runlevel: 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 CentOS possible default full paths are:

/sbin/runlevel - from package: upstart

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/sbin/runlevel - from package: systemd-sysv
/sbin/runlevel - from package: sysvinit-core
/sbin/runlevel - from package: upstart

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

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