William Takeda's Profile

The & is an important little character in UNIX; it means "run
the command in the background"; i.e., detach it from the window it was started
from, so it does not block the command line.

Should the program ever try to read from the terminal window, it will be
suspended, until the user "brings it to the foreground"; i.e., brings it
to the state it would have had without the & to begin with.

To bring a program to the foreground, use "fg" or "%". If you
have more than one background job to choose from ("jobs" will show you),
then use for example "%2" to choose the second one.

Important:

If you forget to give the & at the end of line, and the process blocks
the command input to the terminal window, you can put the process in the
background "after the fact", by using Ctrl-Z. The process is suspended,
and you get the command prompt back. The first thing you should do then is
probably to give the command "bg", that resumes the process, but now in the
background.