Please help with cron hourly

T0MAS · 2009-02-24 17:43:01

I have following script in /etc/cron.hourly
#!/bin/sh
su -l archie -c "ssh -o TCPKeepAlive=no -o ServerAliveInterval=10 -o ExitOnForwardFailure=yes -n -N -T -R 10002:localhost:22 archie@linux.box"

It's doing reverse ssh connection to linux.box, problem I have is that when it runs it doesn't go to the background any my cron.hourly job just stays in the process list:
root 1904 0.0 0.2 2776 1188 ? S 17:01 0:00 /bin/sh /usr/sbin/run-cron /etc/cron.hourly
root 1905 0.0 0.2 2776 1152 ? S 17:01 0:00 /bin/sh /etc/cron.hourly/reverse_ssh
root 1906 0.0 0.1 2200 864 ? S 17:01 0:00 su -l archie -c ssh -o TCPKeepAlive=no -o
archie 1907 0.0 0.4 6072 2480 ? R 17:01 0:00 ssh -o TCPKeepAlive=no -o ServerAliveInterval=10 -o

How do I run reverse_ssh script so that run-cron releases it?
Thanks very much for your help

Regards,
Tomas

brisbin33 · 2009-02-24 18:01:37

#!/bin/sh
su -l archie -c "ssh -o TCPKeepAlive=no -o ServerAliveInterval=10 -o ExitOnForwardFailure=yes -n -N -T -R 10002:localhost:22 archie@linux.box" &
exit 0

right?

T0MAS · 2009-02-24 18:20:59

Thanks, will have a try!

cactus · 2009-02-24 19:36:24

hurrrr!?
Why are you running this in a cron?

I recommend running it under something like daemontools instead (with no-background).
That way if the connection dies, it will auto-restart.

Alternatively (and my recommendation against), add the '-f' flag to ssh to send it to the background in your cron.

T0MAS · 2009-02-25 10:39:37

Hi,
Thanks it works OK with the cron (goes in the background) when I add & and exit 0 to the script.

cactus: I'll try -f option, can you please tell more about daemontools? Where I can get it and where can I read about it?

Cheers,
Tomas

Profjim · 2009-08-25 15:23:41

1. Doing this:

command &
exit 0

will always be the same as doing this:

command &

2. You could include your entire script in the crontab line. But of course you don't need to.

3. Since you're backgrounding the ssh tunnel (whether using '&' or by using the '-f' flag), cron will see the process _it_ started as having completed. So an hour later, it won't refrain from running the job again (it would refrain if the process it started were still running). So you're going to get repeated attempts to open this tunnel, even if it's already open. I guess they'll fail, since port 10002 on your server is already bound to the existing tunnel. But it may generate lots of error output? Are you having the output of your cron jobs mailed to the local owner of the job (this is the default)?

4. If you wanted to keep the tunnel open all the time, and reopen it when it fails, what you're doing is one way to achieve that. If on the other hand you just want the tunnel open for a short time, you could change your ssh line from

ssh -o TCPKeepAlive=no -o ServerAliveInterval=10 -o ExitOnForwardFailure=yes -n -N -T -R 10002:localhost:22 archie@linux.box &

to

ssh -o TCPKeepAlive=no -o ServerAliveInterval=10 -o ExitOnForwardFailure=yes -n -f -T -R 10002:localhost:22 archie@linux.box sleep 10

This replaces the no-command switch "-N" with the command "sleep 10", and uses the "-f" flag instead of "&". It will hold the tunnel open for 10 seconds. If some other process uses the tunnel within 10 seconds, tunnel will continue to stay open until that process (and all other processes) stop using it. You can make the sleep for longer if you like.

Arch Linux

#1 2009-02-24 17:43:01

Please help with cron hourly

#2 2009-02-24 18:01:37

Re: Please help with cron hourly

#3 2009-02-24 18:20:59

Re: Please help with cron hourly

#4 2009-02-24 19:36:24

Re: Please help with cron hourly

#5 2009-02-25 10:39:37

Re: Please help with cron hourly

#6 2009-08-25 15:23:41

Re: Please help with cron hourly

Board footer