db2index-online: 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/sbin/db2index-online - from package: 389-ds-base

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

Error in other languages:
db2index-online: bevel nie gevind nie
db2index-online: comandă negăsită
db2index-online: comando não encontrado
db2index-online: commande introuvable
db2index-online: command not found
db2index-online: käsku ei ole
db2index-online: không tìm thấy lệnh
db2index-online: komanda nerasta
db2index-online: Kommando nicht gefunden.
db2index-online: kommandot finns inte
db2index-online: komut yok
db2index-online: nie znaleziono polecenia
db2index-online: níor aimsíodh an t-ordú
db2index-online: no se encontró la orden
db2index-online: no s'ha trobat l'ordre
db2index-online: opdracht niet gevonden
db2index-online: parancs nem található
db2index-online: perintah tidak ditemukan
db2index-online: príkaz nenájdený
db2index-online: příkaz nenalezen
db2index-online: команда не найдена
db2index-online: командата не е открита
db2index-online: 命令找不到
db2index-online: コマンドが見つかりません