Mount NFS - "operation not permitted" in Proxmox container

I'm trying to mount a simple NFS share, but it keeps saying "operation not permitted". The NFS server has the following share. /mnt/share_dir 192.168.7.101(ro,fsid=0,all_squash,async,no_subtree_check) 192.168.7.11(ro,fsid=0,all_squash,async,no_subtree_check) The share seems to be active for both clients. # exportfs -s /mnt/share_dir 192.168.7.101(ro,async,wdelay,root_squash,all_squash,no_subtree_check,fsid=0,sec=sys,ro,secure,root_squash,all_squash) /mnt/share_dir 192.168.7.11(ro,async,wdelay,root_squash,all_squash,no_subtree_check,fsid=0,sec=sys,ro,secure,root_squash,all_squash) The client 192.168.7.101 can see the share. $ sudo showmount -e 192.168.7.10 Export list for 192.168.7.10: /mnt/share_dir 192.168.7.101 192.168.7.101 's mount destination: # ls -lah /mnt/share_dir/ total 8.0K drwxr-xr-x 2 me me 4.0K Aug 28 19:21 . drwxr-xr-x 3 root root 4.0K Aug 28 19:21 .. When I try to mount the share, the client says "operation not permitted" with either nfs or nfs4 type. $ sudo mount -vvv -t nfs 192.168.7.10:/mnt/share_dir /mnt/share_dir mount.nfs: timeout set for Sun Aug 28 21:56:03 2022 mount.nfs: trying text-based options 'vers=4.2,addr=192.168.7.10,clientaddr=192.168.7.101' mount.nfs: mount(2): Operation not permitted mount.nfs: trying text-based options 'addr=192.168.7.10' mount.nfs: prog 100003, trying vers=3, prot=6 mount.nfs: trying 192.168.7.10 prog 100003 vers 3 prot TCP port 2049 mount.nfs: prog 100005, trying vers=3, prot=17 mount.nfs: trying 192.168.7.10 prog 100005 vers 3 prot UDP port 46169 mount.nfs: mount(2): Operation not permitted mount.nfs: Operation not permitted I've set fsid=0 and insecure to the export options, but it didn't work. RPCInfo from the client's side: # rpcinfo -p 192.168.7.10 program vers proto port service 100000 4 tcp 111 portmapper 100000 3 tcp 111 portmapper 100000 2 tcp 111 portmapper 100000 4 udp 111 portmapper 100000 3 udp 111 portmapper 100000 2 udp 111 portmapper 100005 1 udp 59675 mountd 100005 1 tcp 37269 mountd 100005 2 udp 41354 mountd 100005 2 tcp 38377 mountd 100005 3 udp 46169 mountd 100005 3 tcp 39211 mountd 100003 3 tcp 2049 nfs 100003 4 tcp 2049 nfs 100227 3 tcp 2049 100003 3 udp 2049 nfs 100227 3 udp 2049 100021 1 udp 46745 nlockmgr 100021 3 udp 46745 nlockmgr 100021 4 udp 46745 nlockmgr 100021 1 tcp 42571 nlockmgr 100021 3 tcp 42571 nlockmgr 100021 4 tcp 42571 nlockmgr Using another client, *192.168.7.11*, I was able to mount that share with no issues. I can not see any issue or misconfiguration, and could not find a fix anywhere. There's no firewall in the way and both server and client are using Debian 11. Any idea of what's going on?