jam: 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/jam - from package: jam

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

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