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. Valeri ++++++++++++++++++++++++++++++++++++++++ Valeri Galtsev Sr System Administrator Department of Astronomy and Astrophysics Kavli Institute for Cosmological Physics University of Chicago Phone: 773-702-4247 ++++++++++++++++++++++++++++++++++++++++