The libyang library can be installed from third-party packages available here.
Note: the libyang dev/devel packages need to be installed in addition to the libyang core package in order to build FRR successfully.
Warning
libyang ABI version 0.16.74 or newer will be required to build FRR in the near future since it significantly eases build and installation considerations. "0.16-r3" is equal to 0.16.105 and will work, "0.16-r2" is equal to 0.16.52 and will stop working. The CI artifacts will be updated shortly.
For example, for CentOS 7.x:
wget https://ci1.netdef.org/artifact/LIBYANG-YANGRELEASE/shared/build-1/CentOS-7-x86_64-Packages/libyang-0.16.46-0.x86_64.rpm wget https://ci1.netdef.org/artifact/LIBYANG-YANGRELEASE/shared/build-1/CentOS-7-x86_64-Packages/libyang-devel-0.16.46-0.x86_64.rpm sudo rpm -i libyang-0.16.46-0.x86_64.rpm libyang-devel-0.16.46-0.x86_64.rpm
or Ubuntu 18.04:
wget https://ci1.netdef.org/artifact/LIBYANG-YANGRELEASE/shared/build-1/Ubuntu-18.04-x86_64-Packages/libyang-dev_0.16.46_amd64.deb wget https://ci1.netdef.org/artifact/LIBYANG-YANGRELEASE/shared/build-1/Ubuntu-18.04-x86_64-Packages/libyang_0.16.46_amd64.deb sudo apt install libpcre3-dev sudo dpkg -i libyang-dev_0.16.46_amd64.deb libyang_0.16.46_amd64.deb
Note
For Debian-based systems, the official libyang package requires recent versions of swig (3.0.12) and debhelper (11) which are only available in Debian buster (10). However, libyang packages built on Debian buster can be installed on both Debian jessie (8) and Debian stretch (9), as well as various Ubuntu systems. The python3-yang package will not work, but the other packages (libyang-dev is the one needed for FRR) will.
Alternatively, libyang can be built and installed manually by following the steps below:
git clone https://github.com/opensourcerouting/libyang cd libyang git checkout -b tmp origin/tmp mkdir build; cd build cmake -DENABLE_LYD_PRIV=ON .. make sudo make install
When building libyang on CentOS 6, it's also necessary to pass the
-DENABLE_CACHE=OFF parameter to cmake.
Note: please check the libyang build requirements first.