zkServer.sh: 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/share/zookeeper/bin/zkServer.sh - from package: zookeeper

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

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