petscarch: 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/petscarch - from package: libpetsc3.4.2-dev

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

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