5250keys: 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/5250keys - from package: tn5250

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

Error in other languages:
5250keys: bevel nie gevind nie
5250keys: comandă negăsită
5250keys: comando não encontrado
5250keys: commande introuvable
5250keys: command not found
5250keys: käsku ei ole
5250keys: không tìm thấy lệnh
5250keys: komanda nerasta
5250keys: Kommando nicht gefunden.
5250keys: kommandot finns inte
5250keys: komut yok
5250keys: nie znaleziono polecenia
5250keys: níor aimsíodh an t-ordú
5250keys: no se encontró la orden
5250keys: no s'ha trobat l'ordre
5250keys: opdracht niet gevonden
5250keys: parancs nem található
5250keys: perintah tidak ditemukan
5250keys: príkaz nenájdený
5250keys: příkaz nenalezen
5250keys: команда не найдена
5250keys: командата не е открита
5250keys: 命令找不到
5250keys: コマンドが見つかりません