pyrasite-shell: 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/pyrasite-shell - from package: pyrasite

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

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