zsh4: 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:

/bin/zsh4 - from package: zsh

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

Error in other languages:
zsh4: bevel nie gevind nie
zsh4: comandă negăsită
zsh4: comando não encontrado
zsh4: commande introuvable
zsh4: command not found
zsh4: käsku ei ole
zsh4: không tìm thấy lệnh
zsh4: komanda nerasta
zsh4: Kommando nicht gefunden.
zsh4: kommandot finns inte
zsh4: komut yok
zsh4: nie znaleziono polecenia
zsh4: níor aimsíodh an t-ordú
zsh4: no se encontró la orden
zsh4: no s'ha trobat l'ordre
zsh4: opdracht niet gevonden
zsh4: parancs nem található
zsh4: perintah tidak ditemukan
zsh4: príkaz nenájdený
zsh4: příkaz nenalezen
zsh4: команда не найдена
zsh4: командата не е открита
zsh4: 命令找不到
zsh4: コマンドが見つかりません