viewres: 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/viewres - from package: xorg-x11-resutils

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

On Debian possible default full paths are:

/usr/bin/viewres - from package: x11-utils

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

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