rootsh: 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:

/usr/bin/rootsh - from package: rootsh

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

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