actually this is not a bug. I have found the solution to this problem.
You just need to make sure that you have safely removes or eject all the removable drives (USB falsh disk, External Harddisk, etc) before shutting down. Because linux still reads it.
Mouse and external CD/DVD room doesn't have problems.
This way the message ( linux name : xxx tty1 modemmanager(805): caught signal (15)) won't show up at all.
So you don't need to edit conf, remove modemmanager or anything at all.
actually this is not a bug. I have found the solution to this problem.
You just need to make sure that you have safely removes or eject all the removable drives (USB falsh disk, External Harddisk, etc) before shutting down. Because linux still reads it.
Mouse and external CD/DVD room doesn't have problems.
This way the message ( linux name : xxx tty1 modemmanager(805): caught signal (15)) won't show up at all.
So you don't need to edit conf, remove modemmanager or anything at all.