Re: Easy way to restart network
On Mon, 2011-08-08 at 21:27 +0200, Bob Proulx wrote:
> Tomas Kral wrote:
> > What is the recommended and easy way to restart network subsystem on a
> > desktop without need of rebooting the computer?
>
> This has been a popular topic this week!
>
> > On Lenny I used to, as admin, execute something like this,
> >
> > #!/bin/sh
> > # restart network
> > su -c'\
> > modprobe -r cdc_ether;\
> > modprobe cdc_ether;\
> > cd /etc/init.d;\
> > ./networking stop;\
> > ./networking start;\
> > ./arno-iptables-firewall restart;\
> > cd -\
> > '
> >
> > On Squeeze, it sometimes complains that eth1 device does not exist yet.
> > My idea is to automate the task, and set a watchdog over ISP connection,
> > and call a safe script when it drops to bring it up again.
>
> You didn't show us how your /etc/network/interfaces is set up. It
> would be useful to know if you are using 'auto eth0' / 'auto eth1'
> which I assume you are otherwise the networking stop and start would
> not work, but it is still an assumption I have to make. And without
> that information it makes it hard to guess at your problem with eth1
> not existing yet. Please show us.
>
> On Squeeze you should use the 'service' utility to operate on services
> instead of calling them directly. This is new in Squeeze and
> addresses the problem of environment polution. This doesn't in any
> way change the way '/etc/init.d/service restart' works now but is an
> improvement over it. Since it is now available I recommend using it.
>
> I would reorder the actions to remove the modules after having brought
> down the interface. I expect that is the problem. Probably unloading
> the module brings down the interface and there is a race between which
> happens first. At a guess.
>
> You have backslashes at the end of every line. But you have also
> created a quoted string with semicolons. In this case you don't need
> to have quoted newline continuations. I think it reads better without
> it.
>
> You cd into /etc/init.d and then at the end of the script 'cd -' to
> return and then exit. The current working directory is a property of
> the process and since the process is exiting immediately it is no
> necessary to try to return before exiting. So that 'cd -' can be
> removed.
>
> I would read this reference:
>
> http://www.debian.org/doc/manuals/debian-reference/ch05.en.html
>
> And in particular this section is very useful:
>
> http://www.debian.org/doc/manuals/debian-reference/ch05.en.html#_the_basic_syntax_of_etc_network_interfaces
>
> And then add 'allow-hotplug eth0' so that the interfaces are event
> driven too. Then use ifup and ifdown instead.
>
> #!/bin/sh
> # restart network
> su -c '
> service networking stop;
> modprobe -r cdc_ether;
> sleep 1;
> modprobe cdc_ether;
> service networking start;
> service arno-iptables-firewall restart;
> '
>
> I added a sleep 1 there because I have a system with an Intel chipset
> and it has a vaguely similar problem. I sometimes have to unload and
> reload that module too. I found that it was much more reliable if I
> gave the system a few cycles between unloading and loading. YMMV.
>
> I would be inclined to set up sudo and /etc/sudoers so that this uses
> sudo instead of su. I find it a more convenient solution. It would
> turn this into a normal script instead of a script in the argument
> list and then just sudo that script. Again YMMV.
>
> If you decide to try the ifup/ifdown route it would look like this.
> As an advantage it would not cycle the eth0 network but just eth1.
>
> #!/bin/sh
> # Call script with sudo.
> ifdown eth1
> modprobe -r cdc_ether
> sleep 1
> modprobe cdc_ether
> ifup eth1
> service arno-iptables-firewall restart
>
> As further improvement possibilities, if you look in /etc/network/ you
> will find a series of .d directories such as /etc/network/if-up.d/ and
> in there scripts. You could have the firewall script automatically
> restart whenever the network comes online.
>
> File something like /etc/network/if-up.d/local-firewall-restart:
> #!/bin/sh
> # Restart firewall whenever the interface comes online.
> case $IFACE in
> eth*) service arno-iptables-firewall restart ;;
> esac
> exit 0
>
> And then remove that from the other script because it will always happen.
> Make sure to 'chmod a+x /etc/network/if-up.d/local-firewall-restart'
> to make the script executable.
>
> #!/bin/sh
> # Call script with sudo.
> ifdown eth1
> modprobe -r cdc_ether
> sleep 1
> modprobe cdc_ether
> ifup eth1
>
> I don't know if any of the above is a critical item. But that is the
> type of thinking I have about it. Hope that helps.
>
> Bob
Yes, I use auto eth0 eth1
I am glad for your improving my scripts, I like it.
I will use one or the other you suggested here.
Many thanks.
--
Tomas Kral <thomas.kral@email.cz>
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