Nmap Basics for system Administrator

The Nmap aka Network Mapper is an open source and a very versatile tool for Linux system/network administrators. Nmap is used for exploring networksperform security scansnetwork audit and finding open ports on remote machine. It scans for Live hosts, Operating systems, packet filters and open ports running on remote hosts.

Understanding Open, Closed and Filtered

Nmap has a variety of scan types, understanding how the default and most common SYN scan works is a good place to start to examine how the scan works and interpreting the results.

The 3 way TCP handshake

First a bit of background, during communication with a TCP service, a single connection is established with the TCP 3 way handshake. This involves a SYN sent to an TCP open port that has a service bound to it, typical examples are HTTP (port 80), SMTP (port 25), POP3 (port 110) or SSH (port 22).

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Alternative for DD command with a progress report about how much has been written-dcfldd

1 ) DD Command:-

The dd command stands for “data duplicator” and used for copying and converting data. It is very powerful low level utility of Linux which can do much more like.

• Backup and restore the entire hard disk or partition.
• Backup of MBR (Master Boot Record)
• It can copy and convert magnetic tape format, convert between ASCII and EBCDIC formats,swap bytes and can also convert lower case to upper case.
• It can also be used by Linux kernel make files to make boot images.

Only superuser can run this command because you can face a big data loss due to its improper usage, so you should be very careful while working with this utility. At that moment data loss can convert the dd utility as a “data destroyer” for you

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