1. RH033 Redhat Enterprise Linux Essentials

2. Unit 1 • Redhat Linux Essentials • Overview

3. Redhat Enterprise Linux • Certified with Leading OEM and ISV Products • ISV  Independent Software Vendor • OEM  Original Equipment Manufacturer • ABI/API Compatibility • Application Binary Interface • Application Programming Interface • ELF  Executable and Linking Format • LSB  Linux Standards Base • BEA  BEA System Inc, San Jose, California. “Think Liquid” • HPC  High Performance Computing

4. Unix Flavors • UNIX from AT&T, at Bell Labs, in 1969. • AIX from IBM • HP/UX from Hewlett-Packard • SunOS (Later Solaris) from Sun • IRIX from SGI (Silicon Graphics)

5. Unix Principles • Everything is a file. • Including hardware • Configuration data stored in text • Small, single-purpose programs • Avoid Captive User Interfaces • Ability to chain programs together to perform complex tasks.

6. GNU Project / FSF • GNU Project started in 1984 • Goal : Create “Free” UNIX clone • By, 1990, Nearly all required userspace application created. • gcc, emacs etc. • Free Software Foundation • Non-profit Organization that manages the GNU Project • Four Freedoms • http://www.gnu.org/philosophy/free-sw.html

7. GPL – GNU General Public License • Primary license for Open Source Software • Encourages free software • All enhancements and changes to GPL-software must also be GPL • Often called “CopyLeft” • “All rights Reversed” • http://www.gnu.org/copyleft/gpl.html • X Window System, has it’s own T&C. • BSD code need to be abide the terms of Berkeley Software Distribution. Visit http://www.bsd.com

8. Linux Origins • Linux Torvalds • Finish College Student in 1991 • Created Linux Kernel • When Linux Kernel Combined with GNU Applications, complete free UNIX-like OS possible.

9. Why Linux? • Fresh Implementation of UNIX APIs. • Open Source Development model. • Supports wide variety of hardware. • Supports many networking protocols and configurations. • Fully supported. • Linux is a UNIX-like OS. • Multi-user and Multi-tasking. • Wide hardware support. Checklist. • Fully Supported.

10. Redhat Enterprise Linux • A distribution of Linux • Custom version of a recent Linux Kernel. • Utilities and applications. • Installation and configuration software • Support available. • RHEL includes installation and configuration software, a patched and rigorously tested recent version of the Linux Kernel, and thousands of utilities and applications. • gdm is the default display manager for RHEL.

11. Recommended Hardware Specifications for RHEL • Pentium Pro or better with 256 MB RAM • Or • 64-bit Intel/AMD with 512 MB RAM • 2-6 GB Disk Space • Bootable CD • Other processor architectures supported • Itanium 2, IBM Power, IBM Mainframe.

12. Virtual Consoles • Virtual Consoles are available through CTRL – ALT – F[1-6] • If X is running, it is available as CTRL – ALT – F7 • The virtual consoles enable a user to have multiple logins even when not using an X Window system. • You can scroll at the virtual consoles by using SHIFT-PAGEUP and SHIFT-PAGEDOWN. The scroll buffer is stored in video memory, so if you are running a graphical program such as X, the scroll buffer is lost.

13. The Xorg GUI Framework • The goal of X.Org include a faster and more open development model than Xfree86, support for a wide variety of video cards and input devices and the development of a highly modular and flexible graphical framework for Unix and Linux. • http://xorg.freedesktop.org • Or • http://www.x.org/wiki • X Client activity that spawns an X server event informing the web browser to send an HTTP request to the link’s target ( or anchor). You do not really see the X server, but X clients. • X provides the data I/O infrastructure for X clients, like a human nervous system, it sends messages when touched by client activity. • An X Client running on one system can display on any X server running on any operating system, if sufficient access is granted. • For each managed display, this socket is /tmp/.X11-unix/X# where # is 0 to the greatest number of permitted connections.

14. Xorg Graphical Environments • Collections of applications that provide a graphical working environment with a consistent look and feel. • GNOME (GNU Network Object Model Environment) The default desktop environment. • KDE ( K before L)  Environment based on the Qt toolkit.

15. Starting Xorg • Nothing needed if system boots to a graphical login. Just authenticate. • If system boots to a virtual console login, Xorg must be started manually. • Run startx to manually start Xorg. • Changing Password. • At least 6 but no more that 255 characters. • Other criteria depends on particular OS.

16. Unit 2 • Running Commands and Getting Help

17. Getting Help • --help • whatis -- with makewhatis • man • info • /usr/share/doc/html/en/ • Software source code • Documentations

18. Running Commands • Commands have the following syntax: • Command [ options] [arguments] • Each item is separated by a space. • Options modify the command’s behavior • Word options usually preceded by “--” • Single-letter options usually preceded by “-” • Can be passed as “-a –b –c “ or “-abc” • Arguments are filenames or other date needed by the commands.

19. The –help option • Anything in straight braces ([]) is optional. • Anything followed by “…” represents an arbitrary-length list of that thing. • If you see multiple options separated by pipes (|), it means you can use any one of them. • Text in straight brackets(<>) represents variable date. So <filename> means “insert the filename you wish to use here”. • Sometimes, such variables are simply written in all CAPS.

20. The man Command • The collection of all man pages on a system is called the Linux Manual. The Linux is divided into sections, each of which covers a particular topic, and every man page is associated with exactly one of these sections. • The sections are: • Manual Sections. • 1 User Commands • 2 System Calls • 3 Library Calls • 4 Special Files • 5 File Formats • 6 Games • 7 Miscellaneous • 8 Administrative Commands • man and man –k commands

21. The info command • info pages are structured like a website. • Each page is divided into “nodes”. • Links to nodes are preceded by “*”. • info [<command>] • If you run info with no arguments you will be presented with a list links to the top nodes of every available info page.

22. Navigating info Pages • While viewing an info page • Navigate with arrows, pgUp, pgDown • Tab Move to next link • Enter Follow link the cursor is on • n/p/u View next/previous/up-one node • s[<text>] Search for text (default: last search) • q Quit Viewing page • If you prefer the navigation keys used by man, such as using “/”, “n” and “N” to search, you can start info with the –vi-keys arguments.

23. Extended docs • /usr/share/doc • http://www.redhat.com/docs

24. Miscellaneous • ‘man –f foo’ is the same as ‘whatis foo’. • If your system has just been installed, neither man –f nor whatis will work until an administrator runs makewhatis. • ls –lh

25. Unit 3 Browsing the File system

26. Linux File Hierarchy Concepts • Files and directories are organized into a single-rooted inverted tree structure. • Filesystem begins at the “root” directory, represented by a lone “/” (Forward slash) character. • Names are case-sensitive. • Paths are delimited by “/”. • A user’s path is a list of directories that are searched for commands typed at the command line.

27. Some Important Directories • The essential binaries necessary to boot and maintain the system reside in /bin for regular binaries and /sbin for system binaries. • Non-essential binaries, such as graphical environments, web browsers, office tools and so forth, are installed in /usr/bin and /usr/sbin. • On a newly installed system, there will also be /usr/local/bin and /usr/local/sbin directories, but they will be empty. • CD-ROM is mounted under /media/cdrom folder. • Filesystems that are on non-removable media but are not part of the RHEL, hierarchy are usually mounted under /mnt. • Visit http://www.pathname.com/fhs

28. Other Important Directories • /etc -System Configuration Files • /tmp -Temporary files • /boot -Kernel and boot loader • /var and /svr -Server data • /proc and /sys -system Information • The lib directories • /lib, /usr/lib, /usr/local/lib

29. On Folders • Once a day the system automatically deletes any files over seven days old in /tmp and it’s subdirectories. • The /var directory contains regularly-changing system files such as logs, print spools and email spools. • In the future, server data may be moved to the /srv directory so that /var only contains logs, spools and so forth. • Each shell and system process has a current working directory (cwd).

30. File and Directory Names • Names may be up to 255 characters. • All characters are valid, except the “/”. • It may be unwise to use certain special characters in file or directory names. • Some characters should be protected with quotes when referencing them. • Names are case sensitive. • Example: MAIL, Mail, mail and mAiL • Again, possible but may not be wise. • To access a file with name contains special characters, enclose the filename in quotes.

31. Absolute Pathnames • Absolute pathnames begin with a slash (/) • Complete “road map” to file location. • Can be used anytime you wish to specify a file name. • To change to your previous working directory • $ cd – • A dash (-) represents your previous working directory. It’s a handy shortcut to use to switch back and forth between two directories.

32. Copying Files and Directories • cp – copy files and directories • Usage: • cp [options] file destination • More than one file may be copied at a time if the destination is a directory. • cp [options] file1 file2 dest • If final argument is an existing directory, a copy of the source files are placed in that directory with the same name as the source. • Otherwise, the destination is interpreted as a file name, and a copy of the source file is created with that.

33. On Copying • When copying a single file to a destination, cp first checks to see if a directory exists with the destination name. • If it does, a copy of the source file is placed there with it’s original name. • If not, the destination is assumed to be a new file name, and a copy of the source file is made with the destination name.

34. Moving and Renaming Files and Directories • mv – move and/or rename files and directories. • Usage: • mv [options] file destination • More than one file may be moved at a time if the destination is a directory. • mv [options] file1 file2 dest • If the destination directory does not exit, the slash will cause the command to fail with an error message. • If the destination directory does not exist (but the destination pathname is valid), the source directory will be moved to the destination directory with the new name.

35. Creating and Removing Files • rm – remove files • Usage: • rm [options] filenames… • -i – interactive • -r – recursive • -f – force • touch – create empty files or update file timestamps • The –r option tells rm to remove files recursively and thus it will delete directories and their contents. • There is no way to undo the effects of rm, except to restore from a backup. • rmdir will only remove empty directories. To remove a directory and it’s contents, use rm –r.

36. Using Nautilus • Gnome graphical Filesystem browser • Can run in “Spatial” or “Browser” mode • Accessed via … • Desktop icons • Home: Your home directory • Computer: Root Filesystem, network resources and removable media. • “File Browser” option on Application menu. • Typing CTRL-SHIFT-w closes all parent windows. • “Spatial” or “Browser Mode” can be edited.

37. Moving and Copying in Nautilus • Drag and Drop • Left-button: Move on same filesystem, copy on different system. • Ctrl-Left-button : Always Copy • Ctrl-Left-button: Ask whether to copy, move or create symbolic link (alias) • Context Menu • Right-click or rename, cut, copy or paste.

38. Determining File Content • Files can contain many types of data. • Check file type with file before opening to determine appropriate command or application to use. • Syntax • file [options] filename(s) • fileprints its best guess of the type of data contained in a file whose name is given as an argument. It bases it’s guess on a comparison of the contents of the file and the patterns and offsets in it’s reference file, /usr/share/magic.

39. Viewing an Entire Text File • Syntax: • cat [options] [files..] • Contents of the files are displayed sequentially with no break. • Files display “concatenated”. • -A Show all characters, including control characters and non-printing characters. • -s “Squeeze” multiple adjacent blank lines into a single blank line. • -b Number each (non-blank) line of output.

40. Viewing Text Page by Page • Syntax: • less [options] [filename] • Scroll with arrows/pgUp/pgDown • Useful commands while viewing: • /text --search for text • n --next match • v -- open file in text editor. • less is the pager used by man

41. On less • Less navigation commands: • <space> move ahead one full screen • <return> move ahead one line • <Ctrl-d> move ahead (down) half a screen • g move to the top of the file. • /text search forward for text • n repeat last search • q quit • b move back one full screen • k move back one line • <Ctrl-u> move back (up) half a screen • G move to the bottom of the file • ?text search backward for text • N repeat last search, but in opposite direction. • v open file in a text editor (vi by default)

42. less options • -c Clear before displaying. Screen is redrawn instead of scrolled between screens. • -r Display raw control characters. (May cause display problems) • -s “squeeze” multiple blank lines into a single blank line • -e Exit the second time it reaches the end of the line. • -m Verbose prompt, like more (by default it uses a colon).

43. Unit 4 • The bash Shell

44. bash introduction • “Bourne Again Shell” • Successor to sh, the original Unix shell • Developed for the GNU Project • The de factor standard Linux Shell • Backward-compatible with Bourne shell (sh)- the original (Standard) UNIX shell

45. bash Heritage and Features • Bourne Again Shell (bash) • Implements many of the best features from earlier shells: sh, csh, ksh , tcsh • Command line completion • Command line editing • Command line history • Sophisticated prompt control

46. Command Line Shortcuts:File Globbing • Globbing is wildcard expansion: • * - matches zero or more characters • ? – matches any single character • [a-z] – matches a range of characters • [^a-z] – matches all except the range. • The use of wildcards, or metacharacters, allows one pattern to expand to multiple filenames by a process called globbing. • RHEL uses UTF-8 encoding of characters, which means that each capital letter comes directly after the corresponding lower-case letter. • Use echo ?o* to find the effect of wild characters.

47. Some topics: Tab, history, ~ • The TAB Key • history • !! – to repeat last command • !c – to repeat last command that started with c • !n – to repeat a command by its number in history output • !?abc – to repeat last command that contains (as opposed to “started with”) abc • !-n – to repeat a command entered n commands back. • User ^old^new to repeat the last command with old changed to new. • Tilde(~) • May refer to your home directory ( ~/.bash_profile) • May refer to another user’s home directory. (~gmustafa/.bashrc)

48. Command Line Expansion:Variable and String • Parameter/Variable: ($) • Substitute the value of a variable in a command line. • $ cd $HOME/public/html • To see a list of variables and their values, run the set command. • Curly braces: { } • A string is created for every pattern inside the braces regardless if any file exists. • $ rm hello.{c,o} • Curly braces are useful for generating patterned strings.

49. Command Line Expansion:Command and Math • Command Output – ‘’ or $ () • Substitute output from a command in a command line. • $ echo “Hostname: `hostname`” • $ echo “Hostname: $(hostname)” • Arithmetic - $[] • Substitute result of arithmetic expression in a command line. • $echo Area : $[$X * $Y] • $echo Area : `expr $X\*$Y`

50. Protecting form Expansion:Backslash • Backslash (\) is the escape character and makes the next character literal. • $echo Your Cost :\$5.00 • Used as last character on line to “Continue command on next line” • $find / -name foo* • $find / -name foo\*