Begin to use Linux

1. Begin to use Linux

2. Background • Linux is an operating system similar to UNIX. It runs on many different computers and was first released in 1991. • The source code is opened, that is, available at no cost to anyone who wants to modify it. • There are of different versions of Linux in the market. • Want to learn more? Go to http://www.vbird.org

3. Packages inside Linux • Apache, the most popular web server in the world. • vsftp, very secure file transfer protocol server. • Samba, let Linux become a Windows File Server. • SendMail, SMTP server • DHCP Server • Bind, DNS Server • MySQL, PostgresSQL, Database Server • iptables – A powerful firewall

4. Try Linux with Putty • Putty is a Remote Shell which can let users run his own linux shell in a remote site • Open Putty in your Windows. • Under Host Name type: ictlab.tyict.vtc.edu.hk • Protocol MUST use SSH. • Click ‘Open’ to open a ssh terminal. • Username: your student id • Password: your HKID without bracket and MUST USE UPPER CASE, e.g G123456A

5. Directories • Linux use ‘/’ as directories parser (Windows use ‘\’), e.g. /home/alan. • Files name and Directories name in Linux is case sensitive. • No Drives (A:, C: or D: ) name in Linux, you need to ‘mount’ a floppy or CD-ROM drives to a directories • All directories are started from ‘root directory /’ • Each user has his/her ‘home directory’. For user ‘alan’, by default, his home directory is ‘/home/alan’. • Home directory for Super User ‘root’ is ‘/root’

6. Commands to access Directories • All commands in Linux is case sensitive • cd /etc • Change directory to /etc • cd ~ • Change to your home directory • cd .. • Move to the parent directory of the current directory. • cd - • Move back to the previous directory you were in.

7. Commands to access Directories (2) • ls -al • List all files or directories name in long format under current directory • pwd • Display current directory's absolute path. • mkdir work • Create the directory ‘work’ in the current directory. • mkdir -p work/reports/2001/oct • Create the directory work/reports/2001/oct, creating parent (-p) directories (work, work/reports, work/reports/2001) as required without danger of overwriting existing directories.

8. Commands to access Files • cp a.txt backup/a_bk.txt • Copy the file a.txt across to the directory backup and rename it a_bk.txt. • cp -r a b • Copy the directory a into the directory b. The -r means recursive (i.e. the files and subdirectories contained in the directory, plus the files and subdirectories contained in the subdirectories, and so on). • mv a.txt work/reports • Move the file a.txt across to the directory work/reports. • mv a.txt b.txt • When you move a file to its current location, you rename it. In this case the file a.txt is renamed b.txt.

9. Commands to access Files (2) • rm a.txt • Remove the file a.txt. • rm -r work/reports • To remove a directory (even an empty one) you need to add -r. Here the directory work/reports is removed. • touch report.txt • Create an empty file (in this case report.txt), or if it already exists, update its access and modification time. • less dirs.txt • View the dirs.txt file in the less program, allowing you to view large files, line by line. (Press q to quit.)

10. Linux Installation • Press Enter for the first screen. • In each of the following steps, press ‘OK’ to proceed to the next step. (You can press ‘Tab’ to move your cursor to ‘OK’) • Select ‘English’ for language. • Select ‘US’ for keyboard. • Select ‘HTTP’ for media. • Select ‘DHCP’ for ip address.

11. Linux Installation (2) • In Server name field, enter ictlab.tyict.vtc.edu.hk • In Directory field, enter /ftp/fedora/linux/core/4/i386/os • A graphical screen will comes up. • For Language Selection, choose ‘Chinese (Traditional) • For Install Type, choose ‘Custom’

12. Linux Installation (3) • For Disk Partitioning Setup, choose ‘Manually partition with Disk Druid’ • WARNING: YOU CANNOT TOUCH /hdc IN YOUR DISK PARTITION! • Create 3 partitions in Druid: • /, file size 10000 • /home, file size 10000 • Swap, file size 1000 • Do not use /hdc! Do not use LVM! • For the password, type ‘cmuser’.

13. Linux Installation (4) • For Firewall Configuration, choose: • Enable Firewall • Check Remote Login, Web Server and File Transfer • WARNING: Disable SELinux! • For Package Group Selection, choose: • Web Server • Windows File Server • FTP Server • DNS Server • Network Server

14. Install Package with RPM • Go to http://ictlab.tyict.vtc.edu.hk/~alanpo and then download the Java Run Time (jre) RPM package to your home directory. • Open a terminal in your desktop • Type following command to install (jre): • rpm -Uvh jre*.rpm • Upgrades jre or installs the package if no previous version was found. U for upgrade, v for verbose (so you know what's going on), and h for hash (to show a progress bar).

15. More about RPM • rpm -q jre • Query RPM database, to display version of X-Chat installed. Useful for discovering if you have something installed. • rpm -qa | sort | less • To display all (-a) RPMs installed, in alphabetic order, and in the less program. • rpm -e jre • Uninstall (erase) the package webmin.

16. Users Management in Linux

17. root • All Linux distributions setup a special account called ‘root’ during installation. • The ‘root’ account gives you access to everything. • If your shell prompt ends with a hash/number-sign (#) you're logged-in as root. Normal user is a dollar-sign ($)

18. Create a new user • Only ‘root’ can create and remove user accounts. • useradd alan • Add a new user alan • His home directory will be /home/alan • passwd alan • Give this new account a password • finger alan • List the user information of alan

19. Remove a user • userdel alan • Remove user alan • userdel -r alan • Remove user alan and ALL THE FILES in his home directory

20. su - substitute user • The su command allows you to temporarily become another user, until you press Ctrl+D to logout. • su • Become root but you need to submit root’s password • su - alan • Become alan.

21. Group Management (2) • Arrange a GROUP of users can easily to apply some common policies to them. • Every user belongs to at least one group, their login group - given the same name as their user account. • groupadd students • This will create the students group. • usermod -G students john • Add user john to the group students.

22. Group Management (3) • less /etc/group • Show all groups and their members. • groupmod –n students tn_students • Rename a group • groupdel tn_students • Remove the group tn_students • groups • Display groups you belong to. • groups john • Display groups john belongs to.

23. Access Rights • Three kinds of Access Rights: • r – read, w – write, x – execute • Three kinds of people to access files: • owner, group, others • To display the owner and group a file belongs to, enter ‘ls -l’ : • -rw-rw-r-- 1 john tyict 1076 Nov 20 16:50 report.txt • First column (-rw-rw-r--) is Access Right • Third column (john) is owner • Fourth column (tyict) is group

24. Access Right (2) • Here is the break of -rw-rw-r--: • Type: - for normal files, d for directories and l for Symbolic link • For owner rw-, he/she can read, write but cannot execute the file • For group rw-, same as owner • For others r--, he/she can read but cannot write or execute the file

25. Change Access Right • chown john report.txt • Change owner of file report.txt, to john. • chown -R john . • Change owner of all files and subdirectories (i.e. -R for recursively) in the current (.) directory, to john. • chgrp tn_stundents report.txt • Change group of file report.txt, to tn_stundents. • chgrp -R tn_stundents . • Change group of all files and subdirectories (i.e. -R for recursively) in the current (.) directory, to john.

26. Change Access Right (2) • chmod a+rw report.txt • Give all users read and write permission. • chmod go-wx report.txt • Remove write and execute permission (-wx) from report.txt for group and others (go).

27. Change Access Right (3) • Permissions can also be set in octal (base 8), where read permission is a four, write is two, and execute is one. These you add up separately for user, group and other for between 000 (---------) and 777 (rwxrwxrwx), like so: