+dit(bf(-4, --ipv4) or bf(-6, --ipv6)) Tells rsync to prefer IPv4/IPv6
+when creating sockets. This only affects sockets that rsync has direct
+control over, such as the outgoing socket when directly contacting an
+rsync daemon, or the incoming sockets that an rsync daemon uses to
+listen for connections. One of these options may be required in older
+versions of Linux to work around an IPv6 bug in the kernel (if you see
+an "address already in use" error when nothing else is using the port,
+try specifying --ipv6 or --ipv4 when starting the daemon).
+
+dit(bf(--checksum-seed=NUM)) Set the MD4 checksum seed to the integer
+NUM. This 4 byte checksum seed is included in each block and file
+MD4 checksum calculation. By default the checksum seed is generated
+by the server and defaults to the current time(), or 32761 if
+bf(--write-batch) or bf(--read-batch) are specified. This option
+is used to set a specific checksum seed, which is useful for
+applications that want repeatable block and file checksums, or
+in the case where the user wants a more random checksum seed.
+Note that setting NUM to 0 causes rsync to use the default of time()
+for checksum seed. Note also that bf(--write-batch) and bf(--read-batch)
+set the checksum seed to 32761, so bf(--checksum-seed=NUM) needs to
+follow these options if you want to specify a different checksum
+seed in batch mode.
+