Make one directory writeable

Make one directory writeable

[Bhupendra Singh]

[-- Attachment #1: Type: text/plain, Size: 277 bytes --]

Hello 

I have built core-image-minimal  with read only rootfs  then now  I want to
make one directory (like /mnt) writable. 

Is it possible to make one directory writeable in read only rootfs if yes
,please tell me how can I do same.   

 

Bhupendra Singh

 


[-- Attachment #2: Type: text/html, Size: 2901 bytes --]

Re: Make one directory writeable

[Ulf Samuelsson]

[-- Attachment #1: Type: text/plain, Size: 934 bytes --]

You can use overlayfs for this. You mount the overlayfs on top of your rootfs and then it appear like you have a writeable file system.
In reality all the new  stuff is written to another (writeable) file system.
If you dismount the overlayfs, the rootfs reverts back to its original state.
If you again  mount the overlayfs, you get your modifications back.

Best Regards,
Ulf Samuelsson
+46 722 427 437

> 13 feb. 2019 kl. 08:21 skrev Bhupendra Singh <bhupendra.singh@ppsinternational.in>:
> 
> Hello
> I have built core-image-minimal  with read only rootfs  then now  I want to make one directory (like /mnt) writable.
> Is it possible to make one directory writeable in read only rootfs if yes ,please tell me how can I do same.   
>  
> Bhupendra Singh
>  
> -- 
> _______________________________________________
> yocto mailing list
> yocto@yoctoproject.org
> https://lists.yoctoproject.org/listinfo/yocto

[-- Attachment #2: Type: text/html, Size: 3868 bytes --]

Re: Make one directory writeable

[Josef Holzmayr]

Hi Bhupendra,

On Wed, Feb 13, 2019 at 12:51:17PM +0530, Bhupendra Singh wrote:
> Hello 
> 
> I have built core-image-minimal  with read only rootfs  then now  I want to
> make one directory (like /mnt) writable. 
> 
> Is it possible to make one directory writeable in read only rootfs if yes
> ,please tell me how can I do same.   

This is not exactly yocto specific, general linux concepts apply. You
can use a secondary, tertiary, ... partition or starage device and then
mount that as read-write. But it always has to be a seperate filesystem.
There is no way to make only one path of a given filesystem RW, it
always means that the whole filesystem is writeable.

Greetz
-- 
———————————————
Josef Holzmayr
Software Developer Embedded Systems

Tel: +49 8444 9204-48
Fax: +49 8444 9204-50

R-S-I Elektrotechnik GmbH & Co. KG
Woelkestrasse 11
D-85301 Schweitenkirchen
www.rsi-elektrotechnik.de
———————————————
Amtsgericht Ingolstadt – GmbH: HRB 191328 – KG: HRA 170393
Geschäftsführer: Dr.-Ing. Michael Sorg, Dipl.-Ing. Franz Sorg
Ust-IdNr: DE 128592548 

_____________________________________________________________
Amtsgericht Ingolstadt - GmbH: HRB 191328 - KG: HRA 170363
Geschäftsführer: Dr.-Ing. Michael Sorg, Dipl.-Ing. Franz Sorg
USt-IdNr.: DE 128592548

Re: Make one directory writeable

[Mike Looijmans]

As for the particular case of /mnt, on most images, /mnt is a symlink to 
/media, and /media is (on) a filesystem in RAM, so it's already writeable.

If the write does not need to persist across reboots, use a tmpfs mount.

If your real problem is that you cannot create anything in /mnt (or /media for 
modern users), the issue is that someone broke something in your image, 
because that should work out of the box.


On 13-02-19 09:27, Josef Holzmayr wrote:
> Hi Bhupendra,
> 
> On Wed, Feb 13, 2019 at 12:51:17PM +0530, Bhupendra Singh wrote:
>> Hello
>>
>> I have built core-image-minimal  with read only rootfs  then now  I want to
>> make one directory (like /mnt) writable.
>>
>> Is it possible to make one directory writeable in read only rootfs if yes
>> ,please tell me how can I do same.
> 
> This is not exactly yocto specific, general linux concepts apply. You
> can use a secondary, tertiary, ... partition or starage device and then
> mount that as read-write. But it always has to be a seperate filesystem.
> There is no way to make only one path of a given filesystem RW, it
> always means that the whole filesystem is writeable.
> 
> Greetz
>