pfssize: 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/pfssize - from package: pfstools

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

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