We can set root password new or update of all nodes in a MemSQL cluster, replacing with your desired password. Note that this command execute is an offline operation that will result in some cluster downtime.

# memsql-ops memsql-list -q | xargs -n 1 memsql-ops memsql-update-root-password --no-confirmation -p "MemSQL-Password"

2016-10-26 12:41:09: J4258a1 [INFO] Updating root password for MemSQL node 29D77C4D6F7A124BAA504FA719EE2A3D773334BE
2016-10-26 12:41:09: J4258a1 [INFO] Successfully updated root password for MemSQL node 29D77C4D6F7A124BAA504FA719EE2A3D773334BE

You can login with below command,

# mysql -u root -h 127.0.0.1 -P 3306 --prompt="memsql>" -p

Enter password: 


Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 13
Server version: 5.5.8 MemSQL source distribution (compatible; MySQL Enterprise & MySQL Commercial)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

memsql>quit
Bye


or

Use the below commands, In MemSQL  you should use the GRANT command:


grant all on *.* to 'root'@'localhost' identified by 'password' with grant option;
grant all on *.* to 'root'@'%' identified by 'password' with grant option;


Also, refer to the manual of the GRANT command : http://docs.memsql.com/latest/ref/GRANT/