destination can also be a file or directory name
• Only a directory is allowed if multiple sources specified

Directories must be empty before you can delete them.

Usage: rmdir directory ... Example: Change mode (access permissions). Usage: Modes are 3-tuple octal values: XXX. First letter (left) is owner permissions, middle letter is group permissions, last (right) letter is world permissions.

• 400 : Allow read by owner.
• 200 : Allow write by owner.
• 100 : For files, allow execution by owner. For directories, allow the owner to search in the directory.
• 040 : Allow read by group members.
• 020 : Allow write by group members.
• 010 : For files, allow execution by group members. For directories, allow group members to search in the directory.
• 004 : Allow read by others.
• 002 : Allow write by others.
• 001 : For files, allow execution by others. For directories allow others to search in the directory.

755

Owner: read, write, execute. Group: read, execute. World: read, execute

644

Owner: read, write. Group: read. World: read

600

Owner: read, write. Group: nothing. World: nothing

The following file has permissions 644: -rw-r--r--

cat

concatenate files

grep

search file contents

diff

compare files and show differences

sort

sort data

uniq

find unique elemenets

find

find files

file

identify a file by its data

Usage: Patterns are any valid regular expression. Plain words are valid :)

Example: Compare files and show differences.

Usage: Example: Sort data the way you like it.

Usage:

-n

Sort numerically. That is, '99' < '100'. Normally, '99' comes after.

-r

Reverse sort order

Usage:

-c

Display total counts for each unique hit

Usage: Some valid expressions include:

-name '*.jpg'

Print files ending in '.jpg'

-name 'MyClass.java'

Print files called 'MyClass.java'

Usage: Examples:

• history
• echo
• export

NOTE: The specific usage of this command varies by shell

Generally, typing 'history' is what you'll probably want. it shows some recent commands. Print out the arguments. Usage: Example: Declare a variable as one to be exported to the environment to new commands.

Usage: Example: Meaningful environment variables:

• PATH - a list of paths from which to search for programs
• EDITOR - default editor to use
• PAGER - default pager to use

A common change to make in your shell is to customize your prompt. If you are using Bash as your shell, then you need to configure the PS1 variable.

For instance, to have your prompt be: hostname(pwd) % You will want to "run" this in your shell: PS1="\h(\w) % " Technically you aren't 'running' anything so much as setting a variable. Many shells have scripting languages or concepts.

• Processes are running commands.
• Identified by a unique id, called a process id, or pid.

• ps
• kill
• pkill

Usage (Linux/Solaris):

-e (linux/solaris)

list all processes running

-f (linux/solaris)

full (longer) listing information

-o fmt (bsd/linux/solaris)

Customize the output format of ps. Read the manpage for formatting

Usage (BSD):

-a (bsd)

show all processes

-x (bsd)

show background processes too

-o fmt (bsd/linux/solaris)

Customize the output format of ps. Read the manpage for formatting

Examples: Send signals to processes (Like the KILL signal). Usage: Valid signals are:

TERM (kill -TERM)

the terminate signal, process should die off cleanly

INT (kill -INT)

the interrupt signal. Hitting Control+C sends this aswell

KILL (kill -KILL)

An unavoidable signal. The process will die without cleanup

We are running 'cat' in another terminal. We'd like to destroy it. Wait. What's pgrep? Find or signal a process by attribute. What?

• pgrep lets you search for processes.
• pkill lets you signal processes.

• Jobs are processes running from your shell
• You can have multiple jobs executing at the same time
• Control+Z, backgrounding, bg, fg, jobs
Example:

• Jobs can be sent to the background with the 'bg' command
• Bring a job to the foreground with 'fg'
• Kill a job by running 'kill %1' where '1' is the job number
• Kill the recent job with 'kill %'

/

Root directory

/bin

Fundamental user utilities

/sbin

System and administrative programs

/usr

majority of user utilities and applications

/usr/bin

common utilities, tools, and applications

• Data pipes
• Data flow redirection (still, like pipes)

This philosophy of directable output is arguably Unix's most powerful feature.

Example situation:

• You want to see the top 10 largest directories in your home directory
• 'du' command will show file/directory sizes
• 'sort' will sort output
• 'tail' will display the last N lines of output

du -s */

Calculate total size of files inside each directory

sort -n

Sort output numerically

tail -10

display last 10 lines of output

This is why pipes are powerful. Instead of needing a special program to show the top 10 largest directories, you can use 3 already-written programs and pipe outputs. File redirection is very similar in principle to pipes.

You use '<' and '>' to direct data from files to/from input/output.

ps -ef > bar

Direct standard output of 'ps -ef' to the file 'bar'

sort < bar

Direct input for 'sort' from file 'bar'

ps -ef >> bar2

Append output of 'ps -ef' to the end of file 'bar2'

*

Match anything

?

Match a single character

{x,y.z}

Match 'x', 'y', or 'z'

/ (trailing)

Match directories only

echo */

one/ three/ two/

echo {a,b}?

aa bb

ls *.txt

bar.txt foo.txt

• tar - file archiving
• gzip - gnu compression utility
• bzip2 - another compression utility

• tar, the command, is used to create and extract "tar" files.
• tar files are like Zip files, without compression

bzip2 is another free compression utility. It often compresses text better than gzip.

tar often supports a '-z' option to have it automatically gzip/gunzip the data before creating or extracting your tar file. The same '-z' flag can be used with extraction, '-x'.

• du - disk usage
• quota - display quota information

-h

Human readable (mb, kb, gigs, etc)

-s

Report total sum for each of specified files/directories

-v

verbose output

Soft quota

warnings are issued about being over quota.

Hard quota

New data cannot be written to any files, some programs may fail to work

*.core files (or just 'core')

memory dumps from programs that crashed

*.class files

Class files generated by javac. You may not need these anymore

Firefox web page cache

RIT has a fast net connection. When you're running low on quota, disable or lower your web cache size

Ways of logging in using SSH:

• The normal 'ssh' command on any modern unix system
• PuTTY from Windows (free program)
• SSH.com's SSH Client for Windows
• OS X comes with 'ssh' which can be run from any terminal program

Neat Feature: You can run commands instead of getting a shell: ssh username@hostname 'your command' Such as: ssh jls9398@grace.rit.edu 'uptime' Download PuTTY from the PuTTY website.
(Google for "putty")

It is very easy to use. Run it, type the hostname, and go. PuTTY acts as a terminal AND an ssh client. This workshop would not have been possible without the following people:

• Mike Dumont (CSH) - Planning, scheduling, organization
• Gary Scarborough (IT) - Software and Systems

I'll be happy to entertain any question