$ sudo apt build-dep rsync
$ sudo apt install libxxhash-dev libzstd-dev liblz4-dev
$ wget -c \
https://download.samba.org/pub/rsync/rsync-3.2.0.tar.gz \
https://download.samba.org/pub/rsync/rsync-3.2.0.tar.gz.asc \
https://opencoder.net/WayneDavison.key
$ gpg2 --import ./WayneDavison.key
$ gpg2 --verify ./rsync-3.2.0.tar.gz.asc
$ tar tvzf ./rsync-3.2.0.tar.gz
$ tar xzf ./rsync-3.2.0.tar.gz
$ cd rsync-3.2.0
$ ./configure --help
$ ./configure
$ make
$ ./rsync --version
rsync  version 3.2.0  protocol version 31
Copyright (C) 1996-2020 by Andrew Tridgell, Wayne Davison, and others.
Web site: http://rsync.samba.org/
Capabilities:
    64-bit files, 64-bit inums, 64-bit timestamps, 64-bit long ints,
    socketpairs, hardlinks, symlinks, IPv6, batchfiles, inplace, append,
    ACLs, xattrs, iconv, symtimes, prealloc, SIMD
Checksum list:
    xxh64 (xxhash) md5 md4 none
Compress list:
    zstd lz4 zlibx zlib none

rsync comes with ABSOLUTELY NO WARRANTY.  This is free software, and you
are welcome to redistribute it under certain conditions.  See the GNU
General Public Licence for details.

$ make
  :
token.c: In function ‘init_compression_level’:
token.c:73:40: warning: implicit declaration of function ‘ZSTD_minCLevel’; did you mean ‘ZSTD_maxCLevel’? [-Wimplicit-function-declaration]
   min_level = skip_compression_level = ZSTD_minCLevel();
                                        ^~~~~~~~~~~~~~
                                        ZSTD_maxCLevel
token.c: In function ‘send_zstd_token’:
token.c:685:2: error: unknown type name ‘ZSTD_EndDirective’; did you mean ‘ZSTD_DDict’?
  ZSTD_EndDirective flush = ZSTD_e_continue;
  ^~~~~~~~~~~~~~~~~
  ZSTD_DDict
token.c:685:28: error: ‘ZSTD_e_continue’ undeclared (first use in this function)
  ZSTD_EndDirective flush = ZSTD_e_continue;
                            ^~~~~~~~~~~~~~~
token.c:685:28: note: each undeclared identifier is reported only once for each function it appears in
token.c:701:3: warning: implicit declaration of function ‘ZSTD_CCtx_setParameter’ [-Wimplicit-function-declaration]
   ZSTD_CCtx_setParameter(zstd_cctx, ZSTD_c_compressionLevel, do_compression_level);
   ^~~~~~~~~~~~~~~~~~~~~~
token.c:701:37: error: ‘ZSTD_c_compressionLevel’ undeclared (first use in this function); did you mean ‘skip_compression_level’?
   ZSTD_CCtx_setParameter(zstd_cctx, ZSTD_c_compressionLevel, do_compression_level);
                                     ^~~~~~~~~~~~~~~~~~~~~~~
                                     skip_compression_level
token.c:751:13: error: ‘ZSTD_e_flush’ undeclared (first use in this function); did you mean ‘ZSTD_DCtx_s’?
     flush = ZSTD_e_flush;
             ^~~~~~~~~~~~
             ZSTD_DCtx_s
token.c:753:8: warning: implicit declaration of function ‘ZSTD_compressStream2’; did you mean ‘ZSTD_compressStream’? [-Wimplicit-function-declaration]
    r = ZSTD_compressStream2(zstd_cctx, &zstd_out_buff, &zstd_in_buff, flush);
        ^~~~~~~~~~~~~~~~~~~~
        ZSTD_compressStream
$ cd ..
$ sudo apt remove libzstd-dev
$ wget https://github.com/facebook/zstd/releases/download/v1.4.5/zstd-1.4.5.tar.gz \
https://github.com/facebook/zstd/releases/download/v1.4.5/zstd-1.4.5.tar.gz.sha256
$ sha256sum -c ./zstd-1.4.5.tar.gz.sha256
$ tar tvf ./zstd-1.4.5.tar.gz | lv
$ tar xf ./zstd-1.4.5.tar.gz
$ cd zstd-1.4.5
$ make
$ sudo make install
$ cd ../rsync-3.2.0
$ ./configure && make

$ sudo apt install rsync
$ rsync --version
rsync  version 3.2.0  protocol version 31
Copyright (C) 1996-2020 by Andrew Tridgell, Wayne Davison, and others.
Web site: http://rsync.samba.org/
Capabilities:
    64-bit files, 64-bit inums, 64-bit timestamps, 64-bit long ints,
    socketpairs, hardlinks, symlinks, IPv6, batchfiles, inplace, append,
    ACLs, xattrs, iconv, symtimes, prealloc, SIMD
Checksum list:
    xxh64 (xxhash) md5 md4 none
Compress list:
    zstd lz4 zlibx zlib none

rsync comes with ABSOLUTELY NO WARRANTY.  This is free software, and you
are welcome to redistribute it under certain conditions.  See the GNU
General Public Licence for details.
$ dpkg-query -W rsync
rsync   3.2.0-1

$ rsync --version | grep Checksum -A1
Checksum list:
    xxh64 (xxhash) md5 md4 none

  --disable-xxhash        disable xxhash checksums

$ rsync --checksum-choice=xxh64 -avc ./* user@remote:/tmp/
unknown checksum name: xxh64
rsync error: requested action not supported (code 4) at checksum.c(73) [server=3.1.3]
rsync: connection unexpectedly closed (0 bytes received so far) [sender]
rsync error: error in rsync protocol data stream (code 12) at io.c(235) [sender=3.2.0]

$ find ./linux-5.6 | wc -l
82114
$ du -ms ./linux-5.6
1310    ./linux-5.6
$ rsync --checksum-choice=auto -ac ./linux-5.6 /tmp/
$ sync ; echo 3 | sudo tee /proc/sys/vm/drop_caches ; time rsync --checksum-choice=md4 -ac ./linux-5.6 /tmp/
3

real    0m52.393s
user    0m5.051s
sys     0m12.246s

$ sync ; echo 3 | sudo tee /proc/sys/vm/drop_caches ; time rsync --checksum-choice=md5 -ac ./linux-5.6 /tmp/
3

real    0m57.716s
user    0m6.976s
sys     0m13.486s

$ sync ; echo 3 | sudo tee /proc/sys/vm/drop_caches ; time rsync --checksum-choice=xxh64 -ac ./linux-5.6 /tmp/
3

real    1m5.520s
user    0m2.507s
sys     0m13.625s

$ ls -s ./Parrot-security-4.9.1_x64.iso*
3909164 ./Parrot-security-4.9.1_x64.iso  3909164 ./Parrot-security-4.9.1_x64.iso2
$ sync ; echo 3 | sudo tee /proc/sys/vm/drop_caches ; time rsync --checksum-choice=md4 -ac ./Parrot-security-4.9.1_x64.iso ./Parrot-security-4.9.1_x
64.iso2
3

real    0m23.276s
user    0m10.601s
sys     0m4.387s

$ sync ; echo 3 | sudo tee /proc/sys/vm/drop_caches ; time rsync --checksum-choice=md5 -ac ./Parrot-security-4.9.1_x64.iso ./Parrot-security-4.9.1_x64.iso2
3

real    0m28.150s
user    0m16.945s
sys     0m4.399s

$ sync ; echo 3 | sudo tee /proc/sys/vm/drop_caches ; time rsync --checksum-choice=xxh64 -ac ./Parrot-security-4.9.1_x64.iso ./Parrot-security-4.9.1_x64.iso2
3

real    0m12.767s
user    0m1.375s
sys     0m4.060s

$ pkill -SIGVTALRM rsync

linux-5.6/arch/sparc/lib/lshrdi3.S
    114,384,392  81%  931.12kB/s    0:01:59 (xfr#21058, ir-chk=1030/23451)

$ ls -Al /tmp/rsync-test/
total 0
-rw-r--r-- 1 matoken  matoken  0 Jun 25 18:50 matokenfile
-rw-r--r-- 1 root     root     0 Jun 25 18:51 root
-rw-r--r-- 1 www-data www-data 0 Jun 25 18:51 www-data

$ sudo ./rsync -a /tmp/rsync-test/ /tmp/rsync-test2
$ ls -lA /tmp/rsync-test2
total 0
-rw-r--r-- 1 matoken  matoken  0 Jun 25 18:50 matokenfile
-rw-r--r-- 1 root     root     0 Jun 25 18:51 root
-rw-r--r-- 1 www-data www-data 0 Jun 25 18:51 www-data

$ sudo \rm -rf /tmp/rsync-test2
$ sudo ./rsync --copy-as=matoken -a /tmp/rsync-test/ /tmp/rsync-test2
$ ls -lA /tmp/rsync-test2
total 0
-rw-r--r-- 1 matoken matoken 0 Jun 25 18:50 matokenfile
-rw-r--r-- 1 matoken matoken 0 Jun 25 18:51 root
-rw-r--r-- 1 matoken matoken 0 Jun 25 18:51 www-data

$ ./rsync --help|grep -- -V
--version, -V            print the version + other info and exit
$ ./rsync --help|grep \-V
grep (GNU grep) 3.4
Copyright (C) 2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Mike Haertel and others; see
<https://git.sv.gnu.org/cgit/grep.git/tree/AUTHORS>.

$ rsync -avc6 ./ user@remote:/tmp/
ssh: Could not resolve hostname remote: Name or service not known
rsync: connection unexpectedly closed (0 bytes received so far) [sender]
rsync error: unexplained error (code 255) at io.c(235) [sender=3.2.1]