How to SSH from host to guest using QEMU?

I think the error is not from the -netstatement but from:

-chardev socket,host=localhost,port=7777,server,nowait,id=port1-char

The statement already uses port 7777. For port forwarding, with

-net user,hostfwd=tcp::7777-:8001

It works fine when the virtio serial channel is not set.

If I understand correctly, do you want to establish a virtio serial channel to communicate with the VM from the host using Unix domain sockets?

In this case, you can do the following:

/usr/bin/qemu-system-x86_64 \
-m 1024 \
-name vserialtest \
-hda ubuntu1204 \
-chardev socket,path=/tmp/port1,server,nowait,id=port1-char \
-device virtio-serial \
-device virtserialport,id=port1,chardev=port1-char,name=org.fedoraproject.port.0 \
-net user,hostfwd=tcp::7777-:8001

Example of how to connect to a VM from the host using ssh:

-net user,hostfwd=tcp::10022-:22
-net nic

This host forwarding maps localhost (host) port 10022 to port 22 on the VM. After starting the virtual machine like this, you can access it from localhost as follows:

ssh vmuser@localhost -p10022

The -net nic command initializes a very basic virtual network interface card.