about linux command
 

Hi,everyone!I have a question to know ,please help me!
if i back to up level menu ,i will type "cd ..",but if i will back to ROOT menu ,what can i do?not "cd .. ".

that makes very little sense, please describe your question in more detail. you appear to be asking how to go back one level from the root (/) directory. that's not possible as it is the root of the directroy structure.

'cd /' will take you straight to the ROOT level. One advice, get acquainted with 'absolute path' and 'relative path' definitions. In short with linux, An absoute path is any path that starts with a / for eg. /home , /usr/local/src and a relative path is one that is pertinent only from your current working directory for eg. if you are inside /home/user a ../../usr/local/src is also a valid relative path.