Invoking su in emacs' eshell

I can run normal linux commands in eshell as a non-root user. When I try to su to root, all the usual linux commands are gone (ls, cat, etc.) How开发者_StackOverflow中文版 do I fix this?

One way is to use tramp:

cd /su::/etc/
ls

then eshell will run command "remotly" using su.

After testing, it seem that ls do work, but there is a problem with some (but not all) external command.