Just stop already, you don't know what you're talking about. ps works just fine. The jail itself picks up the version of the host because it's calling the newer kernel, but otherwise works as one would expect. In fact it's probably worth noting that between 10 and 12 the libc major version wasn't even bumped. For all the bellyaching you're missing that each major version is supported for five years, and that unlike RHEL you'll get up-to-date ports with that (instead of the half-assed cobbled together ancient versions that linger with the RHEL model) so there's less incentive to upgrade until you're ready. That's a lot of hand waving over a non fucking issue.

If you were making a more earnest argument you'd probably have looked at the current version of the documentation and noted that it doesn't have the warning you quoted.

https://docs.freebsd.org/en/books/handbook/kernelconfig/#ker...

Note that FreeBSD 10.0 was released in January 2014, over nine years ago. 10.4, which is the oldest base jail image I have kicking around, was released in 2017. So the userland-kernel interfaces you're wringing your hands over have remained stable for nearly a decade across three or four different major releases.

Of all the concerns I'd have about running FreeBSD and/or jails in a prod environment, dealing with binary compatibility across different major versions is not even on my radar and not even remotely an advantage for docker.

  # uname -rv
  12.4-RELEASE-p1 FreeBSD 12.4-RELEASE-p1 GENERIC
  # ldd /bin/ps
  /bin/ps:
          libm.so.5 => /lib/libm.so.5 (0x800254000)
          libkvm.so.7 => /lib/libkvm.so.7 (0x80028b000)
          libjail.so.1 => /lib/libjail.so.1 (0x80029e000)
          libxo.so.0 => /lib/libxo.so.0 (0x8002a6000)
          libc.so.7 => /lib/libc.so.7 (0x8002c5000)
          libelf.so.2 => /lib/libelf.so.2 (0x8006b9000)
          libutil.so.9 => /lib/libutil.so.9 (0x8006d4000)
  # md5sum /bin/ps
  ad8b5c8966c71e31cdc9603967860fa7  /bin/ps
  # objdump -p /lib/libc.so.7 | tail -12
  
  Version definitions:
  1 0x01 0x0865f4e7 libc.so.7
  2 0x00 0x077a28b0 FBSD_1.0
  3 0x00 0x077a28b1 FBSD_1.1
  4 0x00 0x077a28b2 FBSD_1.2
  5 0x00 0x077a28b3 FBSD_1.3
  6 0x00 0x077a28b4 FBSD_1.4
  7 0x00 0x077a28b5 FBSD_1.5
  8 0x00 0x077a28b6 FBSD_1.6
  9 0x00 0x0f1efaa0 FBSDprivate_1.0
  
  # iocage create -r 10.4-RELEASE
  e950694e-6182-410d-bc70-1a8f6e340516 successfully created!
  # iocage start e950694e-6182-410d-bc70-1a8f6e340516
  * Starting e950694e-6182-410d-bc70-1a8f6e340516
    + Started OK
    + Using devfs_ruleset: 1007 (iocage generated default)
    + Using IP options: ip4.saddrsel=1 ip4=new ip6.saddrsel=1 ip6=new
    + Starting services OK
    + Executing poststart OK
  # iocage console e950694e-6182-410d-bc70-1a8f6e340516
  FreeBSD 12.4-RELEASE-p1 GENERIC
  
  Welcome to FreeBSD!
  
  Release Notes, Errata: https://www.FreeBSD.org/releases/
  Security Advisories:   https://www.FreeBSD.org/security/
  FreeBSD Handbook:      https://www.FreeBSD.org/handbook/
  FreeBSD FAQ:           https://www.FreeBSD.org/faq/
  Questions List: https://lists.FreeBSD.org/mailman/listinfo/freebsd-questions/
  FreeBSD Forums:        https://forums.FreeBSD.org/

  Documents installed with the system are in the /usr/local/share/doc/freebsd/
  directory, or can be installed later with:  pkg install en-freebsd-doc
  For other languages, replace "en" with a language code like de or fr.

  Show the version of FreeBSD installed:  freebsd-version ; uname -a
  Please include that output and any error messages when posting questions.
  Introduction to manual pages:  man man
  FreeBSD directory layout:      man hier
  
  Edit /etc/motd to change this login announcement.
  # ldd /bin/ps
  /bin/ps:
          libm.so.5 => /lib/libm.so.5 (0x800827000)
          libkvm.so.6 => /lib/libkvm.so.6 (0x800a50000)
          libjail.so.1 => /lib/libjail.so.1 (0x800c59000)
          libc.so.7 => /lib/libc.so.7 (0x800e5e000)
  # objdump -p /lib/libc.so.7 | tail -16
  Version definitions:
  1 0x01 0x0865f4e7 libc.so.7
  2 0x00 0x077a28b0 FBSD_1.0
  3 0x00 0x077a28b1 FBSD_1.1
          FBSD_1.0
  4 0x00 0x077a28b2 FBSD_1.2
          FBSD_1.1
  5 0x00 0x077a28b3 FBSD_1.3
          FBSD_1.2
  6 0x00 0x077a28b4 FBSD_1.4
          FBSD_1.3
  7 0x00 0x077a28b5 FBSD_1.5
          FBSD_1.4
  8 0x00 0x0f1efaa0 FBSDprivate_1.0
          FBSD_1.5
  
  # md5 /bin/ps
  MD5 (/bin/ps) = 8a9c364705d29beb98503415428067cc
  # ps
    PID TT  STAT    TIME COMMAND
  80454 39  IJ   0:00.01 login [pam] (login)
  80455 39  SJ   0:00.03 -csh (csh)
  80593 39  R+J  0:00.00 ps