pivot_root: 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/pivot_root - from package: util-linux-ng

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

On Debian possible default full paths are:

/sbin/pivot_root - from package: util-linux
/usr/lib/klibc/bin/pivot_root - from package: klibc-utils

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

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