pg_filedump is a utility to format PostgreSQL heap/index/control files into a
human-readable form. You can format/dump the files several ways, as listed in
the Invocation section, as well as dumping straight binary.

The type of file (heap/index) can usually be determined automatically by the
content of the blocks within the file. However, to format a pg_control file you
must use the -c option.

The default is to format the entire file using the block size listed in block 0
and display block relative addresses. These defaults can be modified using
run-time options.

Some options may seem strange but they're there for a reason. For example, block
size. It's there because if the header of block 0 is corrupt, you need a method
of forcing a block size.