clang: 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 CentOS possible default full paths are:

/usr/bin/clang - from package: clang

You may install the required package with command yum install {package}

On Debian possible default full paths are:

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

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

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