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10+ Network Commands in Linux for Troubleshooting [2020]

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Let’s Learn Network Commands in Linux with Practical Examples :

Computers use networks to communicate and share information with other resources. A computer network comprises two or more computers connected through different devices to complete the connectivity. It is the task of a System Administrator to set up and maintain the several functions within the network. We are going to look at 10 commonly used Network Commands in Linux for both network configuration and troubleshooting.

1. IFCONFIG (interface configurator)

Ifconfig is a Network Commands in Linux used to check network interface configurations. The common application of this command is to check the IP address assigned to the system. You can also use this command to enable or disable a network interface. This single command also gives in details the Hardware or MAC address and the MTU –maximum transmission unit.

In the example above the IP address (inet addr) is: 192.168.0.14, the MAC address (HWaddr) is: 0b4:99:ba:e8:34:f4
The ifconfig takes several options, using the ifconfig option will give the status of the interface whether it is enabled or disabled. For example.

Other uses of the ifconfig command are as follows:

Assigning IP Address and netmask

For example,

Enabling or disabling a network interface

Enabling a network interface:

Disabling a network interface:

Please note that eth0 can be replaced by the interface name assigned to your machine, in my case it is enp0s25

Setting the MTU size (the default value of MTU is 1,500)

Where xxx is the numerical value assigned

Finally, to set the network interface to receive all packet and check later you set it in promiscuous mode as follows:

The above command requires superuser privileges.

2. PING (Packet Internet Groper Command) Command

The best way to analyze network connectivity between two communication interfaces. PING works in any network setup whether it is a LAN or WAN. The protocol used by PING is called the ICMP (Internet Control Message Protocol) to send between nodes.

OR using a host name

When executed in Linux, PING command will not stop until you issue the interrupt command using the –c option. Using a number N will issue an interrupt after N PINGs.

3. TRACEROUTE

Traceroute is used to trace the network path by showing the number of hops taken to reach its destination. This example shows the path taken by the global DNS Server IP Address tracing its path and destination.

4. NETSTAT (Network Statistics)

Display information on the connection and routing table. Displaying the routing table data add the –r option.

Using the –r Option

5. DIG (Domain Information Groper)

This command will query for DNS related data such as the A Record, MX record, CNMAE, etc.

6. NSLOOKUP

Is also another command used to query the DNS. This example queries the domain name server.

7. ROUTE

This command is used to show the IP routing table. Using it will give you the default routing table.

The command can also add, delete, and set the default gateway as follows:

Adding Routes

Deleting Routes

Setting the default gateway

8. HOST

The host command is used to find the name of associated to a particular IP address or an IP associated to a specific IP. The HOST command searches in the IPv4 or IPv6 and the DNS records.

9. ARP (Address Resolution Protocol)

System administrators use this command to view or add the contents of a kernel to the ARP table. The default table is viewed by using it in the following format using the –e option

10. ETHTOOL

This command was known by the name mii-tool and later on changed to ethtool. The command is used to view Ethernet adapter settings. For example, to view adapter settings for eth0, run

Settings for eth0:

To display device driver run

Sample output

The above Network Commands in Linux should be able to help you troubleshoot your network issues by gathering network information and diagnose an impending problem. This article is meant for use on a day to day for Linux Network Administrator or anyone used to the Linux operating system.

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1 Comment

1 Comment

  1. bladez123

    February 10, 2020 at 3:15 am

    bmon is a powerful, command line based network monitoring and debugging utility for Unix-like systems, it captures networking related statistics and prints them visually in a human friendly format. It is a reliable and effective real-time bandwidth monitor and rate estimator.

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Linux

Linux sed command with usage examples [2020]

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Short for stream editor, the Linux sed command is a useful utility used for manipulation text output. You can use it for substituting text, finding and replacing text, searching text and so much more. The command accord you the ability to edit files without having to open them. In this tutorial, we look at various ways you can use the Linux sed command.

1) Replacing or substituting strings

To elaborate on how the command can be used for text manipulation, we are going to use a sample text file linuxgeek.txt with the content below:

To replace all instances of the word Unix with Linux, run the command:

Output

Linux sed command

The ‘s’ flag stands for substitution. In the command above, the first instance of the word ‘Unix’ is replaced by ‘Linux’. By default, the substitution happens to the first string occurrence only, and not the subsequent occurrences.

2) Replace the nth occurrence of a word in a line

To replace the nth occurrence of a string in a file, you need to use the /nth flag. For example, to replace the 2nd occurrence of a string in a line, issue the command:

Output

In the example above, the second instance of the string ‘Unix’ has been replaced by ‘Linux’ in the 1st and 4th lines.

3. Substitute all instances of a string in a file

If you want to replace all instances of the string to be substituted, in this case, ‘Unix’ use the /g option. The ‘g’ stands for global and instructs sed to replace all the instances of the string.

Output

4) Replace a string on a specific line number

Additionally, you can instruct the Linux sed command to replace the keyword in a particular line. For example to replace the string in the 4th line only, use the command:

Output

Linux sed command

As observed, only the first instance is substituted. To substitute all the occurrences of the string, simple append ‘g’ after the last forward slash as shown:

Output

Linux sed command

5) Substitute a string in a range of lines

You can also opt to replace the search keyword for a range of lines, for example between lines 1 and 3. To accomplish this, issue the command:

Output

From the output above, we can observe that the substitution has only occurred in lines 1-3. The last line remains unchanged.

6) Print lines where substitution has occurred

To print the lines where substitution of the lines has occurred, use the -n flag immediately after the sed command as shown:

Output

7) Delete lines using Linux sed command

Sed command can also be used for deleting lines. This is possible using the ‘d’ flag. To delete the 3rd line, for example, run the command:

Output

To delete the last line only in the file, we are going to run the command:

8) Delete the last line

Output

9) Delete a range of lines

To delete a range of lines. for instance from 2 to 4 in a text file, run the command:

Output

10) Add blank lines or spaces

To add a blank line after every line run the command:

linux sed command

This wraps up our tutorial today. We have showcased some of the commonly used cases of the stream editor sed command.

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Linux

cat command in Unix/Linux with 10+ examples [2020]

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Let’s Learn cat command in Unix/Linux with Practical Examples :

The cat command in Unix/Linux is one of the most commonly used Linux commands on a day-to-day basis whether by novices or experienced Linux users. cat is short for concatenating and is mainly used for creating either single or several files at an instance, or viewing the contents of a file. In this article, we dive deeper and explore the cat command in Unix/Linux with example usages.

Cat command in Linux with examples

The most basic syntax for using cat command is as shown below

Let’s now take a closer look at the options that are mostly used with the cat command.

1. To view file content using cat command

To have a peek at a file without any options, simply use the syntax

For instance, to check the contents of a file /etc/hosts/code> run the command:

Sample output

cat command in Unix/Linux

2. View Mutiple files in a single command

To view multiple files at a go with cat command, use the syntax:

For example

Sample output

cat command in Linux

3. Display line numbers using the -n option

To make your display neater, and more presentable, you may want to number the lines of your output. To achieve this, use the -n option as shown below

For instance

Sample output

cat command in Unix/Linux

4. Create a file using the cat command

To create a file using cat command use the syntax

Next, type the contents of the file and finally hit CTRL +D to save the file

cat command in Linux create a new file

5. Copy contents of one file onto another

With cat command, you can easily copy file contents of one file into another using the standard redirection operator > as shown below.

If the file being copied to does not exist, it will be created automatically.

cat command in Linux

NOTE

Extra caution should be taken while using the standard redirection operator because it overwrites the contents of an existing file.

6. Redirect several files into one file

Similarly, you can redirect content from multiple files into one file using the syntax:

Sample output

7. Appending text to a file

if you want to append text and not overwrite the existing content, use the double greater sign symbol (>>). The content of one file will be added or appended at the end of the next text file.

8. Redirect standard input using redirection operator

you can use the redirection operator less than (<) to read contents from a file. The syntax for this is:

Sample output

9. Display the ‘$’ sign at the end of every line

If you wish to display the $ at the end of every line, use the -e option as shown below:

Sample output

From the output above, you can see that there a dollar sign ($) at the end of every file.

10. Display all files of a certain type

To display the content of all files of a certain file type, for example, text files use the wildcard symbol as seen in the command below

Sample output

As you can see from the output above, the command displays all content from all the text files with a .txt file extension.

Take away

In this article, we demonstrated the usage of cat command alongside some helpful examples and tips. The cat command is usually helpful in creating and viewing text files as well as appending content at the end of a file. We do hope that this tutorial was helpful. Fee free to try out some of the commands.

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Linux

Whereis command in Linux with 10+ Examples [2020]

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Let’s Learn whereis command in Linux with Simple Examples :

While working away on the command-line, one might need to find out the location of a command or binary file. The find command can be used for this task, but it is painfully slow and ends up taking much of your time and may also provide undesired results. The whereis command in Linux is ideal for quickly finding the location of a binary or source file in a system.

Whereis command in Linux is preferred due to its speed and accuracy in finding out the location of a command or binary files. More importantly, running the whereis command doesn’t require you to have root privileges. Let’s dive in and take a look at the whereis command usage with examples.

Whereis command usage in Linux

The basic syntax of the whereis command is:

1) Find the location of a command

To find out the location and man pages of a Linux command for instance,mkdir run the command

Sample output

whereis command in linux

2) Search for specific files/manuals

If you wish narrow down your search specifically to the binary file, use the -b option as shown in the command below.

Sample output

whereis command usage

To search for man pages only use the -m option as shown.

Sample output

3) View paths that whereis uses for searching

To take a quick peek at the directories that whereis command traverses while searching for command , files and man pages, use the -l option.

Sample output

whereis command in linux

4) Limit the search depth for whereis command

Usually, whereis command searches for commands and files in well-defined, hard-coded paths. However, you can limit the search depth using the -B option. For instance, to limit whereis to search binary files up to /bin, use the -B option as shown:

the -f option terminates the directory list whilst signaling the beginning of file names.

To limit the search directory for man pages, use the -M option as shown

Sample output

5) Check whereis version

if you wish to check the version of whereis command, use the -V option or –version flag as shown.

OR

Sample output

whereis command usage

6) Display whereis help options

To view the help page section that gives more insight on the options that can be used by whereis command, use the -h option or –help flag.

OR

Sample output

And with that, we come to the end of our tutorial. We welcome you to try out the commands and get back to us with your findings.

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