I knew about USR1 and it's in the man for me too, but I don't see anything about skip_bytes / count_bytes flags, which is strange.
Debian testing, coreutils 9.1.
Debian testing, coreutils 9.1.
It is also in Coreutils 8.22 in RHEL7.
https://man7.org/linux/man-pages/man1/dd.1.html
Edit: I just found this in the coreutils 9.0 changelog:
dd now counts bytes instead of blocks if a block count ends in "B".
For example, 'dd count=100KiB' now copies 100 KiB of data, not
102,400 blocks of data. The flags count_bytes, skip_bytes and
seek_bytes are therefore obsolescent and are no longer documented,
though they still work.So you can simply do something like:
dd if=foo skip=nB count=mB bs=4M of=bar