icmpush: 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 Debian possible default full paths are:

/usr/bin/icmpush - from package: icmpush

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

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