diff_tomo: 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/diff_tomo - from package: pyfai

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

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