pyrsa-decrypt-bigfile: 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 CentOS possible default full paths are:

/usr/bin/pyrsa-decrypt-bigfile - from package: python2-rsa

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/pyrsa-decrypt-bigfile - from package: python-rsa

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

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