linux crash course

ls: LiSt files• Used to list files contained in a directory • Can narrow the search using pattern matching • Examples – ls  displays ‘all’ the files in the directory – ls cats  display

Linux Crash Course

Selected snippets from

CIS52

Long ago, in a galaxy far away …

• Computing power was costly

– UNIVAC cost $1 million

• CPU time was a premium

– Most mainframes had less computing power than

a calculator on the shelf at Wal-Mart

• Jobs were submitted into a queue

– Only one process at a time – scheduling

nightmare

What was needed

• Allow multiple users to access the same data and resources simultaneously

• Service many users more cheaply than

buying each their own machine

• The ability to run multiple processes at once

• And do so while maintaining user

segregation and data integrity

Enter Unix, pride of Bell Labs

• Originally written in PDP-7 assembly

language by Ken Thompson

• To make it work on multiple architectures (portable), Thompson rewrote Unix in B

• Dennis Ritchie developed C, and with

Thompson, rewrote Unix in C

What was so great about it?

• Multiuser

• Multiprocess

• Non-proprietary

• Economical for business

• Initially given for free to colleges and

universities (great tactic!)

What happened?

• UNIX became commercialized

• Proprietary code, specialized distributions

• Costs started to become a hindrance

• So … let’s make our own Unix …

• Richard Stallman decides that there should

be a free version of Unix available

• Forms the GNU project – GNU’s Not Unix

• Writes all of the system programs and

utilities to mimic Unix variants

• Everything but a kernel (Hurd)

Final piece

• Universities trying to teach Unix and OS

design can’t afford Unix

• Andrew Tanenbaum writes Minix

• Linus Torvalds, dissatisfied with Minix, writes his own – Linux

• Torvalds has a perfectly functioning kernel – but no system programs

• Finds a perfect candidate in GNU

• Together, the operating system world was

changed dramatically

• Many useful utilities built-in

• Rich networking support

Consoles and terminals

• Monitor, keyboard (and maybe mouse) attached

to the box

• The console often locked away in a closet or

server farm somewhere

• Terminals usually found in mainframe

environment

• Recently ‘thin clients’ gaining popularity again

Terminal Emulation

• Using a separate system, connect a virtual

terminal to the server

• telnet, ssh, X Windows

• Most common way to interact with a

Linux/UNIX machine

• Ubuntu – Applications->Accessories->Terminal

The Shell

• Command interpreter

• Translates commands issued by user into commands sent to the kernel

• Common shells: bash, tcsh, csh, zsh, ksh

• Linux default is bash (Bourne Again Shell)

Administrative privleges

• root or superuser

• Full read/write access to filesystem

• Can execute privileged commands and programs

• Use sparingly and with extreme caution

Admin Priv, con’t

• We’re using Ubuntu, which treats root in a unique fashion

• Don’t logon as root

• To execute privileged commands:

– sudo [command] or gksudo [command]

– Will prompt for your credentials – are you sure??

Getting help

• Most GNU commands and utilities have built in help and usage information

• help (sometimes -h or -help)

• Too much information? Pipe results to less or

more

– ls help | less

man Pages

• man program_name

• Displays online documentation, formatted with a pager

• SPACE to advance, q to quit

• Depending on the system sometimes you can also

use PAGE UP/DOWN

Typing Commands

• Beware of special characters

• Characters that have special meaning to the shell

• Shell expands, modifies and interprets

special characters before issuing the

command

Special Characters

• & ; | * ? ‘ “ ` [ ] ( ) $ < > { } ^ # / \ % ! ~ +

• Plus whitespace (tabs, spaces, newlines)

• Do not use these in filenames unless you

have to

• To use them, either put in single quotes,

or proceed with a backslash

– ls ‘filename with special chars!!’

– ls \[cat\]

• Linux & Unix come with thousands of utilities

• Some used explicitly, others implicitly

• Some text-based, some GUI, some both

Some tips before we start

• Tab completion

– When typing a filename or command name, you can type the first few letters then hit TAB to auto- complete the command

• Command history

– Use the up and down arrow keys to cycle

through recently executed commands

– You can edit them before issuing again

ls: LiSt files

• Used to list files contained in a directory

• Can narrow the search using pattern

matching

• Examples

– ls  displays ‘all’ the files in the directory

– ls cats  displays the file cats in the directory – ls ca*  displays files starting with ‘ca’

cat: catenate a file

• Displays the contents of one or more files

• Beware – don’t try with binary files

• Examples

– cat myfile  displays contents of myfile

– cat file1 file2  displays contents of file1

followed by contents of file2

cp: CoPies files

• Usage: cp sourcefile destinationfile

• Creates a copy, leaves sourcefile intact

• If destinationfile exists, it will be overwritten

– Unless you use –i option

• Example:

– cp myfile myfile.backup

mv: MoVe files / change name

• Usage: mv existingfile newfile

• Just like cp, can overwrite with –i option

• Renames a file, which can also move it to another directory

• Examples:

– mv myfile foshizzle

– mv /dir1/myfile /dir2/myfile

Editing Files

• gedit filename

– Similar to notepad in Windows

• Do you have rights to edit?

– If a system/service file probably not

– gksudo gedit filename

– We’ll have to edit some config files manually; mostly we’ll try and use Webmin

Hierarchical Filesystem

• Directories can contain other directories

and/or ordinary files

• Concept different from reality – in

implementation everything is a file

• Directories, devices, named pipes, ordinary files – all really just files

• Root directory

• Subdirectories

• Parents, children

• Each file within a directory must have a

wholly unique filename

• Can be up to 255 characters – make them longer to avoid confusion

• Special characters must either be escaped out (using backslash) or in quotes

• Only illegal characters are / and carriage return

Hidden Files

• To make a file hidden, start it with a period

– Ex plan

• A normal ls will not show hidden files

• Use ls –a to reveal ALL files

• Startup files, containing configuration

settings for your account, hidden

mkdir – create directory

• Syntax: mkdir directory

• Directory can be a relative or absolute

pathname (we’ll get to that in a minute)

• You can use ls –F to show directories with a

forward slash at the end of the name

• If using a color terminal, directories will be a different color than ordinary files

Working Directory

• The directory you are currently working in

• pwd will tell you what your working directory

is

• Helpful to know when using relative

pathnames (again, coming up)

Home Directory

• Not to be confused with working directory

• The directory you start in when you first logon

• Most users it is /home/username

• For root, it is /root

• Can be changed by system administrator

cd – change working directory

• Syntax: cd [directory]

• Again, directory can be absolute or relative

• If no argument given, changes working

directory back to your home directory

Absolute Pathnames (finally)

• Absolute pathname for a file gives the file’s location relative to the root of the filesystem

• Sometimes long

• Ex: /home/jhowell/Assignment1/animals

• Shortcut: ~ represents your home directory

• So the above could also be

~/Assignment1/animals

and Directories

• is an alias for the working directory

• is an alias for the parent of the current

Common Directories

• / (root) – root of the filesystem

• /bin – essential system binaries (commands)

• /boot – files for the bootloader

• /dev – device files

• /etc – system configuration files

• /home – user home directories

• /lib – standard libraries and modules

Common con’t

• /mnt – mount point for temporary filesystems

(floppies, CD-ROMs, non-native partitions)

• /opt – optional add-on software

• /proc – kernel and process information

• /root – root’s home directory

• /sbin – essential system binaries

• /tmp – temporary space (not swap)

Common con’t

• /usr – common area for data / program users

use frequently

• /var – frequently changing data like system

logs, caches, spools and mailboxes

• That said, all these can reside on the same partition

• Only / and a swap partition required

• Use a ls –l (for long view) and you might see

something like this:

drwxr-xr-x 2 jhowell jhowell 4096 Aug 18 15:46 Desktop

-rw-rw-r 1 jhowell jhowell 0 Sep 4 18:08 myfile

drwxrwxr-x 2 jhowell jhowell 4096 Aug 22 15:32 public_html

Type

of file

File Permissions

# of links

chmod – CHange MODe

• Changes permissions

• Syntax: chmod [ugoa][+-][rwx]

• Ex: grant everyone (all) read and write

chmod a+rw myfile

• Ex: remove execute permission for other

chmod o-x myfile

• root can still read and write to files without

read and write permissions