portsentry: 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/sbin/portsentry - from package: portsentry

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

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