Archive for category Red hat Linux tips
Critical to a Linux administrator is knowledge of one or more text editors to manage the many configuration files on a Linux system. The Linux file system hierarchy organizes hardware, drivers, directories, and of course, files. You need to master a number of basic commands to manage Linux. Printer configuration can be a complex topic. Shell scripts enable you to automate many everyday processes. Security is now a huge issue that Linux can handle better than other operating systems; locally, and on larger networks such as the Internet.
The VIsual Editor
Linux and Unix are managed through a series of text files. Linux administrators do not normally use graphical editors to manage these configuration files. Editors such as WordPerfect, starOffice, and yes, even Microsoft Word normally save files in a binary format that Linux can’t read. Popular text editors for Linux configuration files include emacs, pico, joe, and vi.
While emacs may be the most popular text editor in the world of Linux, every administrator needs at least a basic knowledge of vi. While emacs may be more popular and flexible, vi may help you save a broken system. If you ever have to restore a critical configuration file using an emergency boot floppy, vi is probably the only editor that you’ll have available. You need to know how to restore your system from a rescue floppy, which does not have enough room to carry any editor other than vi.So should know how to use vi editor.
$ vi /tmp/test
If this is a new file, you should see something similar to the following:
“/tmp/test” [New File]
The box at the top represents where your cursor is. The bottom line keeps you informed about what is going on with your editing (here you just opened a new file). In between, there are tildes (~) as filler because there is no text in the file yet. Now here’s the intimidating part: There are no hints, menus, or icons to tell you what to do. On top of that, you can’t just start typing. If you do, the computer is likely to beep at you. And some people complain that Linux isn’t friendly.
The first things you need to know are the different operating modes: command and input. The vi editor always starts in command mode. Before you can add or change text in the file, you have to type a command (one or two letters and an optional number) to tell vi what you want to do. Case is important, so use uppercase and lowercase exactly as shown in the examples! To get into input mode, type an input command. To start out, type either of the following:
a-The add command. After it, you can input text that starts to the right of the cursor.
i-The insert command. After it, you can input text that starts to the left of the cursor.
Type a few words and then press Enter. Repeat that a few times until you have a few lines of text. When you’re finished typing, press Esc to return to command mode. Now that you have a file with some text in it, try moving around in your text with the following keys or letters: Remember the Esc key! It always places you back into command mode.
Arrow keys-Move the cursor up, down, left, or right in the file one character at a time. To move left and right you can also use Backspace and the space bar, respectively. If you prefer to keep your fingers on the keyboard, move the cursor with h (left), l (right), j (down), or k (up).
w-Moves the cursor to the beginning of the next word.
b-Moves the cursor to the beginning of the previous word.
0 (zero)-Moves the cursor to the beginning of the current line.
$-Moves the cursor to the end of the current line.
H-Moves the cursor to the upper-left corner of the screen (first line on the screen).
M-Moves the cursor to the first character of the middle line on the screen.
L-Moves the cursor to the lower-left corner of the screen (last line on the screen).
The only other editing you need to know is how to delete text. Here are few vi commands for deleting text:
x-Deletes the character under the cursor.
X-Deletes the character directly before the cursor.
dw-Deletes from the current character to the end of the current word.
d$-Deletes from the current character to the end of the current line.
d0-Deletes from the previous character to the beginning of the current line.
To wrap things up, use the following keystrokes for saving and quitting the file:
ZZ-Save the current changes to the file and exit from vi.
:w-Save the current file but continue editing.
:wq-Same as ZZ.
:q-Quit the current file. This works only if you don’t have any unsaved changes.
:q!-Quit the current file and don’t save the changes you just made to the file.
If you’ve really trashed the file by mistake, the :q! command is the best way to exit and abandon your changes.
The file reverts to the most recently changed version. So, if you just did a :w, you are stuck with the changes up to that point. If you just want to undo a few bad edits, press u to back out of changes.
You have learned a few vi editing commands. I describe more commands in the following sections. First, however,
here are a few tips to smooth out your first trials with vi:
Esc-Remember that Esc gets you back to command mode. (I’ve watched people press every key on the keyboard trying to get out of a file.) Esc followed by ZZ gets you out of command mode, saves the file, and exits.
u-Press u to undo the previous change you made. Continue to press u to undo the change before that, and the one before that.
Ctrl+R-If you decide you didn’t want to undo the previous command, use Ctrl+R for Redo. Essentially, this command undoes your undo.
Caps Lock-Beware of hitting Caps Lock by mistake. Everything you type in vi has a different meaning when the letters are capitalized. You don’t get a warning that you are typing capitals-things just start acting weird.
:! command-You can run a command while you are in vi using :! followed by a command name. For example,
type :!date to see the current date and time,
type :!pwd to see what your current directory is,
type :!jobs to see if you have any jobs running in the background.
INSERT-When you are in insert mode, the word INSERT appears at the bottom of the screen.
Ctrl+G-If you forget what you are editing, pressing these keys displays the name of the file that you are editing and the current line that you are on at the bottom of the screen. It also displays the total number of lines in the file, the percentage of how far you are through the file, and the column number the cursor is on.
Moving Around the File
Besides the few movement commands described earlier, there are other ways of moving around a vi file. To try these out, open a large file that you can’t do much damage to. (Try copying /var/log/ messages to /tmp and opening it in vi.) Here are some movement commands you can use:
Ctrl+F-Page ahead, one page at a time.
Ctrl+B-Page back, one page at a time.
Ctrl+D-Page ahead one-half page at a time.
Ctrl+U-Page back one-half page at a time.
G-Goto the last line of the file.
1G-Go to the first line of the file. (Use any number to go to that line in the file.)
Searching for Text
To search for the next occurrence of text in the file, use either the slash (/) or the question mark (?) character. Follow the slash or question mark with a pattern (string of text) to search forward or backward, respectively, for that pattern. Within the search, you can also use metacharacters. Here are some examples:
/hello-Searches forward for the word hello.
?goodbye-Searches backward for the word goodbye.
/The.*foot-Searches forward for a line that has the word The in it and also, after that at some point, the word foot.
?[pP]rint-Searches backward for either print or Print. Remember that case matters in Linux, so make use of brackets to search for words that could have different capitalization.
The vi editor was originally based on the ex editor, which didn’t let you work in full-screen mode. However, it did enable you to run commands that let you find and change text on one or more lines at a time. When you type a colon and the cursor goes to the bottom of the screen, you are essentially in ex mode. Here is an example of some of those ex commands for searching for and changing text. (I chose the words Local and Remote to search for, but you can use any appropriate words.)
:g/Local-Searches for the word Local and prints every occurrence of that line from the file. (If there is more than a screenful, the output is piped to the more command.)
:s/Local/Remote-Substitutes Remote for the word Local on the current line.
:g/Local/s//Remote-Substitutes the first occurrence of the word Local on every line of the file with the word Remote.
:g/Local/s//Remote/g-Substitutes every occurrence of the word Local with the word Remote in the entire file.
:g/Local/s//Remote/gp-Substitutes every occurrence of the word Local with the word Remote in the entire file, and then prints each line so that you can see the changes (piping it through more if output fills more than one page).
Using Numbers with Commands
You can precede most vi commands with numbers to have the command repeated that number of times. This is a handy way to deal with several lines, words, or characters at a time. Here are some examples:
3dw-Deletes the next three words.
5cl-Changes the next five letters (that is, removes the letters and enters input mode).
12j-Moves down 12 lines.
Putting a number in front of most commands just repeats those commands. At this point, you should be fairly proficient at using the vi command. Once you get used to using vi, you will probably find other text editors less efficient to use.
Everything in Linux can be reduced to a file. Partitions are associated with files such as /dev/hda1. Hardware components are associated with files such as /dev/modem. Detected devices are documented as files in the /proc directory. The Filesystem Hierarchy Standard (FHS) is the official way to organize files in Unix and Linux directories.
Linux/Unix Filesystems and Directories
Several major directories are associated with all modern Unix/Linux operating systems. These directories organize user files, drivers, kernels, logs, programs, utilities, and more into different categories. The standardization of the FHS makes it easier for users of other Unix-based operating systems to understand the basics of Linux. Every FHS starts with the root directory, also known by its label, the single forward slash (/). All of the other directories shown in Table are subdirectories of the root directory. Unless they are mounted separately, you can also find their files on the same partition as the root directory.
/ The root directory, the top-level directory in the FHS. All other directories are subdirectories of root, which is always mounted on some partition. All directories that are not mounted on a separate partition are included in the root directory’s partition.
/bin Essential command line utilities. Should not be mounted separately; otherwise, it could be difficult to get to these utilities when using a rescue disk.
/boot Includes Linux startup files, including the Linux kernel. Can be small; 16MB is usually adequate for a typical modular kernel. If you use multiple kernels, such as for testing a kernel upgrade, increase the size of this partition accordingly.
/etc Most basic configuration files.
/dev Hardware and software device drivers for everything from floppy drives to terminals. Do not mount this directory on a separate partition.
/home Home directories for almost every user.
/lib Program libraries for the kernel and various command line utilities. Do not mount this directory on a separate partition.
/mnt The mount point for removable media, including floppy drives, CD-ROMs, and Zip disks.
/opt Applications such as WordPerfect or StarOffice.
/proc Currently running kernel-related processes, including device assignments such as IRQ ports, I/O addresses, and DMA channels.
/root The home directory of the root user.
/sbin System administration commands. Don’t mount this directory separately.
/tmp Temporary files. By default, Red Hat Linux deletes all files in this directory periodically.
/usr Small programs accessible to all users. Includes many system administration commands and utilities.
/var Variable data, including log files and printer spools.
Types of Files Used by Linux
When working with Linux, you need to be aware of the fact that there are a number of different file types used by the file system. This is another area where the Linux file system differs significantly from the Windows file system. With a Windows file system you basically have two entry types in the file system:
Granted, you can have normal files, hidden files, shortcut files, word processing files, executable files, and so on. However, these are all simple variations of the basic file when working with Windows.
With Linux, however, there are a variety of different file types used by the file system. These include the file types shown in Table
File Type Description
Regular files These files are similar to those used by the file systems of other operating systems—for example, executable files, OpenOffice.org files, images, text configuration files, etc.
Links These files are pointers that point to other files in the file system.
FIFOs FIFO stands for First In First Out. These are special files used to move data from one running process on the system to another. A FIFO file is basically a queue where the first chunk of data added to the queue is the first chunk of data removed from the queue. Data can only move in one direction through a FIFO.
Sockets Sockets are similar to FIFOs in that they are used to transfer information between sockets. With a socket, however, data can move bi-directionally.
Some of the Configuration Files in /etc Directory that you should remember
/etc/fstab Lists the partitions and file systems that will be automatically mounted when the system boots.
/etc/group Contains local group definitions.
/etc/grub.conf Contains configuration parameters for the GRUB bootloader (assuming it’s being used on the system).
/etc/hosts Contains a list of hostname-to-IP address mappings the system can use to resolve hostnames.
/etc/inittab Contains configuration parameters for the init process.
/etc/init.d/ A subdirectory that contains startup scripts for services installed on the system. On a Fedora or Red Hat system, these are located in /etc/rc.d/init.d.
/etc/modules.conf Contains configuration parameters for your kernel modules.
/etc/passwd Contains your system user accounts.
/etc/shadow Contains encrypted passwords for your user accounts.
/etc/X11/ Contains configuration files for X Windows.
Study Points for the RHCE Exam
use standard command line tools (e.g., ls, cp, mv, rm, tail, cat, etc.) to create, remove, view, and investigate files and directories
use grep, sed, and awk to process text streams and files
use a terminal-based text editor, such as vim or nano, to modify text files
use input/output redirection
understand basic principles of TCP/IP networking, including IP addresses, netmasks, and gateways for IPv4 and IPv6
use su to switch user accounts
use passwd to set passwords
use tar, gzip, and bzip2
configure an email client on Red Hat Enterprise Linux
use text and/or graphical browser to access HTTP/HTTPS URLs
use lftp to access FTP URLs
Troubleshooting and System Maintenance
RHCTs should be able to:
boot systems into different run levels for troubleshooting and system maintenance
diagnose and correct misconfigured networking
diagnose and correct hostname resolution problems
configure the X Window System and a desktop environment
add new partitions, filesystems, and swap to existing systems
use standard command-line tools to analyze problems and configure system
Installation and Configuration
RHCTs must be able to:
perform network OS installation
implement a custom partitioning scheme
configure the scheduling of tasks using cron and at
attach system to a network directory service, such as NIS or LDAP
add and manage users, groups, quotas, and File Access Control Lists
configure filesystem permissions for collaboration
install and update packages using rpm
properly update the kernel package
configure the system to update/install packages from remote repositories using yum or pup
modify the system bootloader
implement software RAID at install-time and run-time
use /proc/sys and sysctl to modify and set kernel run-time parameters
use scripting to automate system maintenance tasks
configure NTP for time synchronization with a higher-stratum server
Troubleshooting and System Maintenance
RHCEs must demonstrate the RHCT skills listed above, and should be able to:
use the rescue environment provided by first installation CD
diagnose and correct boot failures arising from bootloader, module, and filesystem errors
diagnose and correct problems with network services (see Installation and Configuration below for a list of these services)
add, remove, and resize logical volumes
diagnose and correct networking services problems where SELinux contexts are interfering with proper operation.
Installation and Configuration
RHCEs must demonstrate the RHCT-level skills listed above, and they must be capable of configuring the following network services:
IMAP, IMAPS, and POP3
DNS (caching name server, slave name server)
For each of these services, RHCEs must be able to:
install the packages needed to provide the service
configure SELinux to support the service
configure the service to start when the system is booted
configure the service for basic operation
Configure host-based and user-based security for the service
RHCEs must also be able to:
configure hands-free installation using Kickstart
implement logical volumes at install-time
use iptables to implement packet filtering and/or NAT
use PAM to implement user-level restrictions
Based on this RHCE guide we have created step by step guide of RHCE exam. By our RHCE guide you can get your RHCE certificates. We have managed various practical example and suggest you to go through all these.
RHCE exam assesses the candidates ability to do the following:
1-Install and configure Red Hat Linux
2-Configure file systems and networking
3-Configure X, the graphical user interface used on Unix and Linux systems
4-Configure basic security
5-Configure network services
6-Perform routine maintenance
7-Perform diagnostics and troubleshooting
Because Red Hat regularly updates its Linux distribution, RHCE certification is not valid indefinitely. However, according to Red Hat policy, RHCE certification remains valid for at least one year.
RHCE Courses and Exam
as part of its RHCE program, Red Hat offers several courses designed to prepare candidates for the RHCE exam. Candidates must take course RH302, which is the exam itself. However, candidates can take none, some, or all of the other courses.
This section describes the RHCE courses offered by Red Hat, as well as the RH302 exam.
RH033: Introduction to Red Hat Linux I, II
RH033 is a four-day course intended for users who have no previous Unix or Linux experience. Students should, however, have previous experience with a computer, including use of a mouse and graphical user interface. Upon completion of the course, the student should be able to use and customize the GNOME desktop and be able to use the Linux command shell.
RH133: Red Hat Linux System Admin I, II
RH133 is a four-day course intended for users who are familiar with Red Hat Linux. Before taking this course, students should complete RH033 or possess equivalent experience. Upon completion of the course, students should be able to install and configure Red Hat Linux, X, and various network services and clients, such as DHCP, NIS, NFS, and Samba. Students should also be able to perform basic troubleshooting and rebuild the Linux kernel from source code.
RH253: Red Hat Linux Networking and Security Admin
RH253 is a four-day course intended for Unix or Linux system administrators. Before taking this course, students should complete RH133 or possess equivalent experience. Upon completion of the course, students should be able to install and configure network services such as Apache, DHCP, DNS, FTP, Samba, NFS, sendmail, and IMAP4/POP3 mail. Students should also be able to establish and administor a security policy that includes such elements as password security, kernel security, public/private key encryption, Kerberos, secure shell, and firewalls.
RH300 is a five-day course that includes RH302, the RHCE exam, as an integral part of the course. Before taking this course, students should complete RH253 or possess equivalent experience and have experience as a Unix or Linux system or network administrator. The course consists of four days of instruction, and the fifth day is devoted to the RHCE exam. Upon completion of the course, students should be prepared to manage a Red Hat Linux system that offers common TCP/IP services, such as FTP and HTTP. The course includes eight units of instruction, each of which has one or more hands-on labs associated with the following topics:
Hardware and Installation (x86 Architecture)
Configuration and Administration
Alternate Installation Methods
Kernel Services and Configuration
Standard Networking Services
X Window System
User and Host Security
Routers, Firewalls, Clusters, and Troubleshooting
RH302: RHCE Exam
Though styled by Red Hat as a course, RH302 is not a course in the ordinary sense of the word. Instead, RH302 is the RHCE exam, which has duration of one day. RH302 is the only course that RHCE candidates must take. The exam consists of the following three closed-book components:
Diagnosis and troubleshooting lab (2 1/2 hours)
Installation and configuration lab (2 1/2 hours)
Multiple choice exam (1 hour)
Effective May 1, 2009, the RHCE exam is a single section lasting 3.5 hours. Previously, it had been two sections lasting a combined 5.5 hours. The content has be consolidated and reorganized into a single section in which time is used more efficiently. The RHCE exam consists of RHCT components (essentially the RHCT exam) plus RHCE-specific components. It is possible to earn RHCT in an RHCE exam if one has met the RHCT requirements but not the RHCE ones.
The components are not always presented in the same sequence. The course instructor, who acts as the exam proctor, will determine the sequence and announce it early in the day. The three components are equally weighted at 100 points each. The minimum passing score is 240 points, or 80 percent. However, a candidate must score at least 50 points (50 percent) on each exam component to pass the exam. Red Hat advises candidates of their exam scores by e-mail within 10 business days of taking the exam.
Because the RHCE exam is performance-based, it’s crucial that you have, or develop, experience in working with Unix or Linux and related network services. This step by step guide is focus to get your RHCE certification by present practical exercises.
These exercises can be time-consuming, and you may feel that they’re unnecessary. However, unless you have extensive practical experience, you should perform every exercise. Often, exercises will lead you to discover subtle points not evident merely from reading the exercise. If your practical experience with Unix and Linux is small, you should construct and perform your own additional exercises. The RHCE exam tests for the equivalent of about two years of experience with Linux and networking. With diligent effort, you can accumulate that experience in a matter of weeks. However, doing so will require that you skimp nowhere.
LINUX BIOS :
When a microprocessor powers up, it starts executing instructions located in a ROM chip. These initial instructions are responsible for initializing the hardware (especially enabling RAM) and loading an operating system. The implementations and interfaces to this functionality vary from machine to machine, but its basic responsibility remains the same.
Here is an excellent Resource on-
For RHCE exams given on Red Hat Enterprise Linux 3 and higher, the exam is organized as follows:
Troubleshooting and System Maintenance — 2.5 hours
Installation and Configuration — 3.0 hours
In order to earn RHCE, one must successfully complete all the RHCT-level Troubleshooting and System Maintenance requirements, and successfully complete enough additional RHCE items to earn a score of 80 or higher overall on the section.
In addition, one must score 70 or higher on the RHCT items of Installation and Configuration, and 70 or higher on the RHCE components of that section. We describe the skills associated with RHCT and RHCE below.
For RHCE exams given on Red Hat Linux 9, the following structure applies:
Troubleshooting — 2.5 hours
Multiple Choice — 1.0 hour
Installation and Configuration — 2.5 hours
In order to earn RHCE on these exams, one must successfully complete all the RHCT-level Troubleshooting requirements, score a minimum of 50 on the multiple choice, score 70 or higher on both the RHCE and RHCT components, and earn an overall score of 80 or better for the exam as a whole.
[root@ice ~]# ifdown eth0
[root@ice ~]# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0C:29:2A:47:7F
inet addr:192.168.0.103 Bcast:192.168.0.255 Mask:255.255.255.0
BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:1899 errors:0 dropped:0 overruns:0 frame:0
TX packets:833 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:923925 (902.2 KiB) TX bytes:283867 (277.2 KiB)
Interrupt:10 Base address:0x1400
[root@ice ~]# ifup eth0
Determining IP information for eth0… done.
[root@ice ~]# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0C:29:2A:47:7F
inet addr:192.168.0.103 Bcast:192.168.0.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe2a:477f/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1900 errors:0 dropped:0 overruns:0 frame:0
TX packets:838 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:924267 (902.6 KiB) TX bytes:284517 (277.8 KiB)
Interrupt:10 Base address:0x1400