An error occurred while mounting the nfs file system.

An error occurred while mounting the nfs file system-general Linux technology-Linux technology and application information. For more information, see the following. An error occurred while mounting the nfs file system:
1. Disable the firewall and set the host's IP address to 192.168.1.1.

2. Enable the nfs and portmap services on the host machine (the service runs normally after it is enabled)

3. Edit the/etc/exports file on the host and add the following line to the file:
/Opt/root_nfs * (rw, sync, no_root_squash)

4. Restart the nfs service (normal operation)

5. After the serial port is connected, open the minicom window on the host machine and start the target machine (Development Board)

6. After the target machine starts, enter the ifconfig command in The minicom window and the IP address of the target machine is 192.168.1.6.

7. Input in minicom: ping 192.168.1.1 to ping the host machine

8. Enter "ping 192.168.1.6" on the host machine to ping the target machine, indicating that the network is correct.

9. Set the IP address of another PC (non-host) to 192.168.1.10, and ping 192.168.1.1.

10. Enable the portmap service on 192.168.1.10 PC and disable the nfs service.

11. Mounting nfs on 192.168.1.10 PC is normal:
Mount-t nfs 192.168.1.1:/opt/root_nfs/mnt/nfs

12. Input mount-t nfs 192.168.1.1:/opt/root_nfs/mnt/nfs in The minicom of the host machine. The following error occurs:
Portmap: server localhost not responding, time out
RPC: failed to contact portmap (errno-5)
Portmap: server localhost not responding, time out
RPC: failed to contact portmap (errno-5)
Lockd_up: makesock failed, error =-5
Portmap: server localhost not responding, time out
RPC: failed to contact portmap (errno-5)

On the 192.168.1.10 PC, if the portmap service is disabled and nfs is mounted, an error such as "input/output error" may occur,
Is it because the portmap service on the target machine is not enabled, but how can this service be enabled? The portmap service is not found in the/etc/init. d directory.
If it is not the reason for the portmap service, why?
The target machine is the TQ2440 Development Board of youlong, and the kernel is Linux2.6 kernel for S3C2440.