dtdiff: 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/dtdiff - from package: dtc

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

On Debian possible default full paths are:

/usr/bin/dtdiff - from package: device-tree-compiler

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

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