Create an account named useradd-u 0-o-g root-G root-d/home/user1 user1usermod-u 0-o-g root-G root-g root user1 in linux: -u 0: indicates that the uid is specified as 0 (0), which is the same as the root user. The prompt after logon is # rather than $. -O: this parameter must be specified because the uid already exists (it is the same as the uid of the root account. -G root: The group name of the initialization group. When a user belongs to multiple groups (specified in the-G parameter), the group in which the user logs on. By default, the system creates a new group with the same name as the user name and sets it as the group name during initialization. Regardless of the group specified by-G. -G root: list of groups to which the user name belongs. A user can belong to multiple groups. Group names are separated by commas (,). The group names must already exist. -D/home/user1: Specify the user's home directory user1 to create user1 test: You can use the id user1 command to test the attributes of user1: uid = 0 (root), gid = 0 (root), group = 0 (root) Description: gid indicates the initial GID.