mpirun_lam.1.gz: 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 Debian possible default full paths are:

/usr/lib/petscdir/3.4.2/bin/mpirun_lam.1.gz - from package: libpetsc3.4.2-dev

You may install the required package with command apt-get install {package}
Error in other languages:
mpirun_lam.1.gz: bevel nie gevind nie
mpirun_lam.1.gz: comandă negăsită
mpirun_lam.1.gz: comando não encontrado
mpirun_lam.1.gz: commande introuvable
mpirun_lam.1.gz: command not found
mpirun_lam.1.gz: käsku ei ole
mpirun_lam.1.gz: không tìm thấy lệnh
mpirun_lam.1.gz: komanda nerasta
mpirun_lam.1.gz: Kommando nicht gefunden.
mpirun_lam.1.gz: kommandot finns inte
mpirun_lam.1.gz: komut yok
mpirun_lam.1.gz: nie znaleziono polecenia
mpirun_lam.1.gz: níor aimsíodh an t-ordú
mpirun_lam.1.gz: no se encontró la orden
mpirun_lam.1.gz: no s'ha trobat l'ordre
mpirun_lam.1.gz: opdracht niet gevonden
mpirun_lam.1.gz: parancs nem található
mpirun_lam.1.gz: perintah tidak ditemukan
mpirun_lam.1.gz: príkaz nenájdený
mpirun_lam.1.gz: příkaz nenalezen
mpirun_lam.1.gz: команда не найдена
mpirun_lam.1.gz: командата не е открита
mpirun_lam.1.gz: 命令找不到
mpirun_lam.1.gz: コマンドが見つかりません