[CentOS] What is /etc/subuid ?

Wed Oct 9 19:56:50 UTC 2019
Mike Burger <mburger at bubbanfriends.org>

On 2019-10-09 15:47, Valeri Galtsev wrote:
> Dear Experts,
> Could someone enlighten me about the following file:
> /etc/subuid
> ? This file appears to be owned by "setup" package. This is CentOS 7
> system, and until now these files if existed were never changed. Today
> I have added user quite routine way, by doing
> /usr/sbin/groupadd -g 4500 [username]
> /usr/sbin/useradd -g [username] -u 4500 -c "User Name, email at domain" 
> [username]
> And the file /etc/subuid changed and user was added into it:
> [username]:100000:65536
> Nothing like that was happening before. This is first time I create
> account after update done on Oct 3, 2019. I checked several CentOS 7
> machines, basically doing this:
>  # grep subuid /usr/sbin/useradd
> Binary file /usr/sbin/useradd matches
> And CentOS 7 machines indeed may have that file name in the useradd
> binary. None of CentOS 6 machines has that.
> I tried to do FreeBSD-ism:
> man /etc/subuid
> came empty, and realized that I'm doing FreeBSD-ism.
> I tried to do search on the web (did not "google", I use duckduckgo...
> so I "did search"), and came pretty much empty.
> Is it just me, or indeed something in CentOS 7 indeed changed? And what 
> is it?
> Another question on the same note: how do we find out what the file is
> about and is used for in Linux, apart from searching on the web. (When
> there are surprises like the one I had today, one does like to know
> what this particular file is used for).
> Thanks in advance for your answers.

A quick google search:


yielded this as the first link:


Mike Burger

"It's always suicide-mission this, save-the-planet that. No one ever 
just stops by to say 'hi' anymore." --Colonel Jack O'Neill, SG1