pixeltool: 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/pixeltool - from package: qt5-qttools-devel
/usr/lib/qt5/bin/pixeltool - from package: qt5-qttools-devel
/usr/bin/pixeltool - from package: qt-devel
/usr/lib64/qt4/bin/pixeltool - from package: qt-devel
/usr/lib/qt4/bin/pixeltool - from package: qt-devel

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

On Debian possible default full paths are:

/usr/bin/pixeltool - from package: qtchooser
/usr/lib/x86_64-linux-gnu/qt4/bin/pixeltool - from package: qt4-dev-tools
/usr/lib/x86_64-linux-gnu/qt5/bin/pixeltool - from package: qttools5-dev-tools

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

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