icontopbm: 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/icontopbm - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/icontopbm - from package: netpbm

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

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