On 2015-05-06 13:05, Chris Murphy wrote:
> Ok so now that my mea culpa is out of the way, I'm actually wondering
> why non-root users can't do certain btrfs tasks when they're read-only
> commands.
>
> [chris@f22m ~]$ btrfs fi show
> ERROR: could not open /dev/sda7   ##this is new it wasn't doing this last night
> btrfs-progs v4.0
> [chris@f22m ~]$ btrfs fi df /
> Data, single: total=4.00GiB, used=3.57GiB
> System, single: total=4.00MiB, used=16.00KiB
> Metadata, single: total=1.01GiB, used=198.30MiB
> GlobalReserve, single: total=80.00MiB, used=0.00B
> [chris@f22m ~]$ btrfs fi usage /
> WARNING: can't read detailed chunk info, RAID5/6 numbers will be
> incorrect, run as root
> WARNING: can't get filesystem info from ioctl(FS_INFO), run as root
> ERROR: couldn't get space info on '/' - Operation not permitted
>
>
> I think usage is more useful than df for users, and contains largely
> the same information as df + show, so I think all three should be
> non-root user usable.
>
That may be tricky to do, I think show and usage both access the 
underlying block device directly (or try to in any case), which would 
explain why they don't work as non-root; most modern linux distributions 
have permissions on (non-hot-plugged) block devices set to 660 and owned 
by root:disk.