[gentoo-user] irritating cron habit

[gentoo-user] irritating cron habit

[Philip Webb]

I fetch my mail using a user cron job, as recommended for security.
I also start my Internet connection by hand after logging in:
this is to avoid the jam which arises if it is included in the runlevel
but for some reason the physical Net connection isn't functioning,
when Dhcpcd sits there & can't be killed via Control-C.
Usually, this works very well, but occasionally the cron job runs
before the Dhcpcd command has made the necessary connection
-- it depends on when the start-of-minute falls -- ,
which results in a file  ~/dead.letter , which has to be deleted
(the sequence of commands is clear from the Syslog file).

Is there a way to fix this ? -- I could perhaps write a 2-line script
which would run 'dhcpcd eth0 ; /etc/init.d/vixie-cron',
while removing Vixie-cron from the Default runlevel.

Does anyone have useful suggestions ?

-- 
========================,,============================================
SUPPORT     ___________//___,   Philip Webb
ELECTRIC   /] [] [] [] [] []|   Cities Centre, University of Toronto
TRANSIT    `-O----------O---'   purslowatchassdotutorontodotca

Re: [gentoo-user] irritating cron habit

[Florian Philipp]

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Am 20.02.2011 15:04, schrieb Philip Webb:
> I fetch my mail using a user cron job, as recommended for security.
> I also start my Internet connection by hand after logging in:
> this is to avoid the jam which arises if it is included in the runlevel
> but for some reason the physical Net connection isn't functioning,
> when Dhcpcd sits there & can't be killed via Control-C.
> Usually, this works very well, but occasionally the cron job runs
> before the Dhcpcd command has made the necessary connection
> -- it depends on when the start-of-minute falls -- ,
> which results in a file  ~/dead.letter , which has to be deleted
> (the sequence of commands is clear from the Syslog file).
> 
> Is there a way to fix this ? -- I could perhaps write a 2-line script
> which would run 'dhcpcd eth0 ; /etc/init.d/vixie-cron',
> while removing Vixie-cron from the Default runlevel.
> 
> Does anyone have useful suggestions ?
> 

When dhcpcd runs, there should be the following files:
/var/run/dhcpcd.pid
/var/run/dhcpcd-eth0.pid

Just change your cron job to look like
test -e /var/run/dhcpcd.pid && fetchmail

You can also do something like parsing the output of `/sbin/ifconfig
eth0` with grep -q to see whether it has an ip address so that your cron
job also works when you configure your address statically.
/sbin/ifconfig eth0 | grep -q '\<inet' && fetchmail ...
should do the trick.

Or even more general:
gawk 'BEGIN{found=1} {if(found == 1 && $2 ~ /^0+$/ && $7 ~ /^0+$/)
found=0} END{exit found}' < /proc/net/route && fetchmail

This looks at the routing table and returns 0 when there is a default
route (destination and mask 00000000) no matter over which interface. No
clue whether this works with IPv6.

Hope this helps,
Florian Philipp


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Re: [gentoo-user] irritating cron habit

[Philip Webb]

110220 Florian Philipp wrote:
> Am 20.02.2011 15:04, schrieb Philip Webb:
>> I fetch my mail using a user cron job, as recommended for security.
>> Usually, this works very well, but occasionally the cron job runs
>> before the Dhcpcd command has made the necessary connection
>> which results in a file  ~/dead.letter , which has to be deleted
>> Is there a way to fix this ? -- I could perhaps write a 2-line script
>> which would run 'dhcpcd eth0 ; /etc/init.d/vixie-cron',
>> while removing Vixie-cron from the Default runlevel.
> When dhcpcd runs, there should be the following files:
>   /var/run/dhcpcd.pid       <<-- not this one
>   /var/run/dhcpcd-eth0.pid  <<-- yes
> Just change your cron job to look like
> 'test -e /var/run/dhcpcd.pid && fetchmail'

That's by far the simplest & it still fetches the mail,
so we'll see if it also avoids the occasional internal spam msgs.
Thanks for all the suggestions, which I will add to my Linux notes.

-- 
========================,,============================================
SUPPORT     ___________//___,   Philip Webb
ELECTRIC   /] [] [] [] [] []|   Cities Centre, University of Toronto
TRANSIT    `-O----------O---'   purslowatchassdotutorontodotca

Re: [gentoo-user] irritating cron habit : solved

[Philip Webb]

110220 Philip Webb wrote:
> 110220 Florian Philipp wrote:
>> Just change your cron job to look like
>> 'test -e /var/run/dhcpcd.pid && fetchmail'
> That's by far the simplest & it still fetches the mail,
> so we'll see if it also avoids the occasional internal spam msgs.

Indeed it does: I tried delaying starting the I/net connection
& there is no 'dead.letter' file.  Thanks again.

PS the file is  /var/run/dhcpcd-eth0.pid , not as above.

-- 
========================,,============================================
SUPPORT     ___________//___,   Philip Webb
ELECTRIC   /] [] [] [] [] []|   Cities Centre, University of Toronto
TRANSIT    `-O----------O---'   purslowatchassdotutorontodotca

Re: [gentoo-user] irritating cron habit : solved

[YoYo Siska]

On Mon, Feb 21, 2011 at 12:39:43AM -0500, Philip Webb wrote:
> 110220 Philip Webb wrote:
> > 110220 Florian Philipp wrote:
> >> Just change your cron job to look like
> >> 'test -e /var/run/dhcpcd.pid && fetchmail'
> > That's by far the simplest & it still fetches the mail,
> > so we'll see if it also avoids the occasional internal spam msgs.
> 
> Indeed it does: I tried delaying starting the I/net connection
> & there is no 'dead.letter' file.  Thanks again.
> 
> PS the file is  /var/run/dhcpcd-eth0.pid , not as above.

btw, if I need to check if the network is up in a script, I usually do

ping -q -c1 -w4 some.remote.host >/dev/null 2>&1 && command-to-run-if-remote-host-reachable

It the advantage that it checks directly connection to the host
you wish to connect to, so it also won't run the command if your network
is up, but the remote host is inaccessible...

If your server doesn't respond to pings, just use some other server
(eg google's public dns 8.8.8.8)

The -w4 paramater controls  how long to wait for reply if the network is
up, but the reply is not comming (ie a network problem, if your network
connect is down, ping will return immediately with a "network
unreachable" or "unknown host" error)

yoyo

Re: [gentoo-user] irritating cron habit : solved

[Adam Carter]

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>
> btw, if I need to check if the network is up in a script, I usually do
>
> ping -q -c1 -w4 some.remote.host >/dev/null 2>&1 &&
> command-to-run-if-remote-host-reachable
>
> It the advantage that it checks directly connection to the host
> you wish to connect to, so it also won't run the command if your network
> is up, but the remote host is inaccessible...
>
> If your server doesn't respond to pings, just use some other server
> (eg google's public dns 8.8.8.8)
>


Or you could use hping, which has the advantage that it tests the actual
service you want to use, rather than just the host it sits on;

sphinx adam # hping2 -c 1 -S -p 80 www.google.com >/dev/null 2>&1 && echo
"it worked"
it worked

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