ITI481: Unix Administration

1
ITI-481 Unix Administration

• Meeting 2
• Rutgers University Center for Applied Computer
  Technologies
• Chris Uriarte, Instructor

2
Todays 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.

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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/ltDistri
  bution Namegt/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.

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RPM at the Command Line

• For a list of packages already installedrpm qa
• To install a new packagerpm ivh
  package-file-name
• To upgrade an existing packagerpm Uvh
  package-file-name
• To uninstall a package rpm e package-name
• (package name as seen in rpm qa)

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RPM at the Command Line (cont)

• List the files associated with a particular
  package
• rpm ql package-name

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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.

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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 CDgt cd
  /mnt/cdrom/Mandrake/RPMSgt rpm ivh
  tcpdump-3.6.1-1mdk.i586.rpm
• Uninstall elm software gt rpm -e elm-2.5.3-7mdk
• Question Is vim installed on your system? If
  so, what is the version number?

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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).

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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!

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Exercise Installing ssh1 from Source

• Download ssh1.2.27. Additional download
  locations can be found at http//www.ssh.com/produ
  cts/ssh/download.html.
• From the download directorygt tar -xvzf
  ssh-1.2.27.tar.gz gt cd ssh-1.2.27gt./configuregt
  makegt make install

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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

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Where to Find UNIX Software

• TwoCows http//www.twocows.com
• SunFreeware http//www.sunfreeware.com.
• Download.com http//www.download.com

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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/

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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)

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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.

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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, LILOs purpose is to identify the
  location of the kernel, which is actually just a
  file like/boot/vmlinuz-2.2.12-20

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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.

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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
  include0 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

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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

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UNIX Run Levels (cont)

• 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.

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UNIX Run Levels (cont)

• 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.

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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.

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rc Scripts

• Run level scripts are located in /etc/rc.d/rcX.d
  (Xrunlevel , 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.

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rc scripts, cont

• 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

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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.

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rc script diagram
/etc/rc.d/rc3.d
/etc/rc.d/rc5.d
/etc/rc.d/rc1.d
/etc/rc.d/rc2.d
S99checkwr
S99checkwr
S99checkwr
/etc/rc.d/init.d
Symbolic link
checkworldread
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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 ltrun levelgt (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.

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Changing the Default Run Level

• To change the default run level, edit
  /etc/inittab look for the line
• id3initdefault
• 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 youve
  specified otherwise during setup.

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Useful Keyboard Shortcuts

• Change to text consoleCTRL-ALT-F1-F6
• Change to X-Windows CTRL-ALT-F7
• Terminate X-Session CTRL-ALT-Backspace

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Exercise Changing Runlevels

• As root, type the followingshutdown 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, typeinit 5

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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.

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Homework

• Reading Linux Administration A Beginners Guide
  assigned in class.