iwyu: command not found

Have You tried accessing the binary with the full path?

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/iwyu - from package: iwyu

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

On Debian possible default full paths are:

/usr/bin/iwyu - from package: iwyu

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