/etc/passwd
User account information.
/etc/shadow
Secure user account information.
/etc/group
Group account information.
/etc/gshadow
Secure group account information.
/etc/default/useradd
Default values for account creation.
/etc/shadow-maint/useradd-pre.d/*,
/etc/shadow-maint/useradd-post.d/*
Run-part files to execute during user addition. The
environment variable ACTION will be populated with useradd
and SUBJECT with the username. useradd-pre.d will be
executed prior to any user addition. useradd-post.d will
execute after user addition. If a script exits non-zero then
execution will terminate.
/etc/skel/
Directory containing default files.
/etc/subgid
Per user subordinate group IDs.
/etc/subuid
Per user subordinate user IDs.
/etc/login.defs
Shadow password suite configuration.
