redis-sentinel: 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/bin/redis-sentinel - from package: redis-server

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

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