mpirun_lam: 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/lib/petscdir/3.4.2/bin/mpirun_lam - from package: libpetsc3.4.2-dev

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

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