`sudo echo "bla" >> /etc/sysctl.conf` permission denied
Solution 1:
You can't use sudo to affect output redirection; > and >> (and, for completeness, <) are effected with the privilege of the calling user, because redirection is done by the calling shell, not the called subprocess.
Either do
cp /etc/sysctl.conf /tmp/
echo "net.ipv4.ip_forward = 1" >> /tmp/sysctl.conf
sudo cp /tmp/sysctl.conf /etc/
or
sudo /bin/su -c "echo 'net.ipv4.ip_forward = 1' >> /etc/sysctl.conf"
Solution 2:
You might find it simpler to use this command:
echo net.ipv4.ip_forward = 1 | sudo tee -a /etc/sysctl.conf