What flag sets the block size when using the tar command?

The flag that sets the block size when using the tar command is indeed the option that specifies the block size in 512-byte records. When you use the -b flag, you can define how many blocks of data are read and written at a time. This can be particularly useful when dealing with large files or when performance is a factor, as adjusting the block size can influence the speed of the backup or extraction processes.

The other options do serve different purposes in the tar command. For instance, the -c flag is used to create a new archive, which doesn’t relate to block size settings. The -f flag is employed to specify the filename of the archive you are working with. The -x flag is for extracting files from an archive. Thus, while each of these flags holds significance for the tar command, the -b flag is the specialized option designed explicitly for setting the block size.