unionfs-fuse: 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/unionfs-fuse - from package: unionfs-fuse

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

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