gtk-update-icon-cache: 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/gtk-update-icon-cache - from package: gtk2

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

On Debian possible default full paths are:

/usr/bin/gtk-update-icon-cache - from package: libgtk2.0-bin

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

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