zsh: 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:

/bin/zsh - from package: zsh

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

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