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ITI-481: Unix Administration

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  1. ITI-481: Unix Administration Meeting 2 Rutgers University Center for Applied Computer Technologies Chris Uriarte, Instructor ITI-481 - Chris Uriarte

  2. Today’s Agenda • Software Installation • Booting and Shutting Down • Emergency Boot Procedures ITI-481 - Chris Uriarte

  3. Software Installation • Methods of Installation • Binary distributions • Red Hat Package Manager (RPM) • Compiling from source • Software installations usually must be done as root. ITI-481 - Chris Uriarte

  4. Red Hat Package Manager (RPM) • Generally used for installation and removal of precompiled software. • Originally deployed on Linux systems, now available on other major platforms (most notably, Solaris) • Installation of operating system and additional software on many UNIX distributions managed through RPMs. • RPMs that are part of the Linux Distribution can be found on your install CD at:/mnt/cdrom/<Distribution Name>/RPMS • RPM installations are usually managed by the rpm command (/bin/rpm) • As close to “setup” as you can get on UNIX – one command installs an entire software package. ITI-481 - Chris Uriarte

  5. RPM at the Command Line • For a list of packages already installed:rpm –qa • To install a new package:rpm –ivh package-file-name • To upgrade an existing package:rpm –Uvh package-file-name • To uninstall a package: rpm –e package-name (package name as seen in “rpm –qa”) ITI-481 - Chris Uriarte

  6. RPM at the Command Line (con’t) • List the files associated with a particular package: rpm –ql package-name ITI-481 - Chris Uriarte

  7. Package Files vs. Installed Packages • An rpm package file is a file that contains all the software associated with a particular application. It ends with the .rpm extension, for example netscape-communicator-4.71-i586.rpm • When the package is installed, using the rpm –i option, the package name is officially entered in the system package database as the application name and version, i.e. netscape-communicator-4.71. Therefore, to remove the package, you need use the package name – not the full name of the file that you used to install the package. ITI-481 - Chris Uriarte

  8. Exercise: Using Red Hat Package Manager • Place your Linux CD in your drive - the files on your CD can now be accessed via the directory /mnt/cdrom. • The Mandrake/RPMS directory on your CDROM contains many RPM files. • Install tcpdump off of the Red Hat CD:> cd /mnt/cdrom/Mandrake/RPMS> rpm –ivh tcpdump-3.6.1-1mdk.i586.rpm • Uninstall elm software :> rpm -e elm-2.5.3-7mdk • Question: Is vim installed on your system? If so, what is the version number? ITI-481 - Chris Uriarte

  9. Installing Software from Source • A source installation takes raw computer code and compiles it into a usable software program. • Optimizes software for platform on which it is compiled. • Generally provides more installation and configuration options that using a binary or RPM distribution. • Requires a C compiler (gcc is the most common and is pre-installed with many systems). ITI-481 - Chris Uriarte

  10. Typical Steps for Installing from Source • Download source archive. • Unpack archive • filename.tar.gz or filename.tgz - use gzip and/or tar • filename.Z – use uncompress • filename.zip – use unzip • Look at README and/or INSTALL documents for specific installation steps. • Usually, you: • Run configure script if there is one. • Run make. • Run make install. • Key: READ the README and INSTALL files! ITI-481 - Chris Uriarte

  11. Exercise: Installing ssh1 from Source • Download ssh1.2.27. Additional download locations can be found at http://www.ssh.com/products/ssh/download.html. • From the download directory:> tar -xvzf ssh-1.2.27.tar.gz > cd ssh-1.2.27>./configure> make> make install ITI-481 - Chris Uriarte

  12. Where to Find UNIX Software • Tucows Linuxhttp://www.linuxberg.com • Freshmeathttp://www.freshmeat.net/ • Rpmfind.nethttp://rpmfind.net/linux/RPM/ • Updates for packages distributed with Red Hat Linux can be found at any of the Red Hat Mirrors: http://www.redhat.com/download/mirror.html ITI-481 - Chris Uriarte

  13. Where to Find UNIX Software • TwoCows – http://www.twocows.com • SunFreeware – http://www.sunfreeware.com. • Download.com – http://www.download.com ITI-481 - Chris Uriarte

  14. When will you use these software installation procedures? • When you want to install a new system or user application. • When you need to apply patches, fixes or updates that have been provided by your OS vendor. • i.e. RedHat security patches and bug fixes available at: http://www.redhat.com/apps/support/errata/ ITI-481 - Chris Uriarte

  15. The UNIX Boot Process • The UNIX boot process is unique. • UNIX is divided into system states called “run levels”, ranging from level 0 to level 6. • UNIX Flavors boot differently, but the general concepts are always the same: • Bootstrap the system using a bootloader • Load the “kernel” into memory • Execute “rc scripts” (startup scripts) ITI-481 - Chris Uriarte

  16. The Linux Boot Process • LILO starts and Linux is selected as the operating system to boot. • The Linux kernel is loaded into memory and then probes system hardware. • The init process reads /etc/inittab and determines whether runlevel 0-6 should be started. • rc scripts are executed for the specified run level to start various services. ITI-481 - Chris Uriarte

  17. Linux Loader (LILO) • LILO is a boot manager. • Usually installed in the Master Boot Record (MBR – a special segment of your hard disk that the system reads during startup). • Configuration file is /etc/lilo.conf. If any changes are made to lilo.conf, /sbin/lilo needs to be run for the changes to become active. • For Linux, LILO’s purpose is to identify the location of the kernel, which is actually just a file like:/boot/vmlinuz-2.2.12-20 ITI-481 - Chris Uriarte

  18. General UNIX System Booting • Linux is unique, as it uses LILO - a very interactive bootloading system. • Administrators rarely interact with the bootloader on other flavors of UNIX (unless a special bootloader is present). • Other UNIX flavors, however, have capabilities that are similar to those of LILO. ITI-481 - Chris Uriarte

  19. The UNIX init Process • init reads /etc/inittab, which designates what runlevel to start. A runlevel of initdefault is selected unless otherwise designated. • A runlevel determines what functionality the system should be providing. Run levels include:0 Halt the system1 Single-user (no networking)2 Multiuser without NFS3 Multiuser with NFS4 Unused5 Same as 3 but with X11 console6 Reboot the system ITI-481 - Chris Uriarte

  20. UNIX Run Levels • Run Level 1 – “single user mode” • No prompts for username/password • Access only via console – no remote access to the system (i.e. telnet) • Very minimal services are running – no networking, no X Windows. • Console user has “root” permissions • User for system maintenance • Used when you forget your root password ITI-481 - Chris Uriarte

  21. UNIX Run Levels (con’t) • Run Level 2 • All typical services are started • Multi-user mode – users are allowed to log into the system • NO NFS (Network File System) file sharing • Run Level 3 • Same as run level 2, but NFS is enabled. • ***This is the DEFAULT system run level. ITI-481 - Chris Uriarte

  22. UNIX Run Levels (con’t) • Run Level 4 • Not used (historical) • Run Level 5 • Same as run level 3, but the system will automatically boot into X Windows and console users will authenticate via an X Windows username/password interface. ITI-481 - Chris Uriarte

  23. Special Run Levels • Run Level 0 • The system “halt” or “shutdown” run level • System processes are stopped and the system halts • Run Level 6 • The system “reboot” run level. • System processes are stopped and the machine is restarted. ITI-481 - Chris Uriarte

  24. rc Scripts • Run level scripts are located in /etc/rc.d/rcX.d (X=runlevel #, e.g. /etc/rc.d/rc3.d for run level 3). They are used for both startup and shutdown purposes. • These directories have startup scripts that run processes and applications during boot time. The scripts use the following naming convention: • K or S + Number + Service Name (i.e. S80sendmail) • S is for start. K is for kill. Lower numbers start before higher. • Startup scripts take two options: start or stop. Scripts with a S are run with start option. Scripts with a K are run with a stop option. ITI-481 - Chris Uriarte

  25. rc scripts, con’t • The scripts in the rcX.d directories are typically NOT actual files themselves – they are usually symbolic links to links to scripts located in /etc/rc.d/init.d or /etc/init.d • For example: • A script that starts the apache server, might exist: /etc/rc.d/init.d/apache. This script need only contain the commands that required to start apache. • To start Apache during run level 3, create a symbolic link in /etc/rc.d/rc3.d called, for example, S99apache and link it to /etc/rc.d/init.d/apache ITI-481 - Chris Uriarte

  26. rc script example • Example – you create a script that checks the system for “world writeable” files (files that anyone on the system can write to) and emails these files to you. • This script is called checkworldread and is located in /etc/rc.d/init.d. • You would like to run this script when the system starts in ANY multiuser mode (I.e. run level 2, 3 and 5) • Therefore, you must create rc-style symbolic links to /etc/rc.d/init.d/checkworldread from the /etc/rc.d/rc2.d, rc3.d and rc5.d directories. ITI-481 - Chris Uriarte

  27. rc script diagram /etc/rc.d/rc1.d /etc/rc.d/rc3.d /etc/rc.d/rc5.d /etc/rc.d/rc2.d S99checkwr S99checkwr S99checkwr /etc/rc.d/init.d Symbolic link checkworldread ITI-481 - Chris Uriarte

  28. Ways of Changing Run Levels • /sbin/telinit [0-6] or /sbin/init [0-6] • Allows you to specify a specific run level to change to • /sbin/shutdown (typically, “shutdown now”) • /sbin/reboot • /sbin/halt • At LILO boot prompt type linux <run level> (i.e. ‘linux 5’) • CTRL-ALT-DELETE • Key combination on PC-based UNIX systems reboots the systemCan be disabled in /etc/inittab. • ***Only power-cycle a UNIX system as a last resort. ITI-481 - Chris Uriarte

  29. Changing the Default Run Level • To change the default run level, edit /etc/inittab – look for the line: id:3:initdefault: • After “id:” put the run level number you wish to use as your default run level. (usually 3 and 5 are most common options) • Now when your machine boots, it will automatically enter that run level. • The default UNIX run level is 3, unless you’ve specified otherwise during setup. ITI-481 - Chris Uriarte

  30. Useful Keyboard Shortcuts • Change to text consoleCTRL-ALT-[F1-F6] • Change to X-Windows CTRL-ALT-F7 • Terminate X-Session CTRL-ALT-Backspace ITI-481 - Chris Uriarte

  31. Exercise: Changing Runlevels • As root, type the following:shutdown –t 30 –h “System Downtime Beginning” • Hit the power switch on your machine to turn the system back on after the shutdown process is complete. NEVER turn power off without a proper shutdown. • At the LILO prompt, enter “linux 1.” (Linux only) • After booting into single-user mode, type:init 5 ITI-481 - Chris Uriarte

  32. Emergency Boot Procedures • If system is unable to boot normally or you forgot your root password, the following options are available: • Boot off of your system-specific boot disk – • Can be created usually be created during a UNIX install process. Linux also has a “mkbootdisk” command. • Boot off of your install floppy or cdrom. You may be prompted to boot into single user mode or into a “recovery mode” • Boot into single user mode. ITI-481 - Chris Uriarte

  33. Homework • Reading Linux Administration: A Beginner’s Guide – assigned in class. ITI-481 - Chris Uriarte