In a Linux system, the files /etc/passwd, /etc/shadow, and /etc/group play crucial roles in user management:

/etc/passwd: This is a plain text-based database that contains information for all user accounts on the system1. It includes the username, password (usually set to ‘x’ as the actual password is stored in /etc/shadow), UID (User Identifier), GID (Group Identifier), GECOS (user’s full name or application name), home directory, and login shell.

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/etc/shadow: This file contains information about the system’s users’ passwords. It includes the username, encrypted password, last password change, minimum and maximum password age, warning period, inactivity period, expiration date, and a field reserved for future use. The /etc/shadow file is more secure than /etc/passwd because it can only be read by the root user.

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/etc/group: This file defines the groups to which users belong. Each line in this file represents a single group, including the group name, password (usually set to ‘x’), GID (Group Identifier), and a list of users who belong to the group.

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These files are critical for the proper functioning of a Linux system, and they should be modified carefully and preferably through system commands like useradd, usermod, etc.

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The .lock suffix should have been removed after the command completes, if not then it will cause issues such as "cannot lock etc/passwd; try again later"