umount.davfs: 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 CentOS possible default full paths are:

/sbin/umount.davfs - from package: davfs2
/usr/sbin/umount.davfs - from package: davfs2

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/sbin/umount.davfs - from package: davfs2
/usr/sbin/umount.davfs - from package: davfs2

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

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