If you are taking Magento2 [Files + Database] from server & setup on localhost & while trying to open Admin , It will be not opened, due to cookie domain values specified for a particular domain name.
Solution: There are following below command need to ben run
[1]-: Run select query , to check how many cookie domain values are present in Database
select * from core_config_data
WHERE path = "web/cookie/cookie_domain"
[2]-: Run update query:
To update all path = “web/cookie/cookie_domain” into 0
update core_config_data
set value="0"
WHERE path = "web/cookie/cookie_domain"Once run query all path = “web/cookie/cookie_domain” values will be converted into 0, check again by using select query
select * from core_config_data
WHERE path = "web/cookie/cookie_domain"
Note: Here only one cookie domain value, if some cases multi store, there are multiple path = "web/cookie/cookie_domain" & each path value having domain name exists, so you need to converts all path = "web/cookie/cookie_domain" values into 0
Finally, localhost Magento 2 admin issue has been resolved.