How to ping from the QEMU guest to an external URL?

Question

The network is working fine, since I can do from inside QEMU:

wget example.com

But if I do:

ping example.com

it just shows the initial header and hangs:

PING example.com (93.184.216.34): 56 data bytes

I know ping requires some extra permissions to run as mentioned at: https://stackoverflow.com/questions/37512291/how-is-ping-for-non-root-user-implemented-on-linux-distros

I tried the procedure at https://wiki.qemu.org/Documentation/Networking#Enabling_ping_in_the_guest.2C_on_Linux_hosts with on host:

sudo groupadd unpriv_ping
sudo usermod --append --groups unpriv_ping "$(id -nu)"
GROUP_ID="$(getent group unpriv_ping | cut -f 3 -d :)"
printf "net.ipv4.ping_group_range = ${GROUP_ID} ${GROUP_ID}\n" | sudo tee -a /etc/sysctl.conf
sudo sysctl -p

then I logged out and in again, but it did not help.

Neither did:

setcap cap_net_raw+eip qemu-system-x86_64

My full QEMU command line is:

x86_64-softmmu/qemu-system-x86_64 \
  -device \
  rtl8139,netdev=net0 \
  -gdb \   
  tcp::45457 \                                                                                                               
  -kernel \   
  /home/ciro/bak/git/linux-kernel-module-cheat/out/linux/default/x86_64/arch/x86/boot/bzImage \
  -m \                                                                                                                                           
  256M \
  -monitor \                                                        
  telnet::45454,server,nowait \
  -netdev \
  user,hostfwd=tcp::45455-:45455,hostfwd=tcp::45456-:22,id=net0 \         
  -no-reboot \
  -smp \
  1 \
  -trace \        
  enable=pr_manager_run,file=/home/ciro/bak/git/linux-kernel-module-cheat/out/run/qemu/x86_64/0/trace.bin \                                         
  -virtfs \                                                                                                                                            
  local,path=/home/ciro/bak/git/linux-kernel-module-cheat/data/9p,mount_tag=host_data,security_model=mapped,id=host_data \
  -virtfs \                                      
  local,path=/home/ciro/bak/git/linux-kernel-module-cheat/out,mount_tag=host_out,security_model=mapped,id=host_out \
  -virtfs \                                                                      
  local,path=/home/ciro/bak/git/linux-kernel-module-cheat/rootfs_overlay,mount_tag=host_rootfs_overlay,security_model=mapped,id=host_rootfs_overlay \
  -serial \                                                                    
  mon:stdio \                                                                    
  -M \                                                                           
  pc \                                          
  -device \                                              
  edu \                              
  -append \                                                                                                                      
  'root=/dev/vda nopat console_msg_format=syslog nokaslr norandmaps panic=-1 printk.devkmsg=on printk.time=y console=ttyS0' \
  -nographic \                                                                
  -drive \                                                                                      
  file=/home/ciro/bak/git/linux-kernel-module-cheat/out/buildroot/build/default/x86_64/images/rootfs.ext2.qcow2,format=qcow2,if=virtio,snapshot \
; 

Tested on Ubuntu 18.04 host with the following images:

• this Buildroot setup
• debootstrap: Creating bootable Debian image with debootstrap

Answer 1

After doing the host computer setup, reboot the computer instead of just logging out and in and it ping then works.