[Unionfs] Problem with unionfs

[Jesse I Pollard]

Stephan Schöffel wrote:
> 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.
>
>
Does the directory (the tmp_snap) have rwxrwxrwt permissions?
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