root-tail: 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/root-tail - from package: root-tail

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

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