I've installed an UBUNTU on VirtualBox at my PC. I created a folder, linux-share, at my PC as communication area between PC & Ubuntu over VirtualBox. I found a folder sh_linux-share under Ubuntu's /media folder. sf_linux-share is obviously mirror of linux-share. I copied Linux kernel source folder into linux-share and then I found it inside Ubuntu's /media/sf_linux-share.
Then I found some phenomenon strange at LEAST for a Ubuntu's new COMER like me. I get used to Linux distributions other than Ubuntu.
I tried to 'cd' to sh_linux-share from /media. I replied me 'permission denied'. When I prefixed the command by 'sudo', it replied me "sudo: cd: command not found". I tried to copy a folder L3.0.0.35.* under /media/sf_linux-share to another place. It replied me 'cp: omitting directory 'sf_linux-share/L3.0.0.35.*'.
Please see attached file to see the dialog process more clearly.
How come? Could anyone tell me? BTW, any way to get used to Ubuntu quickly for a experienced non-Ubuntu user? Thanks.

[recovering disk space, attachment DELETED by admin]You need to be a member of the vboxsf group. I had this problem and fixed it using system settings to add myself to the group. Reboot afterwards so that the computer re-reads the group members.I worked it by using 'su -' to CHANGE myself to 'root' and then execute that 'cp' again.