Making FreeBSD magnet links

Posted: July 3, 2018 at 4:49 PM

For the last few years, I’ve been producing torrents and publishing magnet links, but there is some special work that I do to make these. The first few releases, I inserted a bogus tracker into the torrent, because despite there being plenty of tools out there for producing trackerless (DHT) torrents, they were all GUI and I never found any that were command line based. The other was there was/is no tool for extracting the info hash and building the magnet link. There may be tools now, but I couldn’t find any when I started 3 years ago.

The following steps are based upon the recent release of FreeBSD 11.2‑R, adjust as necessary.

  1. Fetch FreeBSD into a directory (I create a per release directory). There are a few directories that you have mirror, I use wget for this. The mirroring feature for wget isn’t great. After each command I have to remove the CHECKSUM.SHA256, CHECKSUM.SHA512 and index.html* files.
       $ wget -c -r -l 1 -nd --limit-rate=800k
       $ wget -c -r -l 1 -nd --limit-rate=800k
       $ wget -c -r -l 1 -nd --limit-rate=800k
       $ wget -c -r -l 1 -nd --limit-rate=800k
  2. Fetch the signature files:
       $ wget{amd64,i386,powerpc,powerpc-powerpc64,sparc64,arm64-aarch64}.asc
       $ wget{amd64,i386,arm64-aarch64}-vm.asc
  3. Verify the GPG key that signed the above files. This is usually Glen Barber’s key, but not always. I have met and verified his fingerprint in person, If you have verified someone’s key who has signed Glen’s key, that is another good way.
  4. Verify the checksum files:
       $ for i in *.asc; do gpg --verify $i; done
       You should see a bunch of lines like:
       Warning: using insecure memory!
       gpg: Signature made Fri Jun 22 09:33:50 2018 PDT
       gpg:                using RSA key 0x031458A5478FE293
       gpg: Good signature from "Glen Barber <>" [full]
       gpg:                 aka "Glen Barber <>" [full]
       gpg:                 aka "Glen Barber <>" [full]
       gpg:                 aka "Glen Barber <>" [unknown]
       gpg: WARNING: not a detached signature; file 'CHECKSUM.SHA512-FreeBSD-11.2-RELEASE-amd64-vm' was NOT verified!
    The last line can be ignored. The non-.asc files were d/l’d and will not be used. Make sure that all of the files report Good signature.
  5. In the past I have used BitTornado for other things, so I ended up using it as the basis to make the tool for creating trackerless torrent files. The modifications were simple. It appears that the original BitTornado CVS tree is off-line (anyways, it was served insecurely), but it looks like effigies/BitTornado is similar enough that it could be modified and used. I copied to and applied the following patch:
       $ diff -u 
       ---   2004-05-24 12:54:52.000000000 -0700
       +++        2016-10-10 17:13:32.742081000 -0700
       @@ -23,9 +23,9 @@
        def prog(amount):
            print '%.1f%% complete\r' % (amount * 100),
       -if len(argv) < 3:
       +if len(argv) < 2:
            a,b = split(argv[0])
       -    print 'Usage: ' + b + ' <trackerurl> <file> [file...] [params...]'
       +    print 'Usage: ' + b + ' <file> [file...] [params...]'
            print formatDefinitions(defaults, 80)
       @@ -33,9 +33,9 @@
       -    config, args = parseargs(argv[1:], defaults, 2, None)
       -    for file in args[1:]:
       -        make_meta_file(file, args[0], config, progress = prog)
       +    config, args = parseargs(argv[1:], defaults, 1, None)
       +    for file in args[0:]:
       +        make_meta_file(file, None, config, progress = prog)
        except ValueError, e:
            print 'error: ' + str(e)
            print 'run with no args for parameter explanations'
    If you notice, the only thing that is done is to drop the first argument, and instead of passing it into make_meta_file, a None is passed instead. This will simply not add trackers to the torrent file.
  6. I then run the following script to verify the downloaded files, and generate the torrent files:
       $ cat 
       #!/bin/sh -
       # wget -c -r -l 1 -nd --limit-rate=800k
       # wget -c -r -l 1 -nd --limit-rate=800k
       # wget -c -r -l 1 -nd --limit-rate=800k
       # wget -c -r -l 1 -nd --limit-rate=800k
       # wget{amd64,i386,powerpc,powerpc-powerpc64,sparc64,arm64-aarch64}.asc
       # wget{amd64,i386,arm64-aarch64}-vm.asc
       grep -h '^SHA512' CHECK*.asc | sed -e 's/SHA512 (\(.*\)) = \(.*\)/\2 \1/' | sort -k 2 > sha512.from.asc
       while read hash fname; do
               if [ -e "$fname" ]; then
                       sigfile=`grep -l -- "$fname" *.asc | head -n 1`
                       echo checking "$fname", sig in: "$sigfile"
                       #res=`sha512 -q "$fname"`
                       res=`shasum -a 512 "$fname" | awk '{ print $1 }'`
                       echo "File is: $res"
                       if [ x"$res" != x"$hash" ]; then
                               echo missmatch!  "$fname"
                               exit 1
                       if ! [ -e "$fname".torrent ]; then
                       echo missing "$fname"
                       exit 1
       done < sha512.from.asc
  7. Once all the torrents have been generated, I then make the magnet links:
       $ cat 
       #!/bin/sh -
       # metainfo file.: FreeBSD-10.3-RELEASE-sparc64-bootonly.iso.torrent
       # info hash.....: 06091dabce1296d11d1758ffd071e7109a92934f
       # file name.....: FreeBSD-10.3-RELEASE-sparc64-bootonly.iso
       # file size.....: 203161600 (775 * 262144 + 0)
       # announce url..: udp://
       # btshowmetainfo 20030621 - decode BitTorrent metainfo files
       for i in *.torrent; do
      "$i" | awk '
       $0 ~ "^info hash" { info = $3 }
       $0 ~ "^file name" { name = $3 }
       END {
               print "magnet:?xt=urn:btih:" info "&dn=" name
  8. I then create the magnet links file, and update the Torrents wiki page.

Sorry about the code formatting. I don’t know how to make it look better in blogger.This blog no longer uses blogger.

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