How to crack passwords of Linux users!

How to crack passwords of Linux users!: In Linux, the passwords of the users will be encrypted with an algorithm called a shadow.
By using the unshadow algorithm we can get the hashes of the passwords.
Through these hashes, we can get the password by using a tool called john.
John will help to crack the hashes of the passwords.

Installing John The Ripper:

$ sudo apt-get install john


$ locate passwd

???? this command will help us to locate the directory of the password file

$ locate shadow

☝ this command will help to locate the shadow file.

$ man unshadow

???? the command helps to get the details of the “unshadow”.

Syntax to use unshadow ????:

$ unshadow passowrd-file shadow-file

This syntax helps to combine the shadow file and password file and the resultant will stored in file name called dump.


$ unshadow /etc/passwd /etc/shadow
$ unshadow /etc/passwd /etc/shadow > 1.txt
$ john 1.txt

Cracking using the wordlist:

The most used wordlist for cracking is “rockyou.txt”. This text file contains millions of the most used passwords.

$ john --wordlist=path_of_wordlist_file filename_of_hashes

Creating a custom wordlist using crunch:

Custom wordlists help us to create the wordlists of our style/pattern.
Installing crunch:

$ sudo apt-get install crunch

Syntax of crunch:

$ crunch min max charset options

min and max are the numbers which tells the min length and max length of the words. Character set for crunch:

  • Numeric
  • Alpha
  • Alpha-numeric
  • Loweralpha
  • Loweralpha numeric
  • Mix alpha
  • Mix alpha-numeric


$ crunch 1 8

This command will display a wprd list that starts with “a” and ends with “z” with a length of 1 to 8.

$ crunch 1 6 abcdefg

This command will display a wordlist that starts with “a” and ends with “g” with a length of 1 to 6.

$ crunch 2 3 lok123 -o /root/Desktop/3.txt

Here -o represents to send the wordlist to the specified file
This command will create an alpha-numeric wordlist that starts with length 2 and ends with length 3 and saves the wordlist in the file 3.txt.

$ crunch 4 5 -f /usr/share/rainbowcrack/charset.txt loweralpha-numeric -o /root/Desktop/4.txt

How to prevent this from attacker:

  • Limit the access to the file for the specific users.                                                                     Recommended: Only root user should have access to those files.
  • Keep yourself low: Use the normal use for your purposes.
  • Keep changing your passwords within 3 months.
  • Do not share your passwords with anyone.
  • Keep the passwords that can’t be guessed by the attacker.

Happy Hacking….!

–regards Lokesh Dachepalli

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