setupadmin
Members of the setupadmin fixed server role can add and remove linked servers, and also execute some system stored procedures.
See Also
Reference
Concepts
Permissions of Fixed Server Roles
Other Resources
sp_helpsrvrole (Transact-SQL)
sp_helpsrvrolemember (Transact-SQL)
sp_srvrolepermission (Transact-SQL)
Security Considerations for Databases and Database Applications