mpirun_dbg.ddd: command not found

Have You tried accessing the binary with the full path?

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/lib64/mvapich-psm/bin/mpirun_dbg.ddd - from package: mvapich-psm
/usr/lib64/mvapich/bin/mpirun_dbg.ddd - from package: mvapich
/usr/lib/mvapich/bin/mpirun_dbg.ddd - from package: mvapich

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