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Unix Administration 2


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  • Verify the version number of tcpdump and elm for Mandrake 8.0 Check to make sure vim is actually a package on the system
  • Verify that the SSH link runs Maybe there’s a better piece of software to run?
  • 1. Maybe put in a link to some security/patch pages.
  • 1. Check Kernel version and update
  • Transcript

    • 1. ITI-481: Unix Administration Meeting 2 Rutgers University Center for Applied Computer Technologies Chris Uriarte, Instructor
    • 2. Today’s Agenda
      • Software Installation
      • Booting and Shutting Down
      • Emergency Boot Procedures
    • 3. Software Installation
      • Methods of Installation
        • Binary distributions
        • Red Hat Package Manager (RPM)
        • Compiling from source
      • Software installations usually must be done as root.
    • 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.
    • 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”)
    • 6. RPM at the Command Line (con’t)
      • List the files associated with a particular package:
        • rpm –ql package-name
    • 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.
    • 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?
    • 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).
    • 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
        • – 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!
    • 11. Exercise: Installing ssh1 from Source
      • Download ssh1.2.27 . Additional download locations can be found at .
      • From the download directory: > tar -xvzf ssh-1.2.27.tar.gz > cd ssh-1.2.27 >./configure > make > make install
    • 12. Where to Find UNIX Software
      • Tucows Linux
      • Freshmeat
      • 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
    • 13. Where to Find UNIX Software
      • TwoCows –
      • SunFreeware – .
      • –
    • 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/
    • 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)
    • 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.
    • 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
    • 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.
    • 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 system 1 Single-user (no networking) 2 Multiuser without NFS 3 Multiuser with NFS 4 Unused 5 Same as 3 but with X11 console 6 Reboot the system
    • 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
    • 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.
    • 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.
    • 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.
    • 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.
    • 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
    • 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.
    • 27. rc script diagram /etc/rc.d/rc2.d /etc/rc.d/rc3.d /etc/rc.d/rc5.d /etc/rc.d/rc1.d S99checkwr S99checkwr S99checkwr /etc/rc.d/init.d checkworldread Symbolic link
    • 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’)
        • Key combination on PC-based UNIX systems reboots the system Can be disabled in /etc/inittab.
      • ***Only power-cycle a UNIX system as a last resort.
    • 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.
    • 30. Useful Keyboard Shortcuts
      • Change to text console CTRL-ALT-[F1-F6]
      • Change to X-Windows CTRL-ALT-F7
      • Terminate X-Session CTRL-ALT-Backspace
    • 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
    • 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.
    • 33. Homework
      • Reading Linux Administration: A Beginner’s Guide – assigned in class.