Joining a computer to an already established domain:
you cannot use a default admin account. if this is the only account on the machine, create a new user, and follow the steps once logged into that user.
you will also need a domain admin user from the domain to authorize the join
go to system properties > bottom right > change > input a name for the computer, cannot be the same as others on the domain > beneath the name, select domain and type the name of the domain you wish to join
a login will put up for authorization. use the login of the domain admin , not the local admin, or user you are currently logged into
you will need to reboot.
for windows server versions, the process is the same, except it will be in server manager, on the top left under 'domain'.
To promote a window server to a domain controller:
Add the ADDS role with server manager / roles and features. click through the process, self-explanatory.
once the roles install, go back to sever manager > top right flag > promote this server to a domain controller
make sure the domain is correct and the user is a domain admin , not your local admin, local user, or default admin. click through the rest of the process. the server will reboot when complete.
To demote a windows server (must have 2 other DCs)
server manager > top right 'manage' > remove roles and features > click through to 'server roles' and remove ADDS
you will receive a pop up that says the server must be demoted. click on the demote link. make sure DNS is also removed. click through the process
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