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I upgraded the RAM of my laptop to 4 GB by using two RAM chips with the following specification:

Storage Capacity: 2 GB
Memory Type: DRAM
Technology: DDR2 SDRAM
Form Factor: SO DIMM 200-pin
Memory Speed: 800 MHz (PC2-6400)
Data Integrity Check: Non-ECC
RAM Features: Unbuffered
Supply Voltage: 1.8 V
Compatible Slots: 1 x memory - SO DIMM 200-pin

Since I upgraded my RAM, Ubuntu freezes every once in a while. When Ubuntu freezes, I shutdown down my laptop and reboot using the Ubuntu live CD to check for file sytem errors. Then, I run the fsck program, and it discovers and fixes some file systems errors. Then, I run the badblock program. But, badblocks does not find any problems. I believe the fact that badblocks does not report any problems shows that my hard disk is healthy. And, the filesystem errors seem to be due to the forced shutdowns.

I'm using 64 bits Ubuntu 10.04 lucid with kernel 2.6.32-33-generic.

How can I troubleshoot this problem? How can I find out why my Ubuntu freezes? What log files should I consult? What should I look for in the log files to find the cause of freezes?

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Well, if you suspect the problems started after you installed the new memory, then I would test that memory. You can do that from a live-cd or memory stick. I don't remember if it's available in the boot menu of an installed system. RAM can be bad and bad RAM can cause your system to freeze. If you're using the proprietary driver from ATI, then that's caused freezes here from time to time. But it's difficult to tell what the reason is without more information.

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I tested my RAM's by memtest86 and it didn't report any errors. – reprogrammer Jul 28 '11 at 15:32
My only proprietary driver is "Broadcam STA wireless driver", which is marked as "Tested by Ubuntu developers". – reprogrammer Jul 28 '11 at 15:34
What other information do you need to determine the reason of the freezes? – reprogrammer Jul 28 '11 at 15:34
Have you confirmed that the RAM is causing it by removing it and seeing that it stops crashing? Sometimes it's easy to blaim the wrong thing if two problems arise at the same time. – Jo-Erlend Schinstad Sep 27 '11 at 12:20

If you still have the ram, swap it back out to the old stuff. Test it for a time to see if it freezes. Memtest86 is a wonderful tool, I would recommend letting it run all night long, let it do 3 or more passes.

Also check the hard drive SMART information.

sudo smartctl -a /dev/sda

You can see an overall status with -h rather then -a.

Here is my output. Lines to take note to are, Raw_Read_Error_Rate,Reallocated_Sector_Ct, Seek_Error_Rate. The Pre-fail ones give you the most insight on disk health. If you have any Reallocated_Sector_Ct, its best to look into a new drive. =)

SMART Attributes Data Structure revision number: 16
Vendor Specific SMART Attributes with Thresholds:
  1 Raw_Read_Error_Rate     0x000b   100   100   016    Pre-fail  Always       -       0
  2 Throughput_Performance  0x0005   131   131   054    Pre-fail  Offline      -       148
  3 Spin_Up_Time            0x0007   121   121   024    Pre-fail  Always       -       168 (Average 170)
  4 Start_Stop_Count        0x0012   100   100   000    Old_age   Always       -       165
  5 Reallocated_Sector_Ct   0x0033   100   100   005    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x000b   100   100   067    Pre-fail  Always       -       0
  8 Seek_Time_Performance   0x0005   134   134   020    Pre-fail  Offline      -       28
  9 Power_On_Hours          0x0012   096   096   000    Old_age   Always       -       32368
 10 Spin_Retry_Count        0x0013   100   100   060    Pre-fail  Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       159
192 Power-Off_Retract_Count 0x0032   100   100   000    Old_age   Always       -       915
193 Load_Cycle_Count        0x0012   100   100   000    Old_age   Always       -       915
194 Temperature_Celsius     0x0002   171   171   000    Old_age   Always       -       35 (Lifetime Min/Max 15/41)
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0022   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0008   100   100   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x000a   200   200   000    Old_age   Always       -       0
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