How to debug linux networking: Address already in use
If your host is an NFS client, it may be using source port 874 for an NFS mount. I suspect that because the connection does not originate from userspace it may not be visible to the tools you've used so far.
Consider one of the following:
- Adjust the
sysctlssunrpc.min_resvportandsunrpc.max_resvport(default 665 and 1023) to change the range of source ports that the NFS client uses - Use a listening port outside of this range
- Use the
noresvportoption on the NFS mount to use the non-privileged range (may have security implications)