Install File by running the following commands:
./configure --prefix=/usr --datadir=/usr/share/misc &&
make &&
make install
File uses magic numbers to determine a file type. These magic numbers come with File in a plain text file. File internally compiles this database each time it is run. This is not the normal type of operation for File since compiling a plain text file each time is not the fastest way to do it. File offers an option "-C" to compile this magic number file. The reason this isn't done automatically is that some people like to work on the magic numbers. On the other hand many people didn't get it that they should compile the magic numbers, so the author of File added a warning when the plain text magic file is used. As we usually won't work on the plain text magic file, we compile this file, because it's faster, fixes that annoying warning and is how it was meant to be:
file -C
The File package contains the file program.
File tests each specified file in an attempt to classify it. There are three sets of tests, performed in this order: filesystem tests, magic number tests, and language tests. The first test that succeeds causes the file type to be printed.