大家好，我遇到了一个NFS挂载的奇怪问题，想请各位帮忙分析下：

我使用的是Ubuntu 20.04系统，防火墙采用IPTables。我已经在防火墙中明确配置了NFS相关端口的入站和出站允许规则，同时也允许了相关/已建立的会话通行。

为了固定NFS端口，我在所有服务器的/etc/sysctl.conf中添加了以下配置：

fs.nfs.nlm_udpport=38073
fs.nfs.nlm_tcpport=38747

另外在nfs-kernel-server里将端口设置为33333。

防火墙中已经开放了以下端口的双向（入站+出站）规则：

• 111
• 1110
• 2949
• 33333
• 4045
• 38073
• 38747

但当我通过命令行执行挂载操作时，会出现如下报错：

mount.nfs: timeout set for Fri Sep 15 17:25:35 2023
mount.nfs: trying text-based options 'vers=4.2,addr=192.168.30.150,clientaddr=192.168.10.125'
mount.nfs: mount(2): No such file or directory
mount.nfs: trying text-based options 'addr=192.168.30.150'
mount.nfs: prog 100003, trying vers=3, prot=6
mount.nfs: trying 192.168.30.150 prog 100003 vers 3 prot TCP port 2049
mount.nfs: prog 100005, trying vers=3, prot=17
mount.nfs: portmap query failed: RPC: Unable to send - Operation not permitted
mount.nfs: Operation not permitted

奇怪的是，如果把挂载配置写入fstab中，系统重启时却能正常完成挂载。

补充编辑 #

我还发现一个细节：如果清空IPTables的所有规则，命令行挂载虽然仍会出现mount(2): No such file or directory的提示，但最终能成功挂载，日志如下：

mount.nfs: timeout set for Sat Sep 16 12:47:04 2023
mount.nfs: trying text-based options 'vers=4.2,addr=192.168.30.150,clientaddr=192.168.10.125'
mount.nfs: mount(2): No such file or directory
mount.nfs: trying text-based options 'addr=192.168.30.150'
mount.nfs: prog 100003, trying vers=3, prot=6
mount.nfs: trying 192.168.30.150 prog 100003 vers 3 prot TCP port 2049
mount.nfs: prog 100005, trying vers=3, prot=17
mount.nfs: portmap query retrying: RPC: Timed out
mount.nfs: prog 100005, trying vers=3, prot=6
mount.nfs: trying 192.168.30.150 prog 100005 vers 3 prot TCP port 33333

有没有大佬能帮我排查下问题所在？

备注：内容来源于stack exchange，提问作者Jwaltrip4