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 Quick Revision Tips

Basic concepts like login and shell
a. The default shell is bash.
b. Do not set your default shell to ksh if you come from another UNIX. The test is geared towards bash.

Using the vi editor
a. Take time off to master the vi editor. It will prove useful during the test.

The Bourne Again Shell
a. The Bourne Again Shell is the default shell in Red Hat Linux. It is popularly known as "bash" .
b. Bash provides POSIX shell compatibilty, history, job control, command completion and many other features.
c. You can invoke command line completion by pressing the <TAB> key.

Processes
a. The default process priority is 0.
b. The lowest process priority is -19.
c. The highest process priority is 20.
d. You cannot renice a process downward and then renice it upward.

Standard I/O, Redirection and Piping
a. By default Linux commands expect their input to be text. Generally, they output text as well.
b. The 3 default filehandles available to any Linux process are stdin (0), stdout (1) and stderr (2).
c. By default the stdin is the keyboard, and the the stdout and stderr are both, the monitor.
d. The stdin, stdout and stderr, each can be reassigned to files.
Example :
foo < `cat data` 2> err 1> results
In this example, program foo accepts input from the command cat data, sends its output to the file results and all warnings and error messages to the file err.
e. The output of a command may also be sent to the stdin of another program. This is known as piping.
Example :
foo | sort
In this example the output of the comand foo is sent to the stdin of the command sort.

Using networking services
a. You can use ping to make sure that you can get onto the network.
b. You can use traceroute to find out whether you gateway configuration is correct.

Configuration of hardware
a. Make a habit of running lspci after every install.
b. For purposes of the test, you need not learn how to configure ISA devices.
c. If you have to change your NIC from brand A to brand B, then make sure that you have the driver in /lib/modules/<kernel-version>/drivers/ .
c. Look for a new PCI NIC in the listing of lspci and insmod its driver into a running kernel.

The Linux filesystem hierarchy
a. In general the Linux filesystem follows POSIX guidelines that specify that configuration info be kept separate from executables and further, that application data be separately maintained.
b. The configuration files are to be found in the /etc directory.
c. The log files are to be found in the /log directory.
d. The home directories of the users are in the /home directory.

Various types of installations
a. Never install using graphical mode. Always use text mode. It is much faster.
b. Practise network install as much as possible. Learn to install Red Hat over NFS, FTP and HTTP.
c. When given a choice, prefer an NFS install to an FTP install. Likewise prefer an FTP install to an HTTP install.
d. You will almost never have to install packages for text processing, databases ( like mysql or postgres ) and image processing. So don't.
e. Learn which application bundles are installed by default in a server.
f. You may generally skip making a bootdisk during installations.
g. Do install basic X. That way you can configure printing through the printtool.

Basic concepts like login and shell
a. The default shell is bash.
b. Do not set your default shell to ksh if you come from another UNIX. The test is geared towards bash. Its dumb. But thats the way it is.
c. The following manpages are important
i. cp
ii. ls
iii. rm
iv. chmod
v. passwd
vi. mkdir

The Bourne Again Shell
a. The Bourne Again Shell is the default shell in Red Hat Linux. It is popularly known as "bash" .
b. Bash provides POSIX shell compatibilty, history, job control, command completion and many other features.
c. You can invoke command line completion by pressing the <TAB> key.

Processes
a. The default process priority is 0.
b. The lowest process priority is -19.
c. The highest process priority is 20.
d. You cannot renice a process downward and then renice it upward.
e. The important manpages are
i. ps
ii. pstree
iii. nice
iv. renice
v. kill
vi. killall
vii. top

Standard I/O, Redirection and Piping
a. By default Linux commands expect their input to be text. Generally, they output text as well.
b. The 3 default filehandles available to any Linux process are stdin (0), stdout (1) and stderr (2).
c. By default the stdin is the keyboard, and the the stdout and stderr are both, the monitor.
d. The stdin, stdout and stderr, each can be reassigned to files. Example :
foo < `cat data` 2> err 1> results
In this example, program foo accepts input from the command cat data, sends its output to the file results and all warnings and error messages to the file err.
e. The output of a command may also be sent to the stdin of another program. This is known as piping.
Example :
foo | sort
In this example the output of the comand foo is sent to the stdin of the command sort.

Using networking services
a. You can use ping to make sure that you can get onto the network.
b. You can use traceroute to find out whether you gateway configuration is correct.

Configuration of hardware
a. Make a habit of running lspci after every install.
b. For purposes of the test, you need not learn how to configure ISA devices.
c. If you have to change your NIC from brand A to brand B, then make sure that you have the driver in /lib/modules/<kernel-version>/drivers/ .
d. In general, the native e100 driver by Intel works better than the default eepro series of drivers supplied with the Linux kernel. If you have a choice, use e100.
e. Look for a new PCI NIC in the listing of lspci and insmod its driver into a running kernel.
f. Important manpages are
i. proc
ii. lspci
iii. setpci
iv. setserial
v. fdisk
vi. mkfs
vii. mke2fs
viii. fsck
ix. e2fsck
x. hdparm
xi. mknod
xii. modemtool
xiii. sndconfig
xiv. dd

The Linux filesystem hierarchy
a. In general the Linux filesystem follows POSIX guidelines that specify that configuration info be kept separate from executables and further, that application data be separately maintained.
b. The configuration files are to be found in the /etc directory.
c. The log files are to be found in the /log directory.
d. The home directories of the users are in the /home directory.
e. The following manpages are important
i. df
ii. du

Utilities useful to system administrators
a. The cron suite is used for commands that have to be executred periodically.
b. The anacron command is used when it is not clear that the machine will be on at all times.
c. The find command is a versatile search utility to find files that match a variety of criteria.
d. Backups are made using the tar command.
e. The rpm command allows one to install, remove and query Red Hat packages.
f. The important manpages are
i. useradd
ii. find
iii. rsync
iv. rdist
v. rsh
vi. rcp
vii. rpm
viii. md5sum
ix. tar
x. cpio
xi. dump
xii. restore
xii. mt
xiii. usermod
xiv. userdel
xv. groupadd
xvi. groupmod
xv. groupdel
xvi. authconfig
xvii. chage
xviii. chown
xix. chgrp

Logging
a. The main system logger is the syslog whose log file is /var/log/messages . By default, programs like named log to this file.
b. The mail log is in /var/log/maillog .
c. The apache webserver logs to the /var/log/httpd/ directory. There are access_log and error_log files which log web traffic and errors if any.
d. The kernel boot messages are in /var/log/dmesg.
e. Learn the format of the following logfiles
i. syslog
ii. maillog
iii. xferlog
iv. All logs generated by apache - access_log and error_log

f. The following manpages are important
i. syslog
ii. syslog.conf

Configuring and troubleshooting X
a. Learn to use xf86config. It is old but still works just fine.
b. Learn to use Xconfigurator. It is standard in all distributions today.
c. Practise using the VGA mode. It is enough for most purposes including the test.
d. The following manpages are important
i. xfs
ii. xinitrc
iii.xauth
iv. X
v. xhost
vi. xdm
vii. gdm
viii. kdm

Basic networking
a. The configuration file for NIC eth0 is /etc/sysconfig/network-scripts/ifcfg-eth0. In this file you can set up the boot protocol, the IP address, the netmask and gateway for that interface.
b. You can allow a user to bring an interface up or down by setting the USERCTL directive in the init file of that interface
c. The following manpages are important
i. ifconfig
ii. netstat
iii. route
iv. ping
v. traceroute
vi. arpwatch
vii. arp

DNS
a. Bind 8 is the DNS server distributed with Red Hat.
b. Both master and slave servers provide authoratative information about a domain.
c. In case you have more than one nameserver in your /etc/resolv.conf file, the first available nameserver will be queried and the rest will be ignored. If the first available nameserver does not have information about the host, the host will be reported as unreachable.
d. The basic configuration file governing the behaviour of the nameserver is /etc/named.conf .
e. The first stanza in the named.conf is the "options" stanza. Read it carefully and make sure that you know which directory contains the zones for which this nameserver is authoritative.
f. If a hint file is provided, make sure that it exists.
g. When a query reaches a server, the server first checks its own cache, then it forwards it to the servers in its "hint" file.
h. When configuring a nameserver, make sure that the start of authority record is valid.
i. Red Hat recommends that the serial be in the format YYYYMMDDxx.
j. You may safely omit NS and MX records in the reverse lookup zone file.
k. Learn to use dig rather than nslookup.
l. Do not waste time learning about IPv6 or IPSec if the test is your objective.
m. The important manpages are
i. named
ii. named.conf
iii. resolv.conf
iv. resolver
v. nslookup
vi. dig
vii. host

Apache
a. To configure a virtualhost, you have to use the ServerName, ServerAdmin, DocumentRoot, ErrorLog and CustomLog directives. Enclose these in a VirtualHost container.
b. Set up the NameVirtualHost directive before the VirtualHost container.
c. To restrict access to a particular directory, you have to first set up a AllowOverride AuthConfig for that Directory in httpd.conf and later create a .htaccess file in that directory.
d. The following manpages are important
i. httpd
ii. htaccess
iii.htpasswd
iv. suexec

NIS
a. You can set the NIS domain of the host with the NISDOMAIN directive in /etc/sysconfig/network .
b. To set up an NIS server you need to install only the ypserv rpm.
c. Make sure that you are in runlevel 3 or above.
d. Make sure that both ypserv and yppasswdd are starting up in your runlevel if setting up an NIS server.
e. Check your NIS settings with rpcinfo -p localhost .
f. To set up an NIS client, you need to install the ypbind and yp-tools rpms.
g. Make sure that the NIS server's name is in /etc/yp.conf .
h. It is enough to place a the name of a directory in the /etc/exports file and run the command exportfs in order to share the directory on the network.
i. You need not learn much about LDAP for test preparation.
j. The following manpages are important.
i. showmount
ii. rpcinfo
iii. ypinit
iv. ypserv
v. ypbind
vi. exports
vii. auto.master
viii. portmap

Misc networking daemons such as ftpd
a. By default, all users are allowed to ftp into their home directories.
b. By default, anonymous access to /home/ftpd/pub directory is provided.
c. The important manpages are
i. ftpd
ii. wget
iii. ncftp
iv. pppd
v. chat
vi. wvdial
vii. ftpaccess
viii. xinetd
ix. dhcpd

Security and its aspects
a. Security has many aspects - user security, filesystem security, password security, and process security
b. Important manpages are
i. tripwire
ii. tmpwatch
iii. lsattr
iv. chattr
v. pam (concentrate on PAM)
vi. twintro
vii. twadmin
viii. twprint
ix. siggen
x. twconfig
xi. twpolicy
xii. twfiles
xiii. tcpdump
xiv. hosts.allow (Concentrate on TCP Wrappers)
xv. hosts.deny

Encrypted communications
a. The following commandline options of gpg are important -
gen-key, list-keys, list-secret-keys, export, import, armor, and recipient
b. The following manpages are important
i. ssh
ii. sshd
iii. openssh
iv. openssl
v. stunnel
vi. gpg
vii. ssh-keygen

Firewalls
a. There are 3 basic chains - input, output and forward.
b. If you have made any changes to the firewalling rules, they will be lost when you reboot. So service ipchains/iptables save chkconfig ipchains/iptables on service ipchains/iptables restart.
d. Important manpages are
i. iptables
ii. ipchains

Kernel compilation
a. Remember that Linux provides you with virtual terminals. Use them. Compile the kernel in one virtual terminal and do something else in another virtual terminal. Do not waste time staring at the screen while the kernel is compiling.
b. Always set EXTRAVERSION in the toplevel Makefile before doing anything else.
c. Use menuconfig if possible rather than xconfig.
d. If not using scsi, you may safely skip making a ramdisk.
e. Memorize the following line - make mrproper menuconfig dep bzImage modules modules_install .
f. Do not try to make modules modules_install in another virtual terminal. It might not work. This will waste more time.
g. Unless specifically instructed, cp -v the kernel to its location in the /boot. Unless so specifically instructed do not mv the kernel to its new location.
h. Remember to add a stanza to /etc/lilo.conf pointing to your new kernel. Do not modify existing stanzas unless you need to.
i. To reinstall lilo with your changes, use lilo -v -t first. This will run lilo in verbose test mode so that you know whether you have made any mistakes. If your lilo.conf is fine, install it with a lilo -v. You can never be too careful.
j. The important manpages are
i. lsmod
ii. insmod
iii. modprobe
iv. rmmod
v. modconf
vi. sysctl

Performance and tuning
a. If you are creating a filesystem for a database,
b. RAID5 is ideal but RAID0 works in most cases. Learn to mirror disks. Practise with IDE hard disks.
c. RAID5 makes for fast reads and slow writes.
d. There is a lot of documentation that comes with the raidtools package including a sample /etc/raidtab. Read the documentation carefully and experiment with RAID upto mirroring. No need to experiment beyond that.
Note : create RAID after installation, not during if not familiar.

Using Grep
To search a text file for a string of characters or a regular expression use grep as follows: 

grep pattern filename(s) 

Using this command you can check to see if a text file holds specific information. grep is often used to search the output from a command. 

The following are the most commonly used options of the grep command. 

-i Ignore the case of the letters when searching the file.

-n Output the line number of each line where a match is found in addition to      the line itself.

-v Output all the lines that DO NOT contain the search-string.

-w Output all the lines that contain the word being searched for.

Examples
a) Search for all the occurrences of the string able in the file Chapter1.txt. 
grep able Chapter1.txt 

b) Search for all the occurrences of the string able in the file Chapter1.txt, ignoring the case of the letters in making comparisons. 

grep -i able Chapter1.txt 

c) Search for all the occurrences of the string able in the file Chapter1.txt. Output the line number of each line where a match is found in addition to the line itself. 

grep -n able Chapter1.txt 

d) Output all the lines that DO NOT contain the string able in the file Chapter1.txt. 

grep -v able Chapter1.txt 

e) Output all the lines that contain the word able in the file Chapter1.txt. 

grep -w able Chapter1.txt 

f) Output all the lines that contain the string was able in the file Chapter1.txt. 

grep 'was able' Chapter1.txt 

g) All of the previous examples can be made applicable to a group of files by using the star convention. The following searches for the string able in all the files whose names start with Chapter. 

grep able Chapter* 

The string you are searching for can be more than one word (i.e. there is a space or other delimiter character such as a comma or a hyphen in the string). In such cases, single quotes (') may be placed around the string. It is also useful to know that the string is treated as a regular expression resulting in characters such as . and * having special meaning. 


grep copying help 

This searches the file help for the string copying and displays each line on your terminal. 

To search a file using regular expression: 

grep -n '[dD]on\'t' tasks 

This uses a regular expression to find and display each line in the file tasks that contains the pattern don't or Don't. The line number for each line is also displayed. The expression is quoted to prevent the shell expanding the metacharacters [, ] and '. Double quotes are used to quote the single quote in dDon't. 

To redirect the results of a search to a file: 

grep Smith /etc/passwd > smurffs 

This searches the passwd file for each occurrence of the name Smith and places the results of this search in the file smurffs. There being a lot of Smiths everywhere this is quite a large file. 


Using regular expressions with the grep command 
The following characters can be used to create regular expressions for searching on patterns with grep. Always quote the regular expression. This prevents the shell from interpreting the special characters before it is passed to the grep command. 


c any non-special character represents itself
\\c turns off the meaning of any special character
^ beginning of a line
$ end of a line
. matches any single character except a new line
[...] matches any of the enclosed characters
[^...] matches any character that is not enclosed
[n-n] matches any character in this range
* matches any number of the preceding character

Using vi Editor

To edit a file, just include the filename after it, e.g. vi filename. 
The escape key (<esc>) takes you out of insert mode and back to the command mode.
To siwtch to insert mode press i 
h move the cursor one character to the left 
j move the cursor one character down 
k move the cursor one character up 
l move the cursor one character to the right 
0 move to the beginning of a line 
$ move to the end of a line 
G move to the end of a file 
1G move to the first line of a file 
<ctrl-F> move down one screen 
<ctrl-B> move up one screen
x delete the character under the cursor 
dd delete a line

:w write to disk
ZZ write to disk and exit
:q! exit without writing to disk
dd deletes the current line of text and places it in a buffer.
yy copies the current line of text to a buffer while leaving the original text unaltered.

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