grub-install: 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/grub-install - from package: grub

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

On Debian possible default full paths are:

/usr/sbin/grub-install - from package: grub2-common
/usr/sbin/grub-install - from package: grub-legacy

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

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