Important Linux Commands

This section gives insight into the most important commands of your SuSE Linux system. Along with the individual commands, parameters are listed and, where appropriate, a typical sample application is introduced. To learn more about the various commands, it is usually possible to get additional information with the man program followed by the name of the command, for example, man ls.

In these manual pages, move up and down with PgUp and PgDn and move between the beginning and the end of a document with Home and End. End this viewing mode by pressing Q. Learn more about the man command itself with man.

There are many more commands than listed in this blog. For information about other commands or more detailed information, we recommend the O'Reilly publication RHCE Training in Jaipur in a Nutshell. In the following overview, the individual command elements are written in different typefaces.

• The actual command is always printed as command. Without this, nothing can function.
• Options without which the respective program cannot function are printed in italics.
• Further details, like file names, which must be passed to a command for correct functioning, are written in the Courier font.
• Specifications or parameters that are not required are placed in [brackets].

Adjust possible specifications to your needs. It makes no sense to write ls file(s), if no file named file(s) actually exists. You can usually combine several parameters, for example, by writing ls -la instead of ls -l -a.

File Commands

File Administration

ls [option(s)] [file(s)]

If you run ls without any additional parameters, the program will list the contents of the current directory in short form.

-l

detailed list

-a

displays hidden files

cp [option(s)] sourcefile targetfile

Copies sourcefile to targetfile.

-i

Waits for confirmation, if necessary, before an existing targetfile is overwritten

-r

Copies recursively (includes subdirectories)

mv [option(s)] sourcefile targetfile

Copies sourcefile to targetfile then deletes the original sourcefile.

-b

Creates a backup copy of the sourcefile before moving

-i

Waits for confirmation, if necessary, before an existing targetfile is overwritten

rm [option(s)] file(s)

Removes the specified files from the file system. Directories are not removed by rm unless the option -r is used.

-r

Deletes any existing subdirectories

-i

Waits for confirmation before deleting each file.

ln [option(s)] sourcefile targetfile

Creates an internal link from the sourcefile to the targetfile, under a different name. Normally, such a link points directly to the sourcefile on one and the same file system. However, ifln is executed with the -s option, it creates a symbolic link that only points to the directory where the sourcefile is located, thus enabling linking across file systems.

-s

Creates a symbolic link

cd [options(s)] [directory]

Changes the current directory. cd without any parameters changes to the user's home directory.

mkdir [option(s)] directoryname

Creates a new directory.

rmdir [option(s)] directoryname

Deletes the specified directory, provided it is already empty.

chown [option(s)] username.group file(s)

Transfers the ownership of a file to the user with the specified user name.

-R

Changes files and directories in all subdirectories.

chgrp [option(s)] groupname file(s)

Transfers the group ownership of a given file to the group with the specified group name. The file owner can only change group ownership if a member of both the existing and the new group.

chmod [options] mode file(s)

Changes the access permissions.

The mode parameter has three parts: group, access, and access type. group accepts the following characters:

u

user

g

group

o

others

For access, access is granted by the + symbol and denied by the - symbol.

The access type is controlled by the following options:

r

read

w

write

x

eXecute — executing files or changing to the directory.

s

Set uid bit — the application or program is started as if it were started by the owner of the file.

gzip [parameters] file(s)

This program compresses the contents of files, using complex mathematical algorithms. Files compressed in this way are given the extension .gz and need to be uncompressed before they can be used. To compress several files or even entire directories, use the tar command.

-d

decompresses the packed gzip files so they return to their original size and can be processed normally (like the command gunzip).

tar options archive file(s)

The tar puts one file or (usually) several files into an archive. Compression is optional.

tar is a quite complex command with a number of options available. The most frequently used options are:

-f

Writes the output to a file and not to the screen as is usually the case

-c

Creates a new tar archive

-r

Adds files to an existing archive

-t

Outputs the contents of an archive

-u

Adds files, but only if they are newer than the files already contained in the archive

-x

Unpacks files from an archive (extraction)

-z

Packs the resulting archive with gzip

-j

Compresses the resulting archive with bzip2

-v

Lists files processed

The archive files created by tar end with .tar. If the tar archive was also compressed using gzip, the ending is .tgz or .tar.gz. If it was compressed using bzip2, .tar.bz2.

Application examples can be found in Section “Archives and Data Compression”.

locate pattern(s)

The locate command can find in which directory a specified file is located. If desired, use wild cards to specify file names. The program is very speedy, as it uses a database specifically created for the purpose (rather than searching through the entire file system). This very fact, however, also results in a major drawback: locate is unable to find any files created after the latest update of its database.

The database can be generated by root with updatedb.

updatedb [options(s)]

This command performs an update of the database used by locate. To include files in all existing directories, run the program as root. It also makes sense to place it in the background by appending an ampersand (&), so you can immediately continue working on the same command line (updatedb &).

find [option(s)]

The find command allows you to search for a file in a given directory. The first argument specifies the directory in which to start the search. The option -name must be followed by a search string, which may also include wild cards. Unlike locate, which uses a database, find scans the actual directory.

Commands to Access File Contents

cat [option(s)] file(s)

The cat command displays the contents of a file, printing the entire contents to the screen without interruption.

-n

Numbers the output on the left margin

less [option(s)] file(s)

This command can be used to browse the contents of the specified file. Scroll half a screen page up or down with PgUp and PgDn or a full screen page down with Space. Jump to the beginning or end of a file using Home and End. Press Q to exit the program.

grep [option(s)] searchstring filenames

The grep command finds a specific searchstring in the specified file(s). If the search string is found, the command displays the line in which the searchstring was found along with the file name.

-i

Ignores case

-l

Only displays the names of the respective files, but not the text lines

-n

Additionally displays the numbers of the lines in which it found a hit

-l

Only lists the files in which searchstring does not occur

diff [option(s)] file1 file2

The diff command compares the contents of any two files. The output produced by the program lists all lines that do not match.

This is frequently used by programmers who need only send their program alterations and not the entire source code.

-q

Only reports whether the two given files differ

File Systems

mount [option(s)] [<device>] mountpoint

This command can be used to mount any data media, such as hard disks, CD-ROM drives, and other drives, to a directory of the Linux file system.

-r

mount read-only

-t filesystem

Specifies the file system. The most common are ext2 for Linux hard disks, msdos for MS-DOS media, vfat for the Windows file system, and iso9660 for CDs.

For hard disks not defined in the file /etc/fstab, the device type must also be specified. In this case, only root can mount. If the file system should also be mounted by other users, enter the option user in the appropriate line in the /etc/fstab file (separated by commas) and save this change. Further information is available in mount.

umount [option(s)] mountpoint

This command unmounts a mounted drive from the file system. To prevent data loss, run this command before taking a removable data medium from its drive. Normally, only root is allowed to run the commands mount and umount. To enable other users to run these commands, edit the /etc/fstab file to specify the option user for the respective drive.

System Commands

System Information

df [option(s)] [directory]

The df (disk free) command, when used without any options, displays information about the total disk space, the disk space currently in use, and the free space on all the mounted drives. If a directory is specified, the information is limited to the drive on which that directory is located.

-H

shows the number of occupied blocks in gigabytes, megabytes, or kilobytes — in human-readable format

-t

Type of file system (ext2, nfs, etc.)

du [option(s)] [path]

This command, when executed without any parameters, shows the total disk space occupied by files and subdirectories in the current directory.

-a

Displays the size of each individual file

-h

Output in human-readable form

-s

Displays only the calculated total size

free [option(s)]

The command free displays information about RAM and swap space usage, showing the total and the used amount in both categories.

-b

Output in bytes

-k

Output in kilobytes

-m

Output in megabytes

date [option(s)]

This simple program displays the current system time. If run as root, it can also be used to change the system time. Details about the program are available in date.

Processes

top [options(s)]

top provides a quick overview of the currently running processes. Press H to access a page that briefly explains the main options to customize the program.

ps [option(s)] [process ID]

If run without any options, this command displays a table of all your own programs or processes — those you started. The options for this command are not preceded by hyphen.

aux

Displays a detailed list of all processes, independent of the owner.

kill [option(s)] process ID

Unfortunately, sometimes a program cannot be terminated in the normal way. However, in most cases, you should still be able to stop such a runaway program by executing the killcommand, specifying the respective process ID (see top and ps).

kill sends a TERM signal that instructs the program to shut itself down. If this does not help, the following parameter can be used:

-9

Sends a KILL signal instead of a TERM signal, with which the process really is annihilated by the operating system. This brings the specific processes to an end in almost all cases.

killall [option(s)] processname

This command is similar to kill, but uses the process name (instead of the process ID) as an argument, causing all processes with that name to be killed.

Network

ping [option(s)] host name|IP address

The ping command is the standard tool for testing the basic functionality of TCP/IP networks. It sends a small data packet to the destination host, requesting an immediate reply. If this works, ping displays a message to that effect, which indicates that the network link is basically functioning.

-c

number Determines the total number of packages to send and ends after they have been dispatched. By default, there is no limitation set.

-f

flood ping: sends as many data packages as possible. A popular means, reserved to root, to test networks.

-i

value Specifies the interval between two data packages in seconds. Default: one second

nslookup

The Domain Name System resolves domain names to IP addresses. With this tool, send queries to information servers (DNS servers).

telnet [option(s)] host name or IP address

Telnet is actually an Internet protocol that enables you to work on remote hosts across a network. telnet is also the name of a Linux program that uses this protocol to enable operations on remote computers.  not use telnet over a network on which third parties can eavesdrop. Particularly on the Internet, use encrypted transfer methods, such as ssh, to avoid the risk of malicious misuse of a password (see the man page for ssh).

Miscellaneous

passwd [option(s)] [username]

Users may change their own passwords at any time using this command. Furthermore, the administrator root can use the command to change the password of any user on the system.

su [option(s)] [username]

The su command makes it possible to log in under a different user name from a running session. When using the command without specifying a user name, you will be prompted for theroot password. Specify a user name and the corresponding password to use the environment of the respective user. The password is not required from root, as root is authorized to assume the identity of any user.

halt [option(s)]

To avoid loss of data, you should always use this program to shut down your system.

reboot [option(s)]

Does the same as halt with the difference that the system performs an immediate reboot.

clear

This command cleans up the visible area of the console. It has no options.

Logical Volume Manager

1. Why LVM is required ?

LVM stands for Logical Volume Manager , to resize filesystem’s size online we required LVM partition in Linux. Size of LVM partition can be extended and reduced using the lvextend & lvreduce commands respectively.

 2. Is it possible to increase the logical volume on fly ?

YES

3. How to reduce the logical volume ? is it possible to reduce on fly ?
Answer: No.You can’t reduce the logical volume on fly. Here is the steps to reduce the logical volume on redhat Linux.

•    Un-mount the filesystem
•    Run e2fsck on the volume device
•    Reduce the Filesystem.(resize2fs)
•    Reduce the logical Volume(lvreduce)
•    Mount the filesystem back for production.

4. What are steps to perform in order to increase the logical volume on fly ?

•       Extend the logical volume
•       Increase the Filesystem size
•       Verify the status using df command or lvs command.

5. .How to rename volume Group ? can we rename the VG on fly ? 
Yes. Its possible to rename the volume group on fly.But the mounted volumes will not reflect the same unless you re-mount the volume with new VG name.

Need to update the /etc/fstab with new VG name to mount the volumes across the system reboot.

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RHCE Training in Jaipur

Today most of the companies working on Linux operating system and Linux servers, so the requirement of Red Hat certifications is automatically increase. RHCSA (Red Hat Certified System Administration), RHCE (Red Hat Certified Engineer) and RHCA (Red Hat Certified Architect). RHCSA is a starting/associate level certification, RHCSA certification shows the technical skills of aspirants on live systems and main task are configuration, installation, troubleshooting as well as maintaining.

RHCE is next level of Red Hat certification and passing the RHCSA exam is a requirement for this certification. Red Hat Certified Engineer is the professional levels where the aspirant will get learn advance level troubleshooting and management techniques. In this level one can get a proper insight into the kernel configuration, network configuration, mail services and virtualization. RHCE training provides good level of knowledge to face advance challenges. RHCE certification proves high level of knowledge and is a highly respected and valued qualification. After RHCE certification candidate deserve a better opportunities. 

RHCA is a very high/expert level certification and this focus on expert topics of Linux administration and usage. For RHCA certification you have to clear RHCE certification exam.

LinuxWorld Informatics Pvt. Ltd. is starting Red Hat certification Training for IT Students like B.Tech, B.E, MCA, M.Sc., BCA, B.Sc. etc. We are authentic partner of Red Hat. We offer all the Red Hat certification training and exam like RHCSA, RHCE and RHCA. We have best Red Hat certified instructor. The main advantage of Training program for trainee, they learn and work with practical examples in supervision of experienced experts.

Best Purposes To Switch To Linux

 

1. It Doesn’t Crash

Linux has been time-proven to be a reliable working system. Despite the fact that the personal computer is not a brand new position for Linux, such a lot Linux-primarily based programs have been used as servers and embedded systems. High-visibility Web sites corresponding to Google use Linux-based totally techniques, however you can also to find Linux inside the TiVo set-best box in many livingrooms.
Linux has proved to be so dependable and secure that it is commonly found in devoted firewall and router systems utilized by high-profile companies to protected their networks. For more than ten years, it has no longer been uncommon for Linux systems to run for months or years with no need a single reboot.

2. Viruses Are Few and Some distance Among

Even though it’s conceivable to create a virulent disease to target Linux systems, the design of the system itself makes it very difficult to become infected. A single person may just cause local harm to his or her recordsdata by means of working a virus on his or her gadget; however, this may be an remoted instance somewhat than one thing could unfold out of control.
As well as, virtually all Linux companies be offering free on-line security updates. The overall philosophy of the Linux neighborhood has been to handle possible safety issues earlier than they develop into a problem moderately than hoping the susceptibility will move unnoticed.

3. Nearly Hardware-Unbiased

Linux was once designed and written to be easily moveable to other hardware. For the laptop person, because of this Linux has been and most probably at all times will be the first working system to take advantage of advances in hardware era comparable to AMD’s sixty four-bit processor chips.

4. Freedom of Selection

Linux provides freedom of choice as far as which producer you purchase the device from in addition to which application techniques you need to use. Being able to pick the manufacturer way you have a real choice as far as type of enhance you receive. Being open-supply software, new producers can input the marketplace to handle customer needs.

Number of software methods implies that you can choose the tools that perfect cope with your needs. For instance, three popular phrase processors are available. All three are loose and interoperate with Microsoft Phrase, but each and every offers unique advantages and disadvantages. The same is true of Web browsers.

5. Standards

Linux itself and lots of not unusual programs follow open standards. This means an replace on one system won’t make different programs obsolete.

6. Programs, Packages, Packages

Each Linux distribution comes with loads and possibly thousands of software systems included. This alone can prevent lots of dollars for each and every computer system you configure. Even though this can be a very small subset, imagine that the OpenOffice.org place of business suite is incorporated in addition to the GIMP, a software similar to (and many of us say more able than Adobe Photoshop); Scribus, a document structure software similar to Quark Xpress; Evolution, an e mail device similar to Microsoft’s Outlook Specific; and loads more.

For the more technically prone, development equipment, such as compilers for the C, C++, Ada, Fortran, Pascal and different languages, are integrated as well as Perl, PHP and Python interpreters. Editors and versioning gear are also included on this category.
Whether you might be looking for Instant Messaging clients, backup gear or Internet site construction applications, they most likely are all included within your base Linux distribution.

7. Interoperability

Increasingly computer systems are being hooked up to networks. No gadget could be complete if it didn’t come with equipment to allow it to interoperate with computer systems operating different working systems. Once once more, Linux could be very robust in this area.
Linux includes Samba, software that permits Linux to act as a client on a Microsoft Home windows-primarily based network. In fact, Samba includes server amenities such that that you must run a Linux system because the server for a gaggle of Linux and Home windows-based totally shopper systems.
In addition, Linux contains software to network with Apple networks and Novell’s Netware. NFS, the networking era developed on UNIX techniques also is included.

 

8. It is a Community Relationship, No longer a Consumer Relationship

Other working systems are the products of single vendors. Linux, then again, is brazenly advanced, and this technology is shared amongst vendors. This means you transform part of a community rather than a consumer of a single manufacturer. Additionally, the provider community easily can modify to the wishes of quite a lot of user communities reasonably than spouting a “one size suits all” philosophy.
This means you can select a Linux seller that appears to easiest deal with your wishes and really feel confident that it’s essential to transfer companies at a later time with out shedding your funding–both relating to prices and learning.

9. It’s No longer How Massive Your Processor Is…

As a result of a combination of the inner design of Linux and construction contributions from a various neighborhood, Linux tends to be more frugal in the usage of pc resources. This will likely take place itself in one personal computer system operating faster with Linux than with every other working gadget, however the advantages move a ways beyond that. It is imaginable, for instance, to configure a single Linux machine to act as a terminal server and then use outdated hardware as what are called thin clients.
This server/thin client configuration makes it imaginable for older, much less robust hardware to share the tools of an unmarried tough device thus extending the lifetime of older machines.

10. Linux Is Configurable

Linux is a real multi-consumer working system. Every person will have his or her own particular person configuration all on one computer. This includes the look of the desktop, what icons are displayed, what methods are began robotically whilst the person logs in and even what language the computer is in.

 

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RHCE Exam Objectives

RHCE exam candidates should be able to accomplish the following without assistance. These have been grouped into several categories.

System Configuration and Management

• Route IP traffic and create static routes
• Use iptables to implement packet filtering and configure network address translation (NAT)
• Use /proc/sys and sysctl to modify and set kernel run-time parameters
• Configure system to authenticate using Kerberos
• Build a simple RPM that packages a single file
• Configure a system as an iSCSI initiator that persistently mounts an iSCSI target
• Produce and deliver reports on system utilization (processor, memory, disk, and network)
• Use shell scripting to automate system maintenance tasks
• Configure a system to log to a remote system
• Configure a system to accept logging from a remote system

Network Services

Network services are an important subset of the exam objectives. RHCE candidates should be capable of meeting the following objectives for each of the network services listed below:

• 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

RHCE candidates should also be capable of meeting the following objectives associated with specific services:

HTTP/HTTPS

• Configure a virtual host
• Configure private directories
• Deploy a basic CGI application
• Configure group-managed content

DNS

• Configure a caching-only name server
• Configure a caching-only name server to forward DNS queries
• Note: Candidates are not expected to configure master or slave name servers

FTP

• Configure anonymous-only download

NFS

• Provide network shares to specific clients
• Provide network shares suitable for group collaboration

SMB

• Provide network shares to specific clients
• Provide network shares suitable for group collaboration

SMTP

• Configure a mail transfer agent (MTA) to accept inbound email from other systems
• Configure an MTA to forward (relay) email through a smart host

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SSH

 

• Configure key-based authentication
• Configure additional options described in documentation                

Reference:

https://www.redhat.com/certification/rhce/objectives/

Managing Partition in Linux using Parted

Parted is another utility  for managing  hard in linux based os

Step 1:-  To check number of partition  in a hard disk
======

[root@desktop12 ~]# parted  /dev/sda print  
Model: ATA ST3160812AS (scsi)
Disk /dev/sda: 160GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type      File system     Flags
 1      1049kB  538MB   537MB   primary   ext4            boot
 2      538MB   79.2GB  78.6GB  primary                   lvm
 3      79.2GB  79.7GB  537MB   primary   linux-swap(v1)
 4      79.7GB  160GB   80.3GB  extended
 5      79.7GB  82.9GB  3221MB  logical
 6      82.9GB  137GB   53.7GB  logical
 7      137GB   137GB   105MB   logical   ext3
 8      137GB   137GB   524MB   logical   ext4
 9      137GB   138GB   524MB   logical   ext4
10      138GB   140GB   2147MB  logical   ext4
11      140GB   140GB   105MB   logical
12      140GB   140GB   41.9MB  logical
13      140GB   141GB   524MB   logical
14      141GB   143GB   2147MB  logical   ext4

OR
==

[root@desktop12 ~]# parted  /dev/sda 
GNU Parted 2.1
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print                                                            
Model: ATA ST3160812AS (scsi)
Disk /dev/sda: 160GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type      File system     Flags
 1      1049kB  538MB   537MB   primary   ext4            boot
 2      538MB   79.2GB  78.6GB  primary                   lvm
 3      79.2GB  79.7GB  537MB   primary   linux-swap(v1)
 4      79.7GB  160GB   80.3GB  extended
 5      79.7GB  82.9GB  3221MB  logical
 6      82.9GB  137GB   53.7GB  logical
 7      137GB   137GB   105MB   logical   ext3

Step 2: To show create  a new  logical partition 
===================================================

Inside your  hard disk create partition of  2GB

(parted) mkpart  logical  143GB   145GB

Note: quit to exit from partition table

fire partx command to 
[root@desktop12 ~]# partx  -a /dev/sda

step 3: create file system  of desired format 
=============================================

[root@desktop12 ~]# mkfs.vfat   /dev/sda15

step 4: Now mount your partition 
=================================
[root@desktop12 ~]# mkdir  /media/kkk
[root@desktop12 ~]# mount  /dev/sda15  /media/kkk

Now you can save your data and can also made entry in /etc/fstab to make this partition persistance

Article Source - http://www.rhce.co.in/managing-partition-in-linux-using-parted/ 

Linux - Open Source Operating System

At the heart of all software is source code - the programs that perform basic functions. With open source software, this code is protected by a special license that ensures everyone has access to that code. That means no one company can fully own it. Freedom means choice. Choice means power.

That's why we believe open source is inevitable. It returns control to the customer. You can see the code, change it, and learn from it. Bugs are quickly found and quickly fixed. And when customers don't like how one vendor is serving them, they can choose another without overhauling their infrastructure. No more technology lock-in. No more monopolies.

We believe the open source model builds higher quality, more secure, more easily integrated software. And it does it at a vastly accelerated pace - often at a lower cost.

Open source spans platforms, middleware and applications. From data center to desktop. We help enterprises take full advantage of the capability and cost savings of open source-letting them do more with the technology they already have.

The subscription model allows Red Hat to have a mutually beneficial, cyclical relationship with customers:
Deliver new technology as soon as it's available.

Provide unlimited support at no additional cost.
And finally, the feedback we get from regularly working with you helps us deliver better technology tomorrow.

The benefits of choosing Red Hat
Red Hat is a leading contributor to the development of open source software. In fact, as noted by a couple of recent surveys, Red Hat is the leading corporate contributor to the most important open source project of all, the Linux kernel. Because Red Hat is the largest corporate contributor to the kernel, and able to influence features and strategy, this is an area where Red Hat is well-positioned.

A huge ecosystem of hardware and software partners offers both services and certified solutions, in collaboration with the industry leader. This powerful combination provides:

Thousands of certified applications from Independent Software Vendors (ISVs)
  Hundreds of certified hardware systems and peripherals from leading OEM vendors, spanning multiple processor architectures

Comprehensive service offerings with up to 24x7 support and a 1-hour response time, available from Red Hat and selected ISV/OEM partners

Excellent performance, security, scalability, and availability, with audited industry benchmarks
Open source technologies that are rigorously tested and matured through the Red Hat-sponsored Fedora project.

Quantum is proud to announce its partnership with Red Hat for much in demand RedHat certified Engineer (RHCE) and RedHat certified System Administrator (RHCSA) programs. These certifications provide demonstrated knowledge, skill and ability required to handle the Red Hat Enterprise Linux systems.