user namespaces: user mapping

["U.Mutlu" <for-gmane@mutluit.com>]

Mike Frysinger wrote on 11/16/2015 05:19 AM:
> On 16 Nov 2015 03:26, U.Mutlu wrote:
>
>> The other solution via user namespace is IMHO overkill and in my case
>> impractical and irritating because user gets a root-prompt (#)
>> eventhough it is only inside the user namespace.
>
> so remap it to your own user instead of to root

Sorry, I forgot the dangers of mounting into existing mount namespace.
Yes, user namespace seems to be the way to go, so I tried the sample from
man user_namespaces:

$ ./userns_child_exec -v -p -m -U -z bash
./userns_child_exec: PID of child created by clone() is 2950
ERROR: write /proc/2950/gid_map: Operation not permitted
About to exec bash

Am I on the right track with the above method for user remapping?

It's maybe that under Debian another sysctl-setting is needed
for this to work, I'll need to do some research on the net.
If someone here knows the solution let me know pls.