clang-tidy: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/lib/llvm-3.4/bin/clang-tidy - from package: clang-3.4
/usr/lib/llvm-3.5/bin/clang-tidy - from package: clang-3.5
/usr/bin/clang-tidy - from package: clang

You may install the required package with command apt-get install {package}

Error in other languages:
clang-tidy: bevel nie gevind nie
clang-tidy: comandă negăsită
clang-tidy: comando não encontrado
clang-tidy: commande introuvable
clang-tidy: command not found
clang-tidy: käsku ei ole
clang-tidy: không tìm thấy lệnh
clang-tidy: komanda nerasta
clang-tidy: Kommando nicht gefunden.
clang-tidy: kommandot finns inte
clang-tidy: komut yok
clang-tidy: nie znaleziono polecenia
clang-tidy: níor aimsíodh an t-ordú
clang-tidy: no se encontró la orden
clang-tidy: no s'ha trobat l'ordre
clang-tidy: opdracht niet gevonden
clang-tidy: parancs nem található
clang-tidy: perintah tidak ditemukan
clang-tidy: príkaz nenájdený
clang-tidy: příkaz nenalezen
clang-tidy: команда не найдена
clang-tidy: командата не е открита
clang-tidy: 命令找不到
clang-tidy: コマンドが見つかりません