gnome-thumbnail-font: 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/gnome-thumbnail-font - from package: control-center

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

On Debian possible default full paths are:

/usr/bin/gnome-thumbnail-font - from package: gnome-font-viewer

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

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