The /etc/passwd file stores local accounts of the system. It is a readable text file and uses colons (:) to separate the fields. This file helps with converting user IDs to names (and back). It is fine that all users can read this file, but they should not be able to change fields. Therefore, the mostcorrect permissions for /etc/passwd are
-rw-r-r-, which means that only the owner (root) can write to the file, and everyone can read it. The
/etc/shadow file contains information about the system's users' passwords. It is owned by user root and group shadow, and has 640 permissions. The password is stored as a long string of characters, which is a combination of the hashing algorithm, optional salt applied, and the hashed password itself. Other users are not allowed to read the file directly, to prevent them from gathering hashed passwords of others. Therefore, the most correct permissions for /etc/shadow are -r--------, which means that only the owner (root) can read the file, and no one else can read or write to it. References:

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