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From: Laszlo Ersek <lersek@redhat.com>
Message-ID: <57208ECE.4040400@redhat.com>
Date: Wed, 27 Apr 2016 12:05:02 +0200
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Subject: Re: [Qemu-devel] Is anyone able to load a web page from a guest
 operating system?
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To: Thomas Huth <thuth@redhat.com>, Programmingkid <programmingkidx@gmail.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>, qemu-devel qemu-devel <qemu-devel@nongnu.org>

On 04/26/16 22:12, Thomas Huth wrote:
> On 26.04.2016 21:25, Programmingkid wrote:
>> On Apr 26, 2016, at 3:00 PM, Dr. David Alan Gilbert wrote:

>>> Does ping work?
>> I can ping the virtual router at 10.0.2.2. Any other ip address fails. 
> 
> That's normal for user-mode / slirp networking. You can't ping external
> hosts with this mode.

Side note: yes, you can.

I do it whenever I want to check network connectivity from within ad-hoc
OVMF guests, using the PING command of the UEFI shell. ("Ad-hoc guest"
implies user-mode / slirp.)

It can be enabled with the following steps:

(1) Determine the main group ID (or one supplementary group ID) of the
user that will run QEMU with slirp.

(2) In /etc/sysctl.conf (or whatever is appropriate for your host
distro), make sure that the whitespace separated inclusive group ID
range in the "net.ipv4.ping_group_range" sysctl includes the above group ID.

For example,

- you could add a new group called "unpriv_ping":

  groupadd unpriv_ping

- set this group for a number of users as another supplementary group:

  for U in user1 user2 ... usern; do
    usermod --append --groups unpriv_ping $U
  done

  (note, they will have to re-login),

- then set both sides of the inclusive range in the above sysctl to the
  numeric ID of the new group:

  (
    GROUP_ID=$(getent group unpriv_ping | cut -f 3 -d :)
    printf 'net.ipv4.ping_group_range = %u %u\n' $GROUP_ID $GROUP_ID \
      >> /etc/sysctl.conf
  )
  sysctl -p

Thanks
Laszlo