six: 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/lib64/gambit-c/bin/six - from package: gambit-c

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

On Debian possible default full paths are:

/usr/bin/six - from package: gambc

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

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