Spawning language server with cmd: `clangd` failed

Question

I have a c project and I would like to use the feature of LSP in Neovim such as gd (go to definition).

I follow each of these materials to configure LSP

• langserver.org/

  Konwing that I need to use clangd.

• nvim-lspconfig/doc/server_configurations.md#clangd and clangd.llvm.org/installation

  To install clangd on Ubuntu (18.04).

• TJ DeVries's guide,

  To configure nvim-lspconfig, being like

  require('lspconfig').clangd.setup{
    on_attach = function()
                  print("Hello C/C++!")
                end
  }
  

• clangd.llvm.org/installation#project-setup

  I use Bear to produce complile_command.json

However, I've encountered some problems.

1. Following the guide in clangd.llvm.org/installation, I execute sudo apt-get install clangd-10 to install clangd (sudo apt-get install clangd-12 will result in E: Unable to locate package clangd-12 even though I have executed sudo apt-get update). But when I want to check the version of clangd by executing clangd --version, I got Command 'clangd' not found as it is not installed yet.

2. After executing bear <my_build_command>, I got the complile_command.json. But when I open .c file in the project, I got the information: Spawning language server with cmd: clangd failed. The language server is either not installed, missing from PATH, or not executable.

--

I think the problem may result from 1. After Googleing the related information and tried to reinstall clangd, clangd --version still result in the same: Command 'clangd' not found.

Do I missing something or what? Any one can give me a help? Thanks.