runuser: 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/runuser - from package: coreutils

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

On Debian possible default full paths are:

/sbin/runuser - from package: util-linux

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

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