clusterdb: 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/bin/clusterdb - from package: postgresql

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

On Debian possible default full paths are:

/usr/bin/clusterdb - from package: postgresql-client-common
/usr/lib/postgresql/9.4/bin/clusterdb - from package: postgresql-client-9.4

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

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