db2ris: 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/db2ris - from package: refdb-clients

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

Error in other languages:
db2ris: bevel nie gevind nie
db2ris: comandă negăsită
db2ris: comando não encontrado
db2ris: commande introuvable
db2ris: command not found
db2ris: käsku ei ole
db2ris: không tìm thấy lệnh
db2ris: komanda nerasta
db2ris: Kommando nicht gefunden.
db2ris: kommandot finns inte
db2ris: komut yok
db2ris: nie znaleziono polecenia
db2ris: níor aimsíodh an t-ordú
db2ris: no se encontró la orden
db2ris: no s'ha trobat l'ordre
db2ris: opdracht niet gevonden
db2ris: parancs nem található
db2ris: perintah tidak ditemukan
db2ris: príkaz nenájdený
db2ris: příkaz nenalezen
db2ris: команда не найдена
db2ris: командата не е открита
db2ris: 命令找不到
db2ris: コマンドが見つかりません