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I have a little VPS I run apache and a Minecraft server on. I don't ever turn it off, but should I restart it for some reason, IPTables blocks most of my ports, including port 80. I've tried so many different suggestions on fixing this, but with no luck. Also, since the provider is OVH, the support is... lacking.

So, I've created a workaround, which I'm happy with. I created a simple shell script file to open certain ports I need opened on restart (80 and 25565 for now). The important ones such as 21 and 22 are not affected on restart.

The script looks like this:

iptables -I INPUT -p tcp --dport 80 -j ACCEPT
iptables -I INPUT -p udp --dport 80 -j ACCEPT
iptables -I INPUT -p tcp --dport 25565 -j ACCEPT
iptables -I INPUT -p udp --dport 25565 -j ACCEPT
/sbin/service iptables save

When I manually run it by typing /iptdef.sh, it runs fine, the ports become open and it's all good.

Of course, it's not practical having to remember to run it every time I restart the server, so I added a crontab. The problem is, it doesn't work/run. This is my crontab file:

*/5 * * * * /backup2.sh
*/55 * * * * /backup3.sh
@reboot /iptdef.sh
* * * * *  /iptdef.sh

The first two lines work. They are just simple scripts that make a backup of a folder for me. The second two lines are what's not working.

Is there a chance that perhaps it's not possible to run iptables commands from a cron? It sounds silly, but I can't see any other reason for it not to work. The scripts have the correct permissions.

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  • Are the scripts being run as root (basically, are they in root's crontab)?
    – saiarcot895
    Commented Jul 21, 2015 at 1:50
  • Yes, it is. I even tried giving the script public execution permissions, just in case, but nope, still the same old nothingness.
    – Byonex
    Commented Jul 21, 2015 at 1:55
  • WAIT A SECOND I THINK I FOUND THE PROBLEM
    – Byonex
    Commented Jul 21, 2015 at 1:58
  • Or not - I just realised I missed off the all important #!/bin/bash line at the top of the iptdef.sh file, so I added it, yet still no luck. Give up time soon.
    – Byonex
    Commented Jul 21, 2015 at 2:03

3 Answers 3

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It's because cron forcibly sets PATH to /usr/bin:/bin. You need to invoke iptables as /sbin/iptables or add PATH=/usr/sbin:/sbin:/usr/bin:/bin in your script or crontab. See crontab(5) for details.

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  • 3
    I added PATH=/usr/sbin:/sbin:/usr/bin:/bin to top of the script file and it works perfectly! You, sir, are a gentleman and a scholar and a breeder of fine horses!
    – Byonex
    Commented Jul 21, 2015 at 2:32
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This looks like it is covered well here: crontab's @reboot only works for root? basically the answer depends heavily on what you use for Cron and your Linux distribution.

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  • The issue isn't just that. As you can see, it's also supposed to run every minute too (although it's also running as root anyway)
    – Byonex
    Commented Jul 21, 2015 at 2:02
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I had to add this to /etc/hosts so that mail to anyone at my server's own FQDN would be resolved:

127.0.0.1 mydomain.com.

Notice the dot at the end. In my case, I'm sending email essentially to root@localhost with MAILTO=root which gets translated to [email protected].

Here's some more detail on this answer.

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