How To Use Etc Shadow

Before we delve into the details of how the etc shadow file entries for some users could allow us to replicate their passwords across several machines let s first understand the different fields of the etc shadow file.

How to use etc shadow. All redhat and debian based linux os use shadow file to provide additional layer of security to user s password. Umask 077 unshadow r00tpasswd r00tshadow r00t4john now you can run john the ripper on the file mypasswd. To turn an etc shadow file into a normal unix password file use the unshadow utility from john the ripper. Unshadow is a tool that handles this task and it is part of the john package. Someday you may need to edit the etc shadow file manually to set or change ones password.

The etc shadow file supports all advanced algorithms and has plenty of room for further updates. The owner of the etc shadow file is usually the user root. This is because had the password were stored in etc passwd file even in encrypted format anyone could see decrypt and use them pretty easily. Etc shadow is a text file that contains information about the system s users passwords. Linux stores users encrypted passwords as well as other security information such as account or password expiration values in the etc shadow file.

It checks that all entries in etc passwd and etc shadow have the proper format and contain valid data. This file stores user s password in encrypted form. Unshadowing is a process where we combine the etc passwd file along with the etc shadow in order for john to be able to understand what we are feeding to it. Other users are not allowed to read the file directly to prevent them from gathering hashes passwords of others. The etc shadow file is readable only by root user.

When a user tries to login first of all the entered username is checked in the passwd file and when that. Thus passwords are actually stored in etc shadow file which can only be accessed by root or superuser and not made open to the entire world. The solution to this problem was to use the user entries from the etc shadow file. The most commonly used and standard scheme is to perform authentication against the etc passwd and etc shadow files. There are several different authentication schemes that can be used on linux systems.

Use the pwck command verifies the integrity of the users and authentication information. The group is often set to an administrative group like shadow. Unlike the etc passwd that is readable for everyone the etc shadow file must be readable by the root user only. The etc shadow file addresses all above issues. The process involves two basic steps the first is called unshadowing while the second is the cracking itself.