restart: 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/restart - from package: upstart

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

On Debian possible default full paths are:

/sbin/restart - from package: upstart
/usr/lib/fastdnaml/bin/restart - from package: fastdnaml

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

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