idevicediagnostics: 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/idevicediagnostics - from package: libimobiledevice-utils

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

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