Explain the fields in /etc/passwd and /etc/shadow ?

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.

steve:$1$XOdE07rn$WA6qFm4W5UIqNfaqE5Uub.:13775:0:99999:7:::

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

steve:x:6902:6902::/home/steve:/bin/bash

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).