mothur-mpi: 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/mothur-mpi - from package: mothur-mpi

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

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