dia-normal: 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/dia-normal - from package: dia

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

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