hibernate: 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 Debian possible default full paths are:

/usr/sbin/hibernate - from package: hibernate

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

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