Basic Linux commands cp mv rm mkdir cat cd command example


Basic Linux commands cp mv rm mkdir cat cd command example

In this assignment I will demonstrate some basic commands which are required to perform day to day task by user. In our last assignment we created a normal user named Vinita. Now login from Vinita, and try to find out what are the difference you noticed when you login from normal user.
normal user login linux
In bracket right most side is showing user name Vinita and beside @Server is the hostname of computer and further ~sign is showing that user is presently logged in her home directory. But first, every Linux user has a home directory. You can use the tilde (~) to represent the home directory of any currently active user. For example, if your username is Vinita, your home directory is /home/Vinita. If you have logged in as the root user, your home directory is /root. Thus, the effect of the cd ~command depends on your username. For example, if you have logged in as user Vickey, the cd ~ command brings you to the /home/Vickey directory. If you have logged in as the root user, this command brings you to the /root directory. You can list the contents of your home directory from anywhere in the directory tree with the ls ~ command. After bracket you can see the command prompt of normal user is $ sign.

$mkdir [ directory name ]

mkdir command is used to create new directory. Let’s create a example directory.
$mkdir example $ls example 
now create a file. Syntax for creating file is
 $cat > [file name]
This command can be used in three way to see the matter of file, to create a new file or to append the matter of file.
$cat [file name] ------------------------ To see the matter of file
$cat > [file name]---------------------- To create a file
$cat >> [file name ]-------------------- To append the matter of file
Be little bit careful while using cat > command to create new files. If you accidently used this command with existing file it will overwrite the matter of file. Use CTRL+D to save the matter of file.
Different use of cat command
$cat > test This is test of file
$cat test This is test of file
$cat >> test This is second line
$cat example This is test of file This is second line in test file
$cat > test Now file will over write
$cat test Now file will overwrite
basic  linux commands

$cd [ destination directory path]

It is easy to change directories in Linux. Just use cd and name the absolute path of the desired directory. If you use the relative path, just remember that your final destination depends on the present working directory.
basic linux commands
as you can see in the output of ls command file is in white color and directory is in blue color.
There are two path concepts associated with Linux directories: absolute paths and relative paths.
An absolute path describes the complete directory structure based on the top level directory, root (/).
A relative path is based on the current directory. Relative paths do not include the slash in front.
The difference between an absolute path and a relative one is important To know more about path and directory structure

pwd

In many configurations, you may not know where you are relative to the root (/) directory. The pwd command, which is short for print working directory, can tell you, relative to root (/). Once you know where you are, you can determine whether you need to move to a different directory.

$cd ..

this command is used to exit from current directory.

cp

The cp (copy) command allows you to take the contents of one file and place a copy with the same or different name in the directory of your choice. For example, the cp file1 file2 command takes the contents of file1 and saves the contents in file2. One of the dangers of cp is that it can easily overwrite files in different directories, without prompting you to make sure that's what you really wanted to do.
basic linux commands

mv

While you can't rename a file in Linux, you can move it. The mv command essentially puts a different label on a file. For example, the mv file1 file2 command changes the name of file1 to file2. Unless you're moving the file to a different partition, everything about the file, including the inode number, remains the same.

rm

rm command is used to remove the regular files. It will ask before removing files.

rmdir

it will remove the empty directory. If directory is full then use rm –rf [directory name]
basic linux commands

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Login linux terminal pwd ls useradd commands accessing virtual terminals


              

Login linux terminal pwd ls useradd commands accessing virtual terminals



In this assignment I will instruct you about some basic commands of Linux. You will get seven virtual terminal when you perform full installations. Although you can use graphics for daily task but here we are preparing for RHCE exam so you must use command line interface. Because all question are based on command line in RHCE Exam.

Virtual Consoles

A virtual console is a command line where you can log into and control Linux. As RHEL is a multi terminal operating system, you can log into Linux, even with the same user ID, several times. It's easy to open a new virtual console. Just use the appropriate ALT-function key combination. For example, pressing ALT-F2 brings you to the second virtual console. You can switch between adjacent virtual consoles by pressing ALT-RIGHT ARROW or ALT-LEFT ARROW. For example, to move from virtual console 2 to virtual console 3, press ALT-RIGHT ARROW.
You can switch between virtual terminals by just press the ALT+CTRL+Funcation key combinations.
ALT + CTRL + F1 for terminal 1
ALT + CTRL + F2 for terminal 2
ALT + CTRL + F3 for terminal 3
ALT + CTRL + F4 for terminal 4
ALT + CTRL + F5 for terminal 5
ALT + CTRL + F6 for terminal 6
ALT + CTRL + F7 for terminal 7
Terminal 7 is by default graphic mode beside it all six terminal are CLI based. Open any terminial by press ALT+CTRL+F1 key combinations. root account is automatically created when we install Linux.
default login screen
Type root on login name and press enter key, now give password ( no asterisk character like window to guess the password length) When you login from root account you will get # sign at command prompt , and when you login from normal user you will get $ prompt.
login in linux

#clear

This command is used to clear the screen.You have three options to logout .

Press CTRL+D

#exit

#logout

All three commands perform same task.

#pwd /root

linux basic command
Print working directory command will tell you about current location from / partition.

#ls

ls command will list the object in directory. All directory are listed in blue color while files are shown white color.

#ls –a

Normal ls command will not list the hidden files. If you want to list the hidden file use –a switch with ls command to list the hidden files.

#ls –l

Ls command with –l switch will list the objects in long formats . we will discuss more about –l switch in coming sections.

#ll

Same as ls –l . First and major task for any system administrator is user managements. For testing purpose you can perform all task with root account but in real life root account is used for administrative purpose only. Lest create a normal user account for further practical.

#useradd [user name ]

Useradd command is used to create user. Several advance options are used with useradd command but you will learn about them in coming article.
linux create user

#passwd [user name]

In linux no user can be login without password. passwd command is used to assign password for any user. Do not execute this command without user name otherwise it will change root password.

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Linux Unix Filesystems Directories Structure


Linux Unix Filesystems Directories Structure

Overview of the FHS

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.
/binEssential command line utilities. Should not be mounted separately; otherwise, it could be difficult to
 get to these utilities when using a rescue disk.
/bootIncludes 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.
/etcMost basic configuration files.
/devHardware and software device drivers for everything from floppy drives to terminals. Do not mount this directory on a separate partition.
/homeHome directories for almost every user.
/libProgram libraries for the kernel and various command line utilities. Do not mount this directory on a
 separate partition.
/mntThe mount point for removable media, including floppy drives, CD-ROMs, and Zip disks.
/optApplications such as WordPerfect or StarOffice.
/procCurrently running kernel-related processes, including device assignments such as IRQ ports, I/O
 addresses, and DMA channels.
/rootThe home directory of the root user.
/sbinSystem administration commands. Don't mount this directory separately.
/tmpTemporary files. By default, Red Hat Linux deletes all files in this directory periodically.
/usrSmall programs accessible to all users. Includes many system administration commands and utilities.
/varVariable 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:
  • Directories
  • Files
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 TypeDescription
Regular filesThese 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.
LinksThese files are pointers that point to other files in the file system.
FIFOsFIFO 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.
SocketsSockets 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

FileFunction
/etc/fstabLists the partitions and file systems that will be automatically mounted when the system boots.
/etc/groupContains local group definitions.
/etc/grub.confContains configuration parameters for the GRUB bootloader (assuming it's being used on the system).
/etc/hostsContains a list of hostname-to-IP address mappings the system can use to resolve hostnames.
/etc/inittabContains 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.confContains configuration parameters for your kernel modules.
/etc/passwdContains your system user accounts.
/etc/shadowContains encrypted passwords for your user accounts.
/etc/X11/Contains configuration files for X Windows.