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Relational Database - Codd's Rules
Relational Database - Codd's Rules !!!A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd. Most popular commercial and open source databases currently in use are based on the relational database model.A short definition of an RDBMS may be a DBMS in which data is stored in the form of tables and the relationship among the data is also stored in the form of tables.
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">Codd's Rules- All database management must take place using the relational database's innate functionality
- All information in the database must be stored as values in a table
- All database information must be accessible through the combination of a table name, primary key and column name.
- The database must use NULL values to indicate missing or unknown information
- The database schema must be described using the relational database syntax
- The database may support multiple languages, but it must support at least one language that provides full database functionality (e.g. SQL)
- The system must be able to update all updatable views
- The database must provide single-operation insert, update and delete functionality
- Changes to the physical structure of the database must be transparent to applications and users.
- Changes to the logical structure of the database must be transparent to applications and users.
- The database must natively support integrity constraints.
- Changes to the distribution of the database (centralized vs. distributed) must be transparent to applications and users.
- Any languages supported by the database must not be able to subvert integrity controls.
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">Tags: database, table, DBMS, RDBMS, columns, Codd, E. F. Codd, rules, oracle, data================================================ O************************O***********************O
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Apt-Get command line tool
Apt-Get command line tool(Ubuntu's Advanced Packaging Tool) !!!
The apt-get command is a powerful command-line tool used to work with Ubuntu's Advanced Packaging Tool (APT) performing such functions as installation of new software packages, upgrade of existing software packages, updating of the package list index, and even upgrading the entire Ubuntu system.
*Install package
#sudo apt-get install packagename
*Remove Package
#sudo apt-get remove packagename
*Install Multiple Packages
#sudo apt-get install packagename1 packagename2 packagename3
*Update the Package Index
#sudo apt-get updateThe APT package index is essentially a database of available packages from the repositories defined in the /etc/apt/sources.list file.
*Upgrade the system
#sudo apt-get upgrade
*Read Debian APT User Manual
#sudo apt-get helpTags: apt get apt-get advanced packaging tool install remove upgrade update help ubuntu linux unix package-management
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Port Numbers - Linux
PORTS NUMBERS : Just as the physical address (MAC address) and the logical address (IP address) helps to route the traffic to a particular machine on a network, it is the port that identifies which service on the machine this traffic is destined to.
List of ports : /etc/servicesA port on a specific computer is called a socket. It can be open, closed, listening or have a connection established.
###Important PORT NUMBERS to remember:20 - FTP - data transfer21 - FTP - control (command)22 - SSH23 - Telnet25 - SMTP37 - Time43 - WHOIS42 - WINS53 - DNS67 - BOOTp68 - DHCP69 - TFTP79 - FINGER80 - HTTP (WWW)88 - Kerberose101 - HOSTNAME110 - POP3111 - rpcbind119 - NNTP123 - NTP (Time)137 - NetBios (nmbd)139 - NetBios ( Samba)143 - IMAP/Dovecot161 - SNMP180 - RIS220 - IMAP3389 - LDAP443 - HTTPs500 - Internet Key Exchange (IKE), IPSec520 - RIP546 - DHCPV6 client547 - DHCPV6 server554 - rtsp(Real Time Stream Protocol, Audio/Video)631 - Printing (ipp)744 - Flexlm901 - SWAT953 - rndc993 - IMAPSecure995 - POPs999 - POP over SSL/TLS2049 - NFS2082 - CPANEL2083 - CPANEL Secure SSL/TLS2086 - CPANEL WHM2087 - CPANEL WHM Secure/SSL2095 - CPANEL Webmail2096 - CPANEL Webmail Secure/SSL2222 - Direct Admin Control Panel2401 - CVSP server3268 - AD Global Catalog3269 - AD Global Catalog over SSL3306 - MySQL Server3389 - Terminal services (rdp-remote desktop protocol)4643 - Virtusso Power Panel(6000 - X116063)8443 - Pleask Control Panel9999 - Urchin10000- Webmin Control Panel21018- Skype
TAG: port, portnumber, port-numbers, tcp, udp, network, service, services, linux, socket, communication, transmission, dataflow, rhce, ubuntu, unix, red hat, red-hat, redhat
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How to install Webmin
WEBMINWebmin is a web-based interface for system administration for Unix. Using any modern web browser, you can setup user accounts, Apache, DNS, file sharing and much more. Webmin removes the need to manually edit Unix configuration files like /etc/passwd, and lets you manage a system from the console or remotely.
Install Webmin (Successfully tested/configured on Ubuntu server 10.04)
#sudo aptitude safe-upgrade
#sudo aptitude update
#sudo mkdir downloads
#cd downloads
#sudo wget http://downloads.sourceforge.net/project/webadmin/webmin/1.510/webmin_1.510-2_all.deb?use_mirror=cdnetworks-us-1
or
#sudo wget http://downloads.sourceforge.net/project/webadmin/webmin/1.510/webmin_1.510-2_all.deb?use_mirror=kent
#sudo dpkg -i webmin_1.510-2_all.deb
#sudo aptitude -f install=>>You can access the Ubuntu machine from a Windows machine via a web browser by typing the addresshttps://yourip:10000
or
https://core:10000 , here core is the name of my Ubuntu server.Tags: webmin web-based interface system administration admistrator configure linux server ubuntu red hat redhat rhel rhce unix
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How to break root password !!!
How to break root password !!!Method 1:1) When you reach the grub screen press 'e' on linux.2) Go to line which contains the word 'kernel' press 'e'3) go to the end of that line and write 'linux single' or '1'4) then press 'esc' twice and press 'b' to reboot the system5) now wait for the prompt and then type 'passwd root'6) enter new passwd1) Boot the computer with linux installation CD2) Enter the linux rescue mode by entering the following command in boot screenboot:linux rescue3) When the sh prompt is reached, enter the following commands to change root password:#chroot /mnt/sysimage#passwdThe above step will prompt you to enter your new password
Tags: rhel rhel5 rhce rhct hack how to break root password=================================================== O************************O***********************O
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Privacy Policy !!!
Privacy Policy for rhel5certs.blogspot.com/
If you require any more information or have any questions about our privacy policy, please feel free to contact us by email at rhcev5@gmail.com.
At rhel5certs.blogspot.com/, the privacy of our visitors is of extreme importance to us. This privacy policy document outlines the types of personal information is received and collected by rhel5certs.blogspot.com/ and how it is used.
Log Files
Like many other Web sites, rhel5certs.blogspot.com/ makes use of log files. The information inside the log files includes internet protocol ( IP ) addresses, type of browser, Internet Service Provider ( ISP ), date/time stamp, referring/exit pages, and number of clicks to analyze trends, administer the site, track user’s movement around the site, and gather demographic information. IP addresses, and other such information are not linked to any information that is personally identifiable.
Cookies and Web Beacons
rhel5certs.blogspot.com/ does not use cookies.
DoubleClick DART Cookie
.:: Google, as a third party vendor, uses cookies to serve ads on rhel5certs.blogspot.com/.
.:: Google's use of the DART cookie enables it to serve ads to users based on their visit to rhel5certs.blogspot.com/ and other sites on the Internet.
.:: Users may opt out of the use of the DART cookie by visiting the Google ad and content network privacy policy at the following URL - http://www.google.com/privacy_ads.html
Some of our advertising partners may use cookies and web beacons on our site. Our advertising partners include ....
These third-party ad servers or ad networks use technology to the advertisements and links that appear on rhel5certs.blogspot.com/ send directly to your browsers. They automatically receive your IP address when this occurs. Other technologies ( such as cookies, JavaScript, or Web Beacons ) may also be used by the third-party ad networks to measure the effectiveness of their advertisements and / or to personalize the advertising content that you see.
rhel5certs.blogspot.com/ has no access to or control over these cookies that are used by third-party advertisers.
You should consult the respective privacy policies of these third-party ad servers for more detailed information on their practices as well as for instructions about how to opt-out of certain practices. rhel5certs.blogspot.com/'s privacy policy does not apply to, and we cannot control the activities of, such other advertisers or web sites.
If you wish to disable cookies, you may do so through your individual browser options. More detailed information about cookie management with specific web browsers can be found at the browsers' respective websites.
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Disk Quotas
Disk space can be restricted by implementing disk quotas which alert a system administrator before a user consumes too much disk space or a partition becomes full. Disk quotas can be configured for individual users as well as user groups. This makes it possible to manage the space allocated for user-specific files (such as email) separately from the space allocated to the projects a user works on (assuming the projects are given their own groups).
In addition, quotas can be set not just to control the number of disk blocks consumed but to control the number of inodes (data structures that contain information about files in UNIX file systems). Because inodes are used to contain file-related information, this allows control over the number of files that can be created.
* Features of quotas
1). Limits disk usage (blocks or inodes)
2). Tied to file systems (et on a per file system basis)
3). can be configured for users and groups
* Steps to enable quota support :-
1) Enable quota support per file system in : /etc/fstab
a) defaults,usrquota,grpquota
Example:
#vi /etc/fstab
/dev/Volgroup00/logVol02/home ext3 defaults,usrquota,grpquota 1 2
2) Remount the file system(s)
a) mount -o remount /
b) use 'mount' to confirm that 'usrquota, grpquota' support are enabled
Example:
#mount -o remount /home
3) Create quota database files and generate disk usage table
a) quotacheck -mcug / (where c-create, u-user, g- group)
This creates /aquota.user and aquota.group
b) quotacheck -mavu
4) Assign quota policies:
a) edquota username (set blocks/inodes, soft_limits, hard_limits)
Example:
edquota student1 (sets quotas for user student1)
b) edquota -g devl
(for group quota, check using #quota -g devl)
5) Check quotas
#quota username
Example:
#quota student1
6) Report on usage
#repquota -a
==> The blocks are measured in 1K increments, eg 20000 blocks is roughly 20 MB.
* To change the grace period of quota
#edquota -t
* Managing quotas
If quotas are implemented, they need some maintenance-mostly in the form of watching to see if the quotas are exceeded and making sure the quotas are accurate.
a) Enabling and disabling quotas
i) To turn all user and group quotas off
#quotaoff -vuag
If neither the -u and -g options are specified, only the user quotas are disabled. If only -g is specified, only group quotas are disabled. The -v switches causes verbose status informtion to display as the command executes.
ii) To enable quotas again:
#quotaon -vaug
To enable quotas for a specific file system, such as /home, use the following
#quotaon -vug /home
If neither the -u or -g options are specified, only the user quotas are enabled. If only -g is specified, only group quotas are enabled.
b) Reporting on Disk Quotas
#repquota -a
c) Keeping Quotas accurate
Whenever a file system is not unmounted clearly (due to a system crash, for eg), it is necessary to run quotacheck. Running the following command periodically keeps the quotas more accurate.
#quotacheck -avug
The easiest way to run it periodically is to use cron.**********************************
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YUM - Yellowdog Updater, Modified
The Yellowdog Updater, Modified (YUM) is an open-source command-line package-management utility for RPM-compatible Linux operating systems and has been released under the GNU General Public License.
Copy/Backup the RHEL5 DVD on the local hdd.
Mount DVD drive:
#mount /dev/cdrom /media
Now copy all the files from the DVD disk to the local Hard disk drive
#mkdir /var/ftp/pub/rhel5
#cp -avf /dev/media/* /var/ftp/pub/rhel5
To configure YUM server, following rpm's and services are required:
1.vsftpd->vsftpd-2.0.5.10.el5.i386.rpm
a). Run vsftpd rpm
#rpm -ivh vsftpd-*.rpm
b). iptables -I INPUT -p tcp --dport 20 -j ACCEPT
iptables -I INPUT -p tcp --dport 21 -j ACCEPT
iptables -I INPUT -p udp --dport 21 -j ACCEPT
iptables -I INPUT -p udp --dport 20 -j ACCEPT
c). For SELinux
setsebool allow_ftpd_full_access on
d). open the file :- vim
#vim /etc/sysconfig/iptables-config and modify below mention line
IPTABLES_MODULES="ip_conntrack_netbios_ns ip_conntrack_ftp"
Now your ftp server is ready to take the responsibilty of yum server.
2.createrepo -> createrepo-0.4.11-3.el5.noarch.rpm
#cd /var/ftp/pub/rhel5/Server
#rpm -ivh createrepo-0.4.11-3.el5.noarch.rpm
#cd..
#createrepo -vg /var/ftp/pub/rhel5/Server/repodata/comps-rhel5-server-core.xml Server
*****ON CLIENT MACHINE*****
#vim /etc/yum.repos.d/rhel-debuginfo.repo
[reposfile]
name= Updates
baseurl=ftp://ipaddress/pub
enabled=1
gpgcheck=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
Eg: #vim /etc/yum.repos.d/client.repo
{*you can use the following lines if configuring on a local PC*}
[server]
name=YUM configuration for the client PC
baseurl=ftp://127.0.0.1/pub/rhel5/Server
gpgcheck=0
====>>>>press esc key and type ->:wq - to save the file and exit from vim*****************************************
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How To Pass RHCE Certification Exam
If you want to pass RHCE ( RED HAT CERTIFIED ENGINEER) certification exam, here are some useful tips for you::
1. There are 3 sections in RHCE exam.
a) First is the qualifying exam. If you clear this one, then only you can proceed for next section. If you fail to qualify, you wont get any certificate from Red Hat.
b) If you clear the qualification round, you are qualified for the second section. If you clear the second section too, you will atleast get a RHCT certificate.
NOTE: Even if you fail to clear the qualifying round, please do appear for the rest of the exam. Your won't get any certificate even if you score 100% in next two sections. But atlest you will get an idea about the format of the exam.
c) Those who clear the second round, are then eligible for the third section, and if they clear it, they become RHCE certified.
2. Remember its not an easy exam and if you will make a simple mistake that can fail you. So be very carefull. Its completely a practicle exam, so make a backup copy of every config file that you modify. So that if something goes wrong, you can copy the original file back into the same folder.
3. Books::
The books provided by Red Hat are very good. When you enroll for the examination, you get 3 books from Red Hat.
You can also study1) TATA McGRAW HILL's " RHCE Linux Study Guide" by Michael Jang2) SAMS " RHEL 5 Administration Unleashed "
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4. Install REDHAT ENTERPRISE LINUX 5.x (RHEL5.x) verison on your system.
You can also install VMWARE software and install a RHEL virtual machine on a Windows Terminal.
5. The only matra to pass this exam is " the more you practice, the more you learn ".
6. There are CBT Nuggets Videos tutorials also availabe. These videos are very helpfull. These videos teach you how to install and configure everything. Sometimes you find it lot more easier to learn from videos,rather than reading it from books. So follow whatever method suites you.
7. When you are appearing for the examination, do take one identification proof of yours like voter ID Card or a Driving license.
8. You are not allowed to take anything else in the examination room. So please do not take you vallet, books, mobile phones etc inside the examination lab.
9. While appearing for the qualifying round, make sure that you read the full instructions carefully. Please go through all the qualifying round questions first and then only start the exam. You are given one hour to solve the qualifying section. One thing very important to note here is that you can ask the examiner to check your machine ID and tell if your all the answers are correct. The examiner checks it from his terminal and informs you if you have any incorrect solution. You can then correct it and ask him again. If all your answers are correct he tells you that you have cleared the qualifying section and asks you to leave the room.
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10. You cannot discuss or publish the examination questions otherwise Red Hat can cancel your certificate.
Hope you will find the above tips helpfull and will regularly practice to clear this exam with flying colors. Best of Luck.
*** NOTE : I will also post more details about the format of this exam and the minimum marks required to clear the certification. Also post your comments and queries and I will try to reply back with solutions.
FOR MORE INFORMATION CLICK ON THIS LINK--->>> RED HAT WEBSITE
TAGS: rhce, redhat, red hat, redhat certified engineer, linux, rhel, rhel5, rhel5.x, red hat enterprise linux, rhce certification, red hat cert, fedora, unix, certiciation, certification exam
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