updatejail: 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
/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/sbin/updatejail - from package: jailer

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