dh-exec: 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/bin/dh-exec - from package: dh-exec

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

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