ibdiagui: 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/ibdiagui - from package: ibutils

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

On Debian possible default full paths are:

/usr/bin/ibdiagui - from package: ibutils

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

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