Making FreeBSD magnet links

Posted: July 3, 2018 at 4:49 PM

️ This post is old, the most up to date one is here.

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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