dbscan: 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/dbscan - from package: 389-ds-base

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

On Debian possible default full paths are:

/usr/bin/dbscan - from package: 389-ds-base

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

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