fsrefs: 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/fsrefs - from package: python-zodb
/usr/lib/zope2.13/bin/fsrefs - from package: zope2.13

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

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