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My server hangs and requires a reboot to regain entry

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1. Make sure you are not getting yourself blocked in the firewall. Check /var/log/lfd.log for any blocks at the time of the issue. Also, esnure that there are no cron jobs flushing iptables.

2. Have the physical memory in the server checked and/or swapped out. In our experience, faulty memory is almost always the cause of server hangs. RAM issues can be revealed after our service package work as more memory is excercised with the increased page caching enabled for services such as MySQL to aid performance, and the increased load from some applications, e.g. MailScanner.

3. If you're running a VPS you will need to check whether the server has depeleted its allocated resources.

4. Have the physical disks check out with offline tests and check the disks S.M.A.R.T. settings to see if there are any errors logging against the device, in particular bad blocks. This is the second most common cause of server hangs that we see.

5. You need to have a console connected to your server so that you can observe any errors or messages that are logged to it when the server hangs. this is probably the most important step to take as it is the last ditch place for the kernel to log any problems.

6. At the time of the hang, you need to determing whether you can login to the server console. If so, you can fault find from there.

7. You need to check all of your server logs thoroughly at the time of the hang after it becomes available again. If the kernel is able to write to disk, error messages may be present in the system logs, in particular /var/log/messages

8. If you are seeing failing server daemons, you need to check their respective error logs for the reason

9. You need to check that none of your disk partitions are full and they they have not used up their inode allocation

10. Make sure you're receiving and reading all of your server emails. In particular, any lfd emails regarding server load (PT_LOAD) or add additional recording of server performance (e.g. logging the output from ps or top) on a very frequent basis to try and get a snapshot of what the server is doing as it approaches a hang.

If you are still unable to determine the cause from each of the above steps (some of which you will probably need help with from your server provider), you will most likely need to seek further help from your server provider to perform intensive load tests to help determine what is causing the problem.

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