auth_mkhomedir() checks if the AUTH_MKHOMEDIR_SKEL environment variable is set, and if the authenticated account's home directory does not exist. If the environment variable is set it must point to a directory like /etc/skel that contains a template for the contents of a new account's home directory.

If AUTH_MKHOMEDIR_SKEL is not set, or if the home directory exists, auth_mkhomedir() does nothing and returns 0. Otherwise the account's home directory gets created, and the contents of the AUTH_MKHOMEDIR_SKEL directory get recursively copied into the new home directory. The permissions of AUTH_MKHOMEDIR_SKEL and its contents are preserved, and the owner userid and groupid is set to the authenticated account's userid and groupid.