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I want to remount /dev/sda2 [mounted on /var/www] as readonly

# mount -o remount,ro /var/www
mount: /var/www is busy

There are no open files on that filesystem

# fuser -v -m /var/www
                     USER        PID ACCESS COMMAND
/var/www:            root     kernel mount /var/www
# lsof -V /var/www
lsof: no file system use located: /var/www

Nothing nfs-like is running. No swapfiles under /var/www. No loop devices in use.

Why is /var/www still busy?

Nothing mounted under /var/www:

# mount
/dev/root on / type ext4 (rw,noatime,nodelalloc)
tmpfs on /run type tmpfs (rw,nosuid,noexec,relatime,size=155344k,mode=755)
tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,relatime,size=310684k)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev type tmpfs (rw,relatime,size=10240k,mode=755)
tmpfs on /run/shm type tmpfs (rw,nosuid,nodev,relatime,size=310684k)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620)
/dev/sda2 on /var/www type ext4 (rw,noatime,nodelalloc)
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Anything mounted below /var/www? – Paul Jun 4 '12 at 12:30
Nothing mounted below /var/www. I added the mounts in the question – user49740 Jun 4 '12 at 17:08
up vote 3 down vote accepted

By killing various processes I found out that gamin was keeping the mount busy. I still wonder why this didn't show up in either lsof nor fuser

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