1. LINUX ADMINISTRATION 1

2. Unit 2 Chapter-1

3. CHAPTER 1 : RED HAT SYSTEM
Configuration Files
system configuration files in the /etc directory
The /etc directory is probably the most often visited directory
it is important to keep the file permissions set properly on everything in /etc
files such as /etc/shadow, where users‘ hashed
passwords are stored
The /etc/sysconfig directory contains configuration scripts

4. Examining the System Configuration Files.
Systemwide shell configuration scripts
These files determine the default environment settings of system shells
/etc/bashrc affects bash shells systemwide
but /home/siddhu/.bashrc effects only the shells started by user siddhu

5. SHELL CONFIG SCRIPTS: BASHRC, CSH.CSHRC, ZSHRC
Bashrc is read by bash,
csh.cshrc is read by tcsh
zshrc is read by zsh
PROFILE This file is read by all shells except
tcsh and csh upon login.
/etc/profile
System wide environment and startup programs
profile is a good place to set paths because it is where you set environmental variables
How many number of user commands saved in the .history
file in their home directory.
modify this line: HISTSIZE=1000
/etc/bashrc
Functions and aliases 5

6. BASH, TCSH, ZSH AND THEIR CONFIG FILE READ ORDERS
The shells read a couple different configuration files when starting up.
It is good to know which files are read in what order, so that you know where to set variables that will only apply to certain users.
bash files on startup:
/etc/profile,
~/.bash-->profile,
~/.bash-->login,
~/.profile. 1. 2. 3. 4.
Upon logout, bash reads
~/.bash-->logout. 1. 6

7. System environmental settings
MOTD
This file contains the message that users see every time they log in.
DIR-->COLORS
Red Hat Linux enables you to view file listings in color, as long as you are using a terminal program that supports colors.
executable files are green,
directories are dark blue,
symlinks are light blue,
regular files are white.
ISSUE.NET
Because it shows up to people who are connecting to your system over the Internet .
Messages displayed
Access is being monitored
Unauthorized access is prohibited 7

8. ALIASES
file /etc/mail/aliases is the aliases file for the sendmail program
The aliases file sends mail for all the basic system accounts such as bin, daemon, and operator, to root‘s mailbox
root: siddhu 8

9. DUMPDATES FSTAB LILO.CONF GRUB.CONF
If you do backups with dump, this file is important to you.
dumpdates stores information about the last system backup that was done.
FSTAB
fstab contains important information about your file
systems,
such as what file system type the partitions are, where they are located on the hard drive,
and what mount point is used to access them.
LILO.CONF
LILO is the boot time LInux LOader.
GRUB.CONF
grub stands for the modest acronym GRand Unified Bootloader. 9

10. CRON FILES
cron is a daemon that executes commands according to a preset schedule that a user defines.
User crontab files are stored in /var/spool/cron/.
cron files are stored in the following subdirectories of /etc directory
cron.d
cron.daily
cron.hourly
cron.monthly
cron.weekly
By default, a file in cron.d called sysstat runs a system activity accounting tool every 10 minutes, 24 x 7.

11. SYSLOG.CONF LD.SO.CONF LOGROTATE.CONF
The syslog daemon logs any notable events on your local system
It can store these logs in a local file or send them to a
remote log host for added security.
LD.SO.CONF
This configuration file is used by ldconfig. ldconfig configures dynamic linker runtime bindings.
It contains a listing of directories that hold shared
libraries.
Shared library files typically end with .so
static library files typically end with .a
LOGROTATE.CONF
logrotate can automatically rotate, compress, remove, and mail your log files
Log files can be rotated based on size or on time, such as daily, weekly, or monthly

12. System configuration files in the /etc/sysconfig directory
APMD
apmd contains configuration information for the advanced power management daemon
This is most useful for laptops rather than servers.
CLOCK
This file contains information on which time zone the machine is set to, and whether or not it is using Greenwich Mean Time for its system clock time.
AMD
amd is the file system automounter daemon.
It automatically mounts an unmounted file system whenever a file or directory within that file system is accessed.
UPS
make it easier for the Linux system to communicate with your UPS when the UPS needs to shut down the system. 12

13. EXAMINING THE NETWORK CONFIGURATION FILES
Files to change when setting up a system or
moving the system
files need to be modified to get it working on the new network
Set up the IP addresses of your network interfaces. Make changes to:
/etc/sysconfig/network-scripts/ifcfg-eth0
/etc/sysconfig/network-scripts/ifcfg-eth1
Set up the hostname of your machine. Make changes to:
/etc/sysconfig/network
/etc/hosts
Set up a default gateway. Make changes to:
/etc/default-route 13

14. Set up the DNS servers to reference. Make changes to:
/etc/resolv.conf
Make a local file of hostname to IP address mappings. Make changes to:
/etc/hosts
Set up the device order from which hostnames are looked up. Make changes to:
/etc/nsswitch.conf

15. SETTING UP THE IP ADDRESS
To set the IP address on your first Ethernet interface eth0,
edit the /etc/sysconfig/network-scripts/ifcfg-eth0 file.
 IPADDR=‛ ‛
 BROADCAST=
 NETMASK=‛ ‛

16. SETTING UP THE HOSTNAME
Once you‘ve picked your hostname, you need to put it into two different places:
/etc/sysconfig/network
/etc/hosts.
This is the /etc/sysconfig/network file:
NETWORKING=yes
HOSTNAME=‛siddhesh‛
 GATEWAY=‛ ‛
GATEWAYDEV=‛eth0‛
FORWARD_IPV4=‛yes‛
This is the /etc/hosts file
siddhesh localhost.localdomain

17. SETTING UP A DEFAULT GATEWAY
you need to tell it where to send all its traffic.
Ideally this would be a switch or a router that takes all your traffic in the direction of the Internet
/etc/default-route file to contain just the IP address of the gateway, like this: 

18. SETTING UP THE DNS SERVERS
Edit /etc/resolv.conf to contain a list of nameservers, like so:
nameserver
nameserver
nameserver

19. MAKING A LOCAL FILE OF HOSTNAME TO IP ADDRESS MAPPINGS
Your /etc/hosts file should contain IP address to
hostname mappings that follow this format:
IP_address canonical_hostname aliases
 sid.weit.net sid

20. Starting up network services from xinetd
xinetd is Red Hat 7.1‘s replacement for inetd.
xinetd is started on bootup
listens on ports designated in the /etc/xinetd.conf
for incoming network connections
When a new connection is made, xinetd starts up the corresponding network service

21. Starting up network services from the rc scripts
Network services that are not started out of xinetd
are started out of the rc scripts at boot time.

22. Network configuration files in the /etc/sysconfig directory
STATIC-ROUTES
Used to set up some static routes on your machine
IPTABLES
iptables is the next generation Linux firewall. It supercedes the ipchains firewall
IPCHAINS
ipchains is a Linux firewall that is now being superceded by iptables.
The GUI interface that configures the ipchains firewall
rules is firewall-config utility.
The ipchains rules are stored in the ipchains file.

23. Network configuration files in /etc/sysconfig/network-scripts
ifcfg-eth0 for your first Ethernet interface
IFUP AND IFDOWN
These files are symlinks to
/sbin/ifup and /sbin/ifdown.
call these scripts with the name of the interface that you want to bring up or down.
ifup eth0
ifdown eth0
Managing the init Scripts
The system boots into the default runlevel set in
/etc/inittab
File /etc/rc.d/rc.sysinit is an initialization file
Directories for particular runlevel /etc/rc.d/rc.0 to rc.6 23

24. Managing rc scripts using chkconfig
It helps the system administrator manage rc scripts and xinetd configuration files without having to manipulate them directly.
chkconfig
servicename
off|on|reset 24

25. THANK YOU 25