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LINUX – lecture 3

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. The file system. /usr User program /var Logg files, spool files, mail, etc

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LINUX – lecture 3

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  1. LINUX – lecture 3 • Memory Management • I/O Subsystem Management • File system • Network

  2. Memory Management • Virtual memory concept • Useful commands • top • free

  3. I/O Subsystem Management • Hierachical file system

  4. 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

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. 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 fil4 drwxr-xr-x 4 espen kjeks 4096 des 26 15:31 fil5 drwxr-xr-x d = directory r = read permission w = write permission x = execute permission special|user|group|others

  10. 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 fil4 drwxr-xr-x 4 espen kjeks 4096 des 26 15:31 fil5 • You need write permission to a directory to deletefiles in it.

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. "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"

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

  25. Using TCP/IP • File transfer: sftp • Remote login: ssh • Web: http • News: nntp • E-mail: pop, smtp

  26. 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

  27. 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

  28. 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!

  29. 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.

  30. Some commands • See who's logged in: • w • who • finger • What is the machine running: uname -a • What jobs are running: ps -aux

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