zfs: 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/zfs - from package: zfs-fuse

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

On Debian possible default full paths are:

/sbin/zfs - from package: zfs-fuse

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

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