tau_convert: 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/tau_convert - from package: tau
/usr/lib/tau/x86_64/bin/tau_convert - from package: tau

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

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