LINUX – lecture 3

• Memory Management

• I/O Subsystem Management

• File system

• Network

Memory Management

• Virtual memory concept

• Useful commands•top•free

I/O Subsystem Management

• Hierachical file system

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The file system

• /usr User program

• /var Logg files, spool files, mail, etc

• /tmp Temporary files

• /bin Linux commands

• /sbin Commands for the sys. Admin.

• /boot The kernel and boot files

• /dev Hardware devices

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The file system

• /etc Configuration files

• /home Home directories

• /lib Library files

• /mnt External file systems

• /proc Virtual directory for running processes

• Other directories as well

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The file system

• Every user has a "home"– Normally in /home, but here we use /heim

• Superuser: root.

• Other file systems may be merged with the one on the local machine using mounting

• "Everything is a file":– /dev/fd0 floppydrive

/dev/hda1 first partition on first IDE hard disk/dev/ttyS0 first serial port

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Users

• A user can only write to his/her home directory

• Root can do everything (make new users, maintain the system, read logs, clean up)

• Makes Linux safe (In other systems everyone is root!)

• A user belong to a group. (e.g "fys292")

• Every file has certain permissions (read, write and execute) for the user, the group and everybody else.

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File systems

• Linux use the "ext2" file system. (Actually we use an extention of ext2 called ext3 here)

– Include permissions and ownership for files

– ext3 is a journaling file system

• Other file systems (f. ex. FAT, NTFS, XFS) have other properties, but Linux can read all of these, and write to almost all of them.

• Because of this, Linux can easily be integrated with other operating systems.

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Rights and permissions (1)

ls -l fil*-rwxr-xr-x 1 espen kjeks 65 jan 23 23:06 fil1-rw-r--r-- 1 espen kjeks 65 jan 23 23:06 fil2-rw------- 1 espen kjeks 65 jan 23 23:06 fil3-rwxr--r-- 1 espen kjeks 65 jan 23 23:06 fil4drwxr-xr-x 4 espen kjeks 4096 des 26 15:31 fil5

drwxr-xr-x d = directoryr = read permissionw = write permissionx = execute permissionspecial|user|group|others

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Rights and permissions (2)

-rwxr-xr-x 1 espen kjeks 65 jan 23 23:06 fil1– "espen" can read, write, execute.

– Users in the "kjeks" group can read and execute

– Others can also read and execute the file.

-rw-r--r-- 1 espen kjeks 65 jan 23 23:06 fil2-rw------- 1 espen kjeks 65 jan 23 23:06 fil3-rwxr--r-- 1 espen kjeks 65 jan 23 23:06 fil4drwxr-xr-x 4 espen kjeks 4096 des 26 15:31 fil5

– You need write permission to a directory to deletefiles in it.

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Why permissions?

• More secure:– Can't delete files you're not supposed to...

– Can't view files you shouldn't

• Easy to group users together:– Easy file sharing between groups

– Only group can read/write files

• Every file has an owner

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Changing permissions (1)

• Every new file gets a default set of permissions, most often: -rw-r--r--

• This file cannot be executed directly!

• Change so that owner can execute:chmod u+x filename

– "User: add execute permission"

– u = user, g = group, o = others, a = all

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Changing permissions (2)

• To make a file executable and writeable (be careful...) by your group:chmod g+wx filename

• Restrict permissions with -chmod a-x filenamechmod go-r filename

• root can of course read the file anyway

• Permissions can also be set absolute -not just relative; chmod 600 filename

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STDIN and STDOUT

• "What is input, and where does it go?"

• Usually, the keyboard is standard in, the monitor is standard out:– ls -l takes keyboard input, and views the file list on the

screen

– echo "Hello there" also takes keyboard input and views the result on the screen.

• Many commands use STDIN and STDOUT, but we can often "force" them to not use these

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Redirection (1)

• Why don't we want ls -l to display its output on the monitor?

– Your friend wonders which .mp3 files you have. You have them all in a directory, and want to e-mail him a list of the files. There's always cut'n'paste, but...

– The system admnistrator wants to keep a list of what processes are running on the machine

• ls mymp3s > list-of-mp3s.txt• ps -aux > list-of-processes.txt

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Redirection (2)

• Redirection to a device (here: a printer): ls mymp3s > /dev/lp0

• Redirect standard input:Assume there is a file "dirs" containing names of directories with files. We want ls to view the contents of all these:ls < dirsls < dirs > listoffiles.txt

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Redirection (3)

• Using ">" creates/overwrites a file. Use ">>" to append to a file:ls newmp3s >> list-of-mp3s.txt

• There is also something called "Standard error". This is also usually the screen, but can be useful to "suppress" in scripts. Then we can redirect it to /dev/null, which is the Unix/Linux "Recycle bin":ls -l /crap >& /dev/nullls -l /crap >& error.msg

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Pipes

• A "pipe" is used to direct the output of one command to act as input for another command.

• How many new mp3's do you have in "newmp3s"?ls newmp3s | wc

• To many files in the directory to get the overview?ls -l newmp3s | more

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"Wild-characters"

• Used to denote "more than one character":– ? is a replacement for one (and only one character)– * is a replacement for any number of characters

• Useful with ls:– ls -l *.gif lists all files ending with ".gif"– ls -l /usr/bin/pi?? lists all files in /usr/bin starting

with "pi" and having four characters in total.

» "pine" and "pico" will match, but not "pinky"

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Some useful commands (1)

• Change directory: cd– cd .. One directory up– cd /usr/local Go to /usr/local– cd Go "home"

• List files: ls– ls -l List with long format– ls -a/tmp List hidden files in

/tmp directory– ls -lt Sort by time

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Some useful commands (2)

• Where am i? pwd– pwd Prints working directory

• Delete file: rm– rm myfile.html Removes the file– rm -rf ~/html Removes all files in

/home/user/html without prompting– rmdir myfiles Removes directory

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Some useful commands (3)

• Make directory: mkdir– mkdir webpages Makes a directory

• Move/rename file: mv– mv oldname newname Renames file– mv file /newplace Moves file

• Print files: lpr– lpr -Pps2 file.txt Print text file to ps2– lpr -Pps4 file.ps Print PostScript file to ps4

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Networking

• To communicate, we must have network protocols

• A protocol is a set of rules of how the communication should take place

• TCP/IP "Transmission Control Protocol/Internet Protocol" is the most common and best known.

• UDP, ICMP, ARP, SMTP, RIP, SLIP, PPP, POP

• TCP/IP is the language of Internet and Intranets

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TCP/IP

• At the lowest level communication is just current running in wires

• A network interface card (NIC) produces these signals. A NIC has an unique address called "hardware address". Ex: 00:40:33:57:ED:9F

• We assign an IP address to a network card, for example 129.177.40.40

• We have human readable aliases for the IP numbers; 129.177.40.40 is goliat.ift.uib.no

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Using TCP/IP

• File transfer: sftp

• Remote login: ssh

• Web: http

• News: nntp

• E-mail: pop, smtp

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Logging on

luna~> ssh merkurespen@merkur's password:Last login: Wed Feb 13 22:56:01 2002merkur~>

– ssh has replaced telnet and rlogin, because ssh is more secure

– There are also replacements for ftp; scp and sftp

– Anonymous ftp; public servers

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Our network

• Allows incoming ssh/sftp/scp from all nodes inside our institute.

• Outside connection has to go via portal1.ift.uib.no.

• Does not allow much else unless you are at our institute.

• ssh/sftp/scp use encryption

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Starting programs (1)

• Some computers are fast

• Some computers have special software

• Some computers are familiar to you

• Some computers run services we want

• ...so we want to be able to log in, and run whatever we want!

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Starting programs (2)

• Log in and start matlab:

bagdad-01> ssh merkur.ift.uib.noespen@merkur's password:Last login: Wed Feb 13 22:56:01 2002merkur~>matlab &

• ssh clients are also available for Windows, allowing you to log in from everywhere.

• This is why you should learn a console basede-mail program and text editor.

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Some commands

• See who's logged in:– w– who– finger

• What is the machine running: uname -a• What jobs are running: ps -aux