zsh-beta: 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/zsh-beta - from package: zsh-beta

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

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