qmlviewer: 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/lib64/qt5/bin/qmlviewer - from package: qt5-qtquick1-devel
/usr/lib/qt5/bin/qmlviewer - from package: qt5-qtquick1-devel

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

On Debian possible default full paths are:

/usr/lib/x86_64-linux-gnu/qt4/bin/qmlviewer - from package: qt4-qmlviewer
/usr/bin/qmlviewer - from package: qtchooser
/usr/lib/x86_64-linux-gnu/qt5/bin/qmlviewer - from package: qtquick1-5-dev-tools

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

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