linux - Who try to access root@ -

i couldn't find how can have list of ip try access root@ (it command in linux couldn't find it). , how can block ip access.

there try access root@ on server. need resolve problem.

i tried don't work :

cat access.log| awk '{print $1}' | sort | uniq -c |sort -n 

just type:

last root  

this give details of ip addresses of machines users logged in root.