[Unionfs] Problem with unionfs

[Stephan Schöffel]

Jesse I Pollard schrieb:
> Stephan Schöffel wrote:
>> hi there,
>>
>> i'm still new to unionfs. i followed the tutorial on this website 
>> http://flaviostechnotalk.com/wordpress/index.php/2005/06/28/filesystem-snapshots-with-unionfs/ 
>> which was linked at the unionfs website.
>>
>> the example did work but it does not fit my problem properly. i tries 
>> different things but could not get it to work the way i want.
>>
>> here is what i want:
>>
>> i want (via script and using unionfs) to bring different directories 
>> to their original state if the machine is rebooted. eg i want to 
>> delete files users write to /tmp
>> i used the following approach:
>>
>> modprobe unionfs
>> mkdir /tmp_union
>> mount -t unionfs -o dirs=/tmp=rw unionfs /tmp_union
>> mkdir /tmp_snap
>>
>> unionctl /tmp_union --add --mode rw /tmp_snap
>> unionctl --mode ro /tmp
>>
>>
>>
>>
>> unfortunately, users can still write to /tmp and the changes are not 
>> logged in /tmp_snap. is there a way to bring /tmp back to its 
>> original state by using unionfs?
> I'm going out on limb, but what you want depends on other things:
>
> 1. do you use a disk based filesystem for /tmp?
> 2. do you need large amount of space for /tmp?
>
> One reason for these questions is that you COULD use a ramfs for /tmp. 
> On every
> reboot, ram is cleared.
>
> Aternative to ramfs or unionfs:
>
> If a resident disk based filesystem is required, then just mkfs that 
> filesystem
> before mounting it. An /etc/rc script with something like:
>
> mkfs /dev/hda6
> mount /dev/hda6 /tmp
>
> Even if you do want to use a unionfs, you will have to mount that 
> union on /tmp
> to prevent users from accessing the underlying filesystem:
>
> 1. mount the scratch filesystem somewhere users cant directly get to 
> it, such as
>       /var/scratch/tmp_snap
>   and make /var/scratch only accessable to root.
>
> 2. The readonly FS underlying scratch must be mounted somewhere users 
> can't get to
>   either:
>       /var/scratch/tmp
>
> 3. Mount the unionfs thus:
>
>    mount -t unionfs -o 
> dirs=/var/scratch/tmp_snap=rw:/var/scratch/tmp=ro none /tmp
>
> 4. and on every boot you still have to erase the tmp_snap.
>
> Personally, I think you need either the ramfs or the non-unionfs version.


i tried as you recommended, unffortunately without success. i was able 
to do the mount but then i would not be able to write files to tmp as a 
user anymore.