c3270: 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/c3270 - from package: x3270-text

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

Error in other languages:
c3270: bevel nie gevind nie
c3270: comandă negăsită
c3270: comando não encontrado
c3270: commande introuvable
c3270: command not found
c3270: käsku ei ole
c3270: không tìm thấy lệnh
c3270: komanda nerasta
c3270: Kommando nicht gefunden.
c3270: kommandot finns inte
c3270: komut yok
c3270: nie znaleziono polecenia
c3270: níor aimsíodh an t-ordú
c3270: no se encontró la orden
c3270: no s'ha trobat l'ordre
c3270: opdracht niet gevonden
c3270: parancs nem található
c3270: perintah tidak ditemukan
c3270: príkaz nenájdený
c3270: příkaz nenalezen
c3270: команда не найдена
c3270: командата не е открита
c3270: 命令找不到
c3270: コマンドが見つかりません