redis-server: 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:

/usr/sbin/redis-server - from package: redis

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

On Debian possible default full paths are:

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

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

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