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Welcome to Linux

Welcome to Linux. A quick overview of some ideas and commands of most frequent use to programmers using Linux. Two interface options. The ‘modern’ graphical desktop interface: Objects are represented as colorful icons Users operate mainly by clicking the mouse

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Welcome to Linux

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  1. Welcome to Linux A quick overview of some ideas and commands of most frequent use to programmers using Linux

  2. Two interface options • The ‘modern’ graphical desktop interface: • Objects are represented as colorful icons • Users operate mainly by clicking the mouse • It’s ‘intuitive’ (like Macintosh or Windows) • The ‘legacy’ command-line interface: • Objects are accessed by their file-names • Users operate by typing in commands • It’s flexible and powerful, but demands knowledge!

  3. Toggle between interfaces • If your workstation is configured for the Graphical Desktop Interface by default (also known as ‘runlevel 5’), it is easy to switch to the Command-Line Interface by typing a keystroke-combination: <CNTRL><ALT>-Fn (for n = 1, 2, ..., 6) • You can return to your Graphical Desktop by typing: <ALT>-F7

  4. All Linux’s objects are ‘files’ • All ordinary files are sequences of ‘bytes’ • Some store data, others store programs • Also there are some ‘special’ files (such as ‘directories’, device-files, and pseudo-files) • Each file has a unique name • Each file has a specific ‘owner’ • Each file has a set of ‘access permissions’

  5. File ‘permissions’ Owner Group All r w x r w x w w x Legend r = ‘read access’ (1 = yes, 0 = no) w = ‘write access’ (1 = yes, 0 = no) x = ‘execute access’ (1 = yes, 0 = no) Bitmap-example: 110-100-100 Octal representation: 0644 ASCII-representation: rw-r--r--

  6. Directory Tree / /var /usr /etc /bin /boot /home Linux organizes its hundreds of thousands of files into a tree-like hierarchy. For a current Linux installation (such as Fedora Core 5), the topmost directory (named ‘/’) will typically contain only about two-dozen sub-directories.

  7. Directory Tree / /var /usr /etc /bin /boot /home … /root /parr /brooks /cruse superuser The ‘/home’ directory contains a sub-directory for each authorized user.

  8. Directory Tree / /var /usr /etc /bin /boot /home … /System.map /vmlinuz /grub compressed kernel The ‘/boot’ directory contains the files and directories that are needed to select, load, decompress, and begin executing the Linux kernel

  9. Directory Tree / /var /usr /etc /bin /boot /home … /X11 /hosts /fstab /inittab The ‘/etc’ directory stores files concerned with the system’s configuration-options.

  10. Directory Tree / /var /usr /etc /bin /boot /home … /mkdir /chown /kill The ‘/bin’ directory contains about a hundred of the most necessary and basic binary-executables (such as the programs which implement the minimal set of commands you need for system-recovery in the unlikely event of a ‘crash’ ).

  11. Directory Tree / /var /usr /etc /bin /boot /home … /local /lib /src /include /bin The ‘/usr’ directory contains about a dozen sub-directories which organize the vast majority of the various kinds files needed for a useful work-environment. Together these sub-directories contain tens of thousands of files and programs.

  12. Directory Tree / /var /usr /etc /bin /boot /home … /lock /log /spool The ‘/var’ directory contains about two-dozen sub-directories that pertain to various value-added resourses (such as system log-files or users’ email).

  13. Unique filenames • To give each file a name that’s unique, the directory-tree hierarchy is utilized: / /home /brooks /cruse /hello /hello ‘/home/cruse/hello’ ‘/home/brooks/hello’

  14. The online ‘manual’ • Linux offers online documentation for all of its commands (and for its library functions) • You type ‘man <command-name>’ to view the relevant page of this online manual • Example: $ man ls # view ‘ls’ options • Some commands have numerous options that are explained (but seldom illustrated)

  15. Command-usage examples: ‘ls’ • The ‘LiSt’ command: $ ls • $ ls # files in present working directory • $ ls / # files in the topmost (‘root’) directory • $ ls ~ # files in YOUR home-directory • $ ls –l # files with their attributes • $ ls –a # files (‘all’ including the ‘hidden’ ones) • $ ls *.c # files having the ‘.c’ filename-suffix • $ ls * # files in every immediate sub-directory • $ ls .. # files in the parent-directory • $ ls my* # files whose names begin with ‘my’

  16. My own ‘top-30’ commands • cd # Change Directory • cp # CoPy file (or files) • mv # MoVe file (or files) • rm # ReMove file (or files) • rename # RENAME a file (or files) • who # who else is using station • mkdir # MaKe a new DIRectory • rmdir # ReMove DIRectory

  17. My “top-30” (continued) • scp # Secure CoPy • ssh # Secure Shell • lpr # Line-Printer • cat # conCATenate file(s) • grep # global reg-expr printer • uname -r # shows kernel-release • ln –s # creates a ‘soft’ link

  18. My “top-30” (continued) • vi # VIsually edit a text file • gcc # Gnu C Compiler • g++ # Gnu C++ compiler • as # Assembler • ld # Linker • make # compile-and-link script • objdump -d # disassemble program

  19. My “top-30” (continued) • tar # uncompresses a file • diff # compares two textfiles • exit # terminates a user-session • time # time a program’s execution • chmod # change file’s access-mode • su # Substitute User • more # view textfile page-at-a-time

  20. Recommend keeping a ‘journal’ Some notes I find useful for reference… • For extracting a new Linux kernel release • $ tar –xvf linux-2.6.16.6.tar • For combining several files of a new project • $ tar –cvf linux-2.6.16.6.tar *

  21. Some practice exercises… • Switch from your Graphical Desktop to a Text-Mode Console Interface (6 choices) • Switch from one text-console to another • Login to that console • Type the ‘ls’ command • Log out from that console • Return to your Graphical Desktop

  22. Some exploration exercises… • Use ‘cat’ to look at one of the hidden files in your own ‘home’ directory, like this: $ cat .bash_history • Use ‘ls’ to look at the names of all the files in your own ‘Desktop’ directory, like this: $ ls -a Desktop • Use ‘cd’ to change your current directory to the ‘root’ directory, like this: $ cd /

  23. An ‘advanced’ exercise • Create a subdirectory named ‘bin’ in your own home directory, like this: $ cd ~ # ‘~’ is your home-directory $ mkdir bin # creates ‘bin’ sub-directory • Copy a program-file from a class-website, then compile it, move the executable into your ‘~/bin’ subdirectory, and finally execute it, like this: $ cp /home/web/cruse/cs630/dump.cpp . $ g++ dump.cpp -o dump $ mv dump bin $ dump dump.cpp

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