How system get system field sy-uname ?
I check system parameter ID , found user name is put in XUS .
I use set parameter id command to change it , it can be changed.
But i run report , use debug mode , list sy-uname , it is still the login user account.
Could someone tell me how system get sy-uname ? Does it get from system parameter id ? If yes , which parameter id keeps it ?
It is not getting from any system id parameters. You cannot and should not change any sy field contents.