qtcreator: 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/qtcreator - from package: qt-creator

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

On Debian possible default full paths are:

/usr/bin/qtcreator - from package: qtcreator

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

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