Libyang3 vs libyang2 conflict with frr

phedman · November 13, 2025, 1:41pm

I am a bit puzzled about the state of the library libyang, used by frr.

The frr/package.toml at this time (2025-11-11):

scripts/package-build/frr/package.toml

a411efebe

[[packages]]
name = "libyang"
commit_id = "v3.4.2"
scm_url = "https://github.com/CESNET/libyang.git"
build_cmd = "pipx run apkg build -i && find pkg/pkgs -type f -name *.deb -exec mv -t .. {} +"

[[packages]]
name = "frr"
commit_id = "stable/10.2"
scm_url = "https://github.com/FRRouting/frr.git"
build_cmd = "sudo dpkg -i ../*.deb; dpkg-buildpackage -us -uc -tc -b -Ppkg.frr.rtrlib,pkg.frr.lua"

[dependencies]
packages = [
    "chrpath",
    "gawk",
    "install-info",
    "libcap-dev",
    "libc-ares-dev",
    "libjson-c-dev",

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…wants to check out and build libyang v3.4.2 along with frr stable/10.2

However, the corresponding VyOS x86 live build (2025-11-11) has libyang2 installed, not libyang3. This is from an actual live build 2025-11-11 x86 boot:

vyos@vyos:~$ ls -l /usr/lib/*/libyang*
lrwxrwxrwx 1 root root 17 May 4 2021 /usr/lib/x86_64-linux-gnu/libyang.so.2 -> libyang.so.2.46.3
-rw-r–r-- 1 root root 1290216 May 4 2021 /usr/lib/x86_64-linux-gnu/libyang.so.2.46.3
vyos@vyos:~$ dpkg-query -l libyang2
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-==============-============-============-==================================>
ii libyang2:amd64 2.1.148-1 amd64 parser toolkit for IETF YANG data >
vyos@vyos:~$
vyos@vyos:~$ show version | grep 2025
Version: VyOS 2025.11.11-0020-rolling
Built on: Tue 11 Nov 2025 00:20 UTC
vyos@vyos:~$

It is not possible to have libyang2 and libyang3 installed at the same time as they conflict with each other, so what is going on here?

Per Debian 12 — FRR latest documentation they want libyang 2.1.128 at this time (see their “DEB packages are available as CI artifacts here.” link), so having libyang3 (v3.4.2) in the package.toml seems suspicious.

Apachez · November 13, 2025, 5:45pm

I would guess thats because Debian 12 aka bookworm uses FRR 8.4.4 while VyOS does a custom compile of latest stable which currently seems to be FRR 10.2:

What output do you get from lets say “dpkg -l | grep -i libyang” ?

phedman · November 13, 2025, 6:54pm

As I said, FRR 10.2 from the distributors wants libyang2 (see link in original post) and the 2025-11-11 x86_64 VyOS rolling release comes with libyang2 despite the package.toml pointlessly building libyang3. See below:

vyos@vyos:~$ dpkg -l | grep libyang
ii libyang2:amd64 2.1.148-1 amd64 parser toolkit for IETF YANG data modeling - runtime
vyos@vyos:~$
vyos@vyos:~$ show version | grep 2025
Version: VyOS 2025.11.11-0020-rolling
Built on: Tue 11 Nov 2025 00:20 UTC
vyos@vyos:~$