pyrsa-encrypt-bigfile-2: 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

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-encrypt-bigfile-2 - from package: python2-rsa

You may install the required package with command yum install {package}
Error in other languages:
pyrsa-encrypt-bigfile-2: bevel nie gevind nie
pyrsa-encrypt-bigfile-2: comandă negăsită
pyrsa-encrypt-bigfile-2: comando não encontrado
pyrsa-encrypt-bigfile-2: commande introuvable
pyrsa-encrypt-bigfile-2: command not found
pyrsa-encrypt-bigfile-2: käsku ei ole
pyrsa-encrypt-bigfile-2: không tìm thấy lệnh
pyrsa-encrypt-bigfile-2: komanda nerasta
pyrsa-encrypt-bigfile-2: Kommando nicht gefunden.
pyrsa-encrypt-bigfile-2: kommandot finns inte
pyrsa-encrypt-bigfile-2: komut yok
pyrsa-encrypt-bigfile-2: nie znaleziono polecenia
pyrsa-encrypt-bigfile-2: níor aimsíodh an t-ordú
pyrsa-encrypt-bigfile-2: no se encontró la orden
pyrsa-encrypt-bigfile-2: no s'ha trobat l'ordre
pyrsa-encrypt-bigfile-2: opdracht niet gevonden
pyrsa-encrypt-bigfile-2: parancs nem található
pyrsa-encrypt-bigfile-2: perintah tidak ditemukan
pyrsa-encrypt-bigfile-2: príkaz nenájdený
pyrsa-encrypt-bigfile-2: příkaz nenalezen
pyrsa-encrypt-bigfile-2: команда не найдена
pyrsa-encrypt-bigfile-2: командата не е открита
pyrsa-encrypt-bigfile-2: 命令找不到
pyrsa-encrypt-bigfile-2: コマンドが見つかりません