ctail: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/ctail - from package: byobu

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