tm_mupad: 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/libexec/TeXmacs/bin/tm_mupad - from package: TeXmacs

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

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