RHEL 5 Screen Freeze

izzytherocket · 09-21-2010, 09:59 AM

HI,
I am new to Linux and I am having to manage a RHEL 5 server. I am loving the server, except for in the last couple of days the server has completely froze and I am unable to log in at the console nor am I able to connect to it via SSH. Once I force a shut down and restart the server, everything is fine. Where could I look to see what happen to the server? Is there a tool I can use?

Your help would be greatly appreciated!

Izzy

alunduil · 09-21-2010, 10:02 AM

If it's installed you can do a quick analysis using the sar utility. I recommend starting with the following:

Code:

sar -r # Memory usage
sar -q # Load average
sar    # CPU usage

That can let you know if it's a CPU or Memory or neither problem.

Regards,

Alunduil

vinaytp · 09-21-2010, 10:06 AM

Check which process is consuming memory memory and CPU using following command.

By this you can find the CPU intensive application running on your server.

Quote:

# top

izzytherocket · 09-21-2010, 10:18 AM

i don't have sar installed so I wasn't able to show me the results using that command. I was able to see the memory utilization using 'top', and it looks like my main application which is nsm (juniper network security manager) is using most of it.
the screen freezing, is that indication that I don't have enough memory on the server?

Thank you both for responding!

-Izzy

alunduil · 09-21-2010, 10:31 AM

Not necessarily. It simply means that that application is currently using the most memory. What is your swap usage and what is the output of `free -m`? If your swap usage is low and you see lots of processes in the D state you may be thrashing which would indicate that you need more memory or to reduce memory usage on your server.

Regards,

Alunduil

vinaytp · 09-21-2010, 10:34 AM

If you cannot observe the screen. You can execute following command to send 4 interactions of top to a temporary file.

Code:

# top -b -n 4 > temp

Now observe the file temp and find our the intensive applications running.

izzytherocket · 09-21-2010, 10:47 AM

results of 'free -m'
[root@linux log]# free -m
total used free shared buffers cached
Mem: 5692 3059 2632 0 59 1253
-/+ buffers/cache: 1745 3946
Swap: 5535 0 5535

so it looks like I do have enough free memory...

this is the output from running the 'top' command.

top - 16:48:09 up 55 min, 1 user, load average: 0.06, 0.41, 0.57
Tasks: 315 total, 1 running, 314 sleeping, 0 stopped, 0 zombie
Cpu(s): 2.0%us, 0.4%sy, 0.0%ni, 96.2%id, 1.3%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 5828608k total, 3132780k used, 2695828k free, 61884k buffers
Swap: 5668856k total, 0k used, 5668856k free, 1283956k cached

I think I am going to let it run overnight and see what happens in the morning. I will update the thread if I find my Linux box sick! :-)