pi3topbm: 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/pi3topbm - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pi3topbm - from package: netpbm

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

Error in other languages:
pi3topbm: bevel nie gevind nie
pi3topbm: comandă negăsită
pi3topbm: comando não encontrado
pi3topbm: commande introuvable
pi3topbm: command not found
pi3topbm: käsku ei ole
pi3topbm: không tìm thấy lệnh
pi3topbm: komanda nerasta
pi3topbm: Kommando nicht gefunden.
pi3topbm: kommandot finns inte
pi3topbm: komut yok
pi3topbm: nie znaleziono polecenia
pi3topbm: níor aimsíodh an t-ordú
pi3topbm: no se encontró la orden
pi3topbm: no s'ha trobat l'ordre
pi3topbm: opdracht niet gevonden
pi3topbm: parancs nem található
pi3topbm: perintah tidak ditemukan
pi3topbm: príkaz nenájdený
pi3topbm: příkaz nenalezen
pi3topbm: команда не найдена
pi3topbm: командата не е открита
pi3topbm: 命令找不到
pi3topbm: コマンドが見つかりません