db5-valid: 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/db5-valid - from package: publican

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

Error in other languages:
db5-valid: bevel nie gevind nie
db5-valid: comandă negăsită
db5-valid: comando não encontrado
db5-valid: commande introuvable
db5-valid: command not found
db5-valid: käsku ei ole
db5-valid: không tìm thấy lệnh
db5-valid: komanda nerasta
db5-valid: Kommando nicht gefunden.
db5-valid: kommandot finns inte
db5-valid: komut yok
db5-valid: nie znaleziono polecenia
db5-valid: níor aimsíodh an t-ordú
db5-valid: no se encontró la orden
db5-valid: no s'ha trobat l'ordre
db5-valid: opdracht niet gevonden
db5-valid: parancs nem található
db5-valid: perintah tidak ditemukan
db5-valid: príkaz nenájdený
db5-valid: příkaz nenalezen
db5-valid: команда не найдена
db5-valid: командата не е открита
db5-valid: 命令找不到
db5-valid: コマンドが見つかりません