To create a USB flash drive using Mac OS X, so that you can boot from it and install Ubuntu on your Mac (or another machine), you have to perform administrative tasks. When you perform an administrative task with a graphical program (i.e., outside of Terminal.app), you are prompted for your password. You've almost certainly seen this before--when you install certain software, or when you install updates or modify global settings in System Preferences, you're prompted for your password.
This is the same sort of thing, but in the Terminal. If you want to proceed and perform the task in your command, you'll enter your password (the same one you'd use to log on to your Mac OS X system or to perform any of those administrative tasks graphically as discussed above). As you enter it, you won't see any placeholder characters (like
*). That's by design. Just put it in and press Enter.
sudo will work essentially the same way in your Ubuntu system as well. (And like in Mac OS X, in Ubuntu most likely you'll be performing most administrative tasks graphically, so you'll get graphical password prompts like you do most of the time in Mac OS X.)
You should understand what
sudo does and why that warning is displayed before proceeding, though.
This message appears normally, the first time you use
sudo, on some versions of Mac OS X (and maybe some other OSes too):
WARNING: Improper use of the sudo command could lead to data loss
or the deletion of important system files. Please double-check your
typing when using sudo. Type "man sudo" for more information.
To proceed, enter your password, or type Ctrl-C to abort.
It is not, in and of itself, anything to worry about. It's just warning you that
sudo is very powerful, and that you can do just about anything with it...including things that you do not want to do and that would prevent your Mac OS X system, or other systems, from booting up until repaired or reinstalled. You could also accidentally wipe out important files such as your documents.
That warning is not in response to the particular commmand you are running. It could have been
sudo ls and you would still have seen it.
However, it turns out that particular command is especially dangerous if done wrong. What you're doing with that command is to write the data from the file specified after
if= (the input file) to the device specified after
of= (the output "file").
This will overwrite whatever data currently exist on
of= (if any), and it's unlikely you could get those data back again. Unless, of course, you have a copy somewhere else.
So not only is it important you're not overwriting valuable data...but it is also important that you specify the correct output device, or you could overwrite another device altogether (perhaps an important hard disk).
- I once typed in a
sudo dd ... command, check to make sure the device was correctly specified and that the device didn't contain any important information, ran it ...and then less than a second later realized that the command prompt I used was actually a remote login to a different computer! I cancelled it immediately, but even the small amount I did overwrite made it so the partition wouldn't be mountable again, and required me to copy the data off to another disk and consult my partial backup. And the main factor that saved me was excellent luck.
You're not likely to be making that specific error, but just make sure the command is correct, the device is correct, and there's no data you want to keep that is stored on the device.
Please note that any
sudo command is potentially dangerous if you make a mistake but
dd commands tend to be just about the most dangerous if you make a mistake. You shouldn't be reluctant to explore and experiment on either your Mac OS X or your Ubuntu system...just be careful.
I highly recommend reading Ubuntu's community documentation on
sudo to understand how it works and what to keep in mind while using it. As many of the same considerations were taken by Apple developers when they decided how to set up
sudo in Mac OS X, and because
sudo is a standard command, with all OS-specific variants changing very little (if anything) from Todd C. Miller's upstream code, most of the information there applies to Mac OS X and other OSes, as well as to the Ubuntu system you're about to install.