transmission-qt: 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/transmission-qt - from package: transmission-qt

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

On Debian possible default full paths are:

/usr/bin/transmission-qt - from package: transmission-qt

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

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