Linux server keeps "crashing"

I have a Debian Linux server that has started becoming unavailable/unresponsive as of about 2 weeks ago. In my experience, this is usually caused by a high server load, caused by Apache, a poorly written PHP script, a corrupt database, or sometimes a disk I/O related issue. In this case, though, this doesn't appear to be the case. I installed various utilities to log and warn about high server loads. One example is the sysstat utility. According to these, server load was not the issue.

It was also not a network issue, since, for example, the system log stopped logging at the times the server went down. If it was just a network problem, the system log would have continued to log.

I also couldn't find anything useful in syslog.

Here's an example of what my server load average looked like during the last "crash" (the server went down just after 13:35 or 13:36, and was restarted at 15:14):

# sar -q -f /var/log/sysstat/sa02 -s 13:00:01
Linux 2.6.26-2-686      01/02/13        _i686_

13:05:01      runq-sz  plist-sz   ldavg-1   ldavg-5  ldavg-15
13:15:01            2       153      0.13      0.06      0.01
13:25:02            0       146      0.07      0.18      0.11
13:35:01            3       147      0.12      0.11      0.09
Average:            2       149      0.11      0.12      0.07

15:14:40          LINUX RESTART

15:15:01      runq-sz  plist-sz   ldavg-1   ldavg-5  ldavg-15
15:25:01            2       152      0.14      0.56      0.50
15:35:01            2       152      0.00      0.10      0.26
15:45:01            2       145      0.02      0.11      0.18
15:55:01            1       157      0.10      0.05      0.10
16:05:01            1       156      1.32      0.99      0.48
16:15:01            1       173      0.72      1.09      0.81
16:25:01            2       151      0.10      0.23      0.46
16:35:01            3       145      0.00      0.04      0.24
16:45:01            2       169      0.15      0.61      0.45
16:55:01            2       169      0.18      0.18      0.27
17:05:01            2       161      0.08      0.30      0.30
17:15:01            4       162      0.23      0.31      0.29
17:25:01            2       164      0.03      0.08      0.16
17:35:01            2       165      0.06      0.05      0.09
17:45:01            2       168      0.00      0.02      0.05
17:55:01            2       164      0.03      0.10      0.08
18:05:01            2       168      0.15      0.21      0.13
Average:            2       160      0.19      0.30      0.29

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I'm wondering if someone might be able to help me identify the problem. I realise there could be many possibilities, but a couple of starting points would be good.

Many thanks!
LVL 21
Julian MatzJoint ChairpersonAsked:
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farzanjConnect With a Mentor Commented:
It could also be a hardware issue itself or a filesystem level issue.  Pay attention on the % used of the related file system.   Any issues with hardware?
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Fadi SODAH (aka madunix)Connect With a Mentor Chief Information Security Officer, CISA, CISSP, CFR, ICATE, MCSE, CCNA, CCNP, CCIP, SCSC and SCECommented:
Check the following:
- look in /var/log any suspicious
- do you have free drive space..
- are all the file systems OK? fsck
- memory diagnostic.... could be a bad piece of RAM
- check apache config
- check mysql config it could memory setting bigger than your actual RAM (if you have mysql) if you run mysql
- Apache service starts with no errors??
- check Apache error log if contains hints
..etc

http://httpd.apache.org/dev/debugging.html   
http://www.linuxjournal.com/article/4222
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arnoldConnect With a Mentor Commented:
As others suggest, look in /var/log/messages for a kernel panic.
You need to collect info, memory use, vmstat, iostat, top, and sysstat.
Similar to the sar report.

You can use cacti.net to poll data using snmp
The data collection should be every minute.
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Julian MatzJoint ChairpersonAuthor Commented:
Nothing in logs, but the hardware, bar the hard drive, was replaced, and I haven't had any crashes since. Not sure was the motherboard replaced, actually. I was guessing it could have been the CPU, but I could be wrong; no way to know for sure now, but the main thing is that it's fixed. Thanks for your help/suggestions.
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