The /etc/shadow file stores actual password in encrypted format with some additional properties related to user password.It mainly holds athe account aging parameters. All fields are separated by a colon (:) symbol. It contains one entry per line for each user listed in /etc/passwd file Generally, shadow file entry looks as below.
Here is the explanation of each field.
User name : Your login name
Password: Your encrypted password.
Last password change : Days since Jan 1, 1970 that password was last changed
Minimum: The minimum number of days required between password changes.
Maximum: The maximum number of days the password is valid.
Warn : The number of days before password is to expire that user is warned that his/her password must be changed
Inactive : The number of days after password expires that account is disabled
Expire : days since Jan 1, 1970 that account is disabled. It indicates an absolute date specifying when the login may no longer be used
The /etc/passwd file stores essential information, which is required during login /etc/passwd is a text file, that contains a list of user account related parameters like user ID, group ID, home directory, shell, etc.
Here is the sample entry from /etc/passwd file
Username: User's login name.
Password: An x character indicates that encrypted password is stored in /etc/shadow file.
User ID (UID): Each user must be assigned a user ID (UID). UID 0 (zero) is reserved for root.
Group ID (GID): The primary group ID
User Info: The comment field. It allow you to add extra information about the user.
Home directory: The absolute path to the directory the user will be in when they log in.
Command/shell: The absolute path of a command or shell (/bin/bash).