mounted ISO; What determines available room?

Robert Heller heller at deepsoft.com
Tue Dec 31 01:04:02 UTC 2019


At Mon, 30 Dec 2019 19:14:31 -0500 "Ubuntu user technical support,  not for general discussions" <ubuntu-users at lists.ubuntu.com> wrote:

> 
> Once an ISO file is mounted for use like in an install ISO, what
> factors determine how much room is available?
> 
> Example of what I mean with the ubuntu focal fossa  20.4 iso:
> 
> inside mounted ISO:
> 
> df -h
> 
> Filesystem      Size  Used Avail Use% Mounted on
> udev            2.4G     0  2.4G   0% /dev
> tmpfs           494M  1.1M  493M   1% /run
> /dev/sr0        1.6G  1.6G     0 100% /cdrom
> /dev/loop0      1.5G  1.5G     0 100% /rofs
> /cow            2.5G  104M  2.4G   5% /
> tmpfs           2.5G   16M  2.4G   1% /dev/shm
> tmpfs           5.0M  4.0K  5.0M   1% /run/lock
> tmpfs           2.5G     0  2.5G   0% /sys/fs/cgroup
> tmpfs           2.5G   84K  2.5G   1% /tmp
> tmpfs           494M  8.0K  494M   1% /run/user/999
> tmpfs           494M     0  494M   0% /run/user/0
> 
> Notice root shows 5% used and a Size of 2.5G
> 
> How would someone making this iso arrange things so that the size was
> 7GB for `/'  Or any other size for that matter.

I expect that the init script run as part of the boot process "creates" the 
root file system.  The tmpfs "filesystems" are a type of ramdisk (I expect 
that they are sparse ramdisks, where the "empty" blocks are allocated from 
virtual memory as they are allocated).

The root file system is probably something a squashfs or created from a 
squashfs.  You will need to look at the init ramdisk file, located somewhere 
under /cdrom for the exact code...

> 
> 
> 

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