[lustre-discuss] Question about permissions on directory with sticky bit set with 2.16.1 client, 2.12.6 server Lewis

[Lewis Hyatt]

Hello-

I have a lustre server running 2.12.6. I am planning to upgrade the
clients (not the server) from Ubuntu 18 to Ubuntu 24, and I am testing
this configuration using lustre 2.16.1 on the client side. So far, it
builds and performs just fine like this, but I have come across one
obscure issue. If a file resides in a world-writable directory with
the sticky bit set, then I am not able to append to files in that
directory as the root user. As an example:

$ uname -r
6.8.0-51-generic
$ lfs --version
lfs 2.16.1
$ mkdir tmp
$ chmod 1777 tmp
$ cd tmp
$ touch f
$ chmod 644 f
$ sudo chown nobody f  #any user other than the current user goes here
$ sudo su
# echo >> f
bash: f: Permission denied

strace sees:

openat(AT_FDCWD, "f", O_WRONLY|O_CREAT|O_APPEND, 0666) = -1 EACCES
(Permission denied)

The above sequence works as expected for non-lustre filesystems on the
same client, and it works for lustre with the same lustre server on
the Ubuntu 18 clients running lustre client 2.12.9_11_g60c2827.

I am wondering if this change is expected or if there's something I
can configure to preserve the previous behavior... thanks very much in
advance for any help!

-Lewis