"mount: / is busy" when trying to mount as read-only so that I can run zerofree

view full story

http://unix.stackexchange.com – I am trying to run zerofree on Ubuntu 11.04 so that I can compact the VirtualBox vdi image using: VBoxManage modifyhd Ubuntu.vdi --compact In order to run zerofree the disk image has be mounted as read-only. I'm following these instructions which says to use this to remount as read-only from the recovery mode (Drop to root shell prompt): mount -n -o remount,ro -t ext2 /dev/sda1 / But when I do this I get the error: mount: / is busy Any ideas on how to do this? Follow up: Following Jari's answer and this post by running these commands resolves the issue. service rsyslog stop service (HowTos)