logging on as su and loggin on as su - ???

Why a possibly silly question - In a post on another forum I was told that it was important to log on as su - to start my adsl connection.

Any obvious differences between the two???

Thanks

su -
puts you in the root environment (esp important here as the command to start adsl is probably in the PATH setup for root).

su
gives you root but still with the user environmental settings.

If you use su you will retain the evironment of the user you su'd from, i.e. home directory, PATH, etc.

If you use su - you will have the environment of the user you su'd to.

That explains it all. Thanks.

Google brought be here.
So what would be advisable when I need to switch to admin mode for installation ? su or su - ?

I'd say "su -". Both should work though.

Basically, when you are installing something and you need to run ie "make install" as root,
one of the things it does is copy the compiled application (compiled and linked via "make" typically) to
standard paths like /bin, /usr/bin, etc.
However, those directories are readable/searchable by everyone (so anyone can use the utils), but they're only writable by root (thus making root privilege necessary for installing stuff).
Changing these permissions to make the directories writable is a serious security hazard.

However, your environment settings probably don't play a role when "make install" is copying programs into
/bin, etc (cp only needs to be run under root user to have the write access).