Hello Cephers,

I am trying to understand how uid and gid are handled on the shared cephfs 
mount.  I am using 14.2.2 and cephfs kernel based client.
I have 2 client vms with following uid gid

vm1 user dev (uid=500) group dev (gid=500)
vm2 user dev (uid=500) group dev (gid=500)


vm1 user tomcat (uid=996) group tomcat (gid=995)
vm2 user tomcat (uid=990) group tomcat (gid=990)


on both machines user tomcat is added to a group dev.


Directory /webcluster/data is a kernel cephfs mount and has permissions visible 
on both clients as

rwxrwxr-x dev dev  /webcluster/data

also

rwxr-xr-x root root /webcluster

So it is my understanding that on both vms I should be able to successfully run

touch /webcluster/data/foo as user tomcat.

However,  on vm2 I get permission denied when I attempt to write a file in 
/webcluster/data.
When I change uid and gid of tomcat on vm2 to match those on vm1, then I 
successfully can write into  /webcluster/data.

As on both machines user tomcat is a member of group dev and group dev is 
allowed to write in the directory, why do the uids of the group members need to 
match across network?


I tried research it on my own and failed to find a good explanation.


Thank you for your help,

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