NFS服务器无法开机自启但可手动启动问题求助

各位大佬好，我碰到一个头疼的问题，想请大家帮忙分析下：

我的NFS服务器开机时没法正常导出目录，但等系统启动完成后，我通过SSH连进去手动启动服务就能正常运行。为了排除权限方面的问题，我已经把相关目录的所有者、组和权限都设置得非常宽松了，打算等问题解决后再把权限收紧。另外说明下，这个服务器只在我的局域网内访问，不会对外暴露。

开机启动失败时的systemctl status nfs-kernel-server.service输出： #

● nfs-server.service - NFS server and services
Loaded: loaded (/lib/systemd/system/nfs-server.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Mon 2023-02-20 10:22:36 GMT; 27min ago
Process: 303 ExecStartPre=/usr/sbin/exportfs -r (code=exited, status=1/FAILURE)

Feb 20 10:22:36 file-server systemd[1]: Starting NFS server and services...
Feb 20 10:22:36 file-server exportfs[303]: exportfs: Failed to stat /shared/Documents: No such file or directory
Feb 20 10:22:36 file-server exportfs[303]: exportfs: Failed to stat /shared/Downloads: No such file or directory
Feb 20 10:22:36 file-server exportfs[303]: exportfs: Failed to stat /shared/Video: No such file or directory
Feb 20 10:22:36 file-server systemd[1]: nfs-server.service: Control process exited, code=exited status=1
Feb 20 10:22:36 file-server systemd[1]: Failed to start NFS server and services.
Feb 20 10:22:36 file-server systemd[1]: nfs-server.service: Unit entered failed state.
Feb 20 10:22:36 file-server systemd[1]: nfs-server.service: Failed with result 'exit-code'.

手动执行systemctl start nfs-kernel-server.service后的状态输出： #

● nfs-server.service - NFS server and services
Loaded: loaded (/lib/systemd/system/nfs-server.service; enabled; vendor preset: enabled)
Active: active (exited) since Mon 2023-02-20 10:51:34 GMT; 1min 4s ago
Process: 735 ExecStart=/usr/sbin/rpc.nfsd $RPCNFSDARGS (code=exited, status=0/SUCCESS)
Process: 732 ExecStartPre=/usr/sbin/exportfs -r (code=exited, status=0/SUCCESS)
Main PID: 735 (code=exited, status=0/SUCCESS)

Feb 20 10:51:33 file-server systemd[1]: Starting NFS server and services...
Feb 20 10:51:34 file-server systemd[1]: Started NFS server and services.

服务器基本信息： #

• IP地址：192.168.1.200（DHCP分配，路由器已设置IP保留）
• 磁盘挂载：
  • sda的分区为ext4，开机挂载为/和swap
  • sdb的分区为ext4，开机挂载为/shared

/etc/fstab内容： #

#sda1
UUID=4c5189b4-6ed8-416a-9b45-d7a8cb7d1f76 /               ext4    errors=remount-ro 0       1
#sda2
UUID=85704cdf-46ff-4a71-83a0-deebf37f9f82 none            swap    sw              0       0
#sdb1
UUID=98c91985-fe1b-43d0-8c62-a6edb9184a35 /shared ext4 nofail,sync,auto,noexec,nosuid,rw,nouser 1 2

/etc/exports内容： #

/shared/Video 192.168.1.0/24(rw,sync,no_subtree_check)
/shared/Downloads 192.168.1.0/24(rw,sync,no_subtree_check)
/shared/Documents 192.168.1.0/24(rw,sync,no_subtree_check)

相关目录权限信息： #

• 挂载点/shared的权限：

drwxrwxrwx 7 nobody nogroup 4096 Aug 18  2022 /shared/

• /shared下各子目录的权限（lost+found未共享）：

drwxrwxrwx  27 nobody nogroup 12288 Jan 26 19:45 /shared/Documents/
drwxrwxrwx  25 nobody nogroup  4096 Aug 18  2022 /shared/Downloads/
drwx------   2 root   root    16384 Aug 18  2022 /shared/lost+found/
drwxrwxrwx 162 nobody nogroup 12288 Feb  4 15:03 /shared/Video/

（注：共享目录的权限是递归设置的）

如果需要其他信息，我随时可以提供，麻烦大家帮忙看看问题出在哪了！

备注：内容来源于stack exchange，提问作者David