Bash and other modern shell provides I/O redirection facility. There are 3 default standard files (standard streams) open:
[a] stdin - Use to get input (keyboard) i.e. data going into a program.
[b] stdout - Use to write information (screen)
[c] stderr - Use to write error message (screen)

Understanding I/O streams numbers

The Unix / Linux standard I/O streams with numbers:

Handle	Name	Description
0	stdin	Standard input
1	stdout	Standard output
2	stderr	Standard error

$ 

cat food 2>&1 >file


cat: can't open food
$ 

cat food >file 2>&1


$

Although lots of sh manual pages don't mention this, the shell reads arguments from left to right.

1. On the first command line, the shell sees 2>&1 first. That means "make the standard error (file descriptor 2) go to the same place as the standard output (fd1) is going." There's no effect because both fd2 and fd1 are already going to the terminal. Then >file redirects fd1 ( stdout ) to file . But fd2 ( stderr ) is still going to the terminal.
2. On the second command line, the shell sees >file first and redirects stdout to file . Next 2>&1 sends fd2 ( stderr ) to the same place fd1 is going - that's to the file. And that's what you want.