Transcript available here

ITI-481: Unix Administration
Meeting 2
Rutgers University Center for Applied Computer
Technologies
Chris Uriarte, Instructor
ITI-481 - Chris Uriarte
Today’s Agenda
• Software Installation
• Booting and Shutting Down
• Emergency Boot Procedures
ITI-481 - Chris Uriarte
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
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
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
RPM at the Command Line (con’t)
• List the files associated with a particular
package:
rpm –ql package-name
ITI-481 - Chris Uriarte
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-4.71i586.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. netscapecommunicator-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
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
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
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
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
Where to Find UNIX Software
• Tucows Linux
http://www.linuxberg.com
• Freshmeat
http://www.freshmeat.net/
• Rpmfind.net
http://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
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
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
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
The Linux Boot Process
1. LILO starts and Linux is selected as the
operating system to boot.
2. The Linux kernel is loaded into memory
and then probes system hardware.
3. The init process reads /etc/inittab
and determines whether runlevel 0-6
should be started.
4. rc scripts are executed for the specified
run level to start various services.
ITI-481 - Chris Uriarte
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
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
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
ITI-481 - Chris Uriarte
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
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
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
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
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
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
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
rc script diagram
/etc/rc.d/rc1.d
/etc/rc.d/rc2.d
/etc/rc.d/rc3.d
/etc/rc.d/rc5.d
S99checkwr
S99checkwr
S99checkwr
/etc/rc.d/init.d
Symbolic link
checkworldread
ITI-481 - Chris Uriarte
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 system
Can be disabled in /etc/inittab.
• ***Only power-cycle a UNIX system as a last resort.
ITI-481 - Chris Uriarte
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
Useful Keyboard Shortcuts
• Change to text console
CTRL-ALT-[F1-F6]
• Change to X-Windows
CTRL-ALT-F7
• Terminate X-Session
CTRL-ALT-Backspace
ITI-481 - Chris Uriarte
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
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
Homework
• Reading Linux Administration: A Beginner’s
Guide – assigned in class.
ITI-481 - Chris Uriarte