When logged in I saw: unity kernel: [669168.472431] last sysfs file: /sys/devices/system/cpu/cpu7/cache/index2/shared_cpu_map unity kernel: [669168.475971] Stack: unity kernel: [669168.476634] Call Trace: unity kernel: [669168.477094] Code: 00 48 c7 c3 c0 3c 01 00 49 89 fc 49 89 f5 9c 58 0f 1f 44 00 00 48 89 c2 fa 66 0f 1f 44 00 00 49 89 55 00 49 8b 44 24 08 49 89 de <8b> 40 18 4c 03 34 c5 00 4b ac 81 4c 89 f7 e8 03 36 58 00 49 8b unity kernel: [669168.479444] CR2: 00000000801f0f1d In the log: Mar 1 06:25:04 unity apache2[14216]: [Thu Mar 01 06:25:04 2012] [notice] SIGUSR1 received. Doing graceful restart Mar 1 06:25:04 unity kernel: [669168.471999] BUG: unable to handle kernel paging request at 00000000801f0f1d Mar 1 06:25:04 unity kernel: [669168.472131] IP: [] task_rq_lock+0x4a/0xa0 Mar 1 06:25:04 unity kernel: [669168.472229] PGD 0 Mar 1 06:25:04 unity kernel: [669168.472312] Oops: 0000 [#1] SMP Mar 1 06:25:04 unity kernel: [669168.472431] last sysfs file: /sys/devices/system/cpu/cpu7/cache/index2/shared_cpu_map Mar 1 06:25:04 unity kernel: [669168.472508] CPU 7 Mar 1 06:25:04 unity kernel: [669168.472545] Modules linked in: ipt_MASQUERADE iptable_nat kvm_intel kvm ip6t_LOG xt_hl nf_conntrack_ipv6 nf_defrag_ipv6 ipt_REJECT ipt_LOG xt_limit xt_tcpudp ipt_addrtype xt_state ip6table_filter ip6_tables radeon nf_nat_irc nf_conntrack_irc nf_nat_ftp nf_nat nf_conntrack_ipv4 ipmi_devintf nf_defrag_ipv4 ipmi_watchdog nf_conntrack_ftp psmouse nf_conntrack ttm drm_kms_helper ipmi_si drm ipt able_filter serio_raw joydev i5400_edac edac_core ipmi_poweroff ip_tables ioatdma ipmi_msghandler i5k_amb lp i2c_algo_bit x_tables bridge stp parport shpchp usbhid hid usb_storage uas igb arcmsr dca Mar 1 06:25:04 unity kernel: [669168.474703] Mar 1 06:25:04 unity kernel: [669168.474756] Pid: 1832, comm: apache2 Not tainted 2.6.38-10-server #46~lucid1-Ubuntu Supermicro X7DWU/X7DWU Mar 1 06:25:04 unity kernel: [669168.475004] RIP: 0010:[] [] task_rq_lock+0x4a/0xa0 Mar 1 06:25:04 unity kernel: [669168.475114] RSP: 0018:ffff88040c10fdc8 EFLAGS: 00010082 Mar 1 06:25:04 unity kernel: [669168.475171] RAX: 00000000801f0f05 RBX: 0000000000013cc0 RCX: 0000000000000002 Mar 1 06:25:04 unity kernel: [669168.475245] RDX: 0000000000000282 RSI: ffff88040c10fe20 RDI: 00007f558925f8f0 Mar 1 06:25:04 unity kernel: [669168.475320] RBP: ffff88040c10fde8 R08: 0000000000989680 R09: 000000000000028b Mar 1 06:25:04 unity kernel: [669168.475393] R10: 0000000000007bea R11: 0000000000000001 R12: 00007f558925f8f0 Mar 1 06:25:04 unity kernel: [669168.475467] R13: ffff88040c10fe20 R14: 0000000000013cc0 R15: 0000000000000007 Mar 1 06:25:04 unity kernel: [669168.475542] FS: 00007f5589d03740(0000) GS:ffff8800cfdc0000(0000) knlGS:0000000000000000 Mar 1 06:25:04 unity kernel: [669168.475617] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 Mar 1 06:25:04 unity kernel: [669168.475674] CR2: 00000000801f0f1d CR3: 000000040eb35000 CR4: 00000000000026e0 Mar 1 06:25:04 unity kernel: [669168.475748] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 Mar 1 06:25:04 unity kernel: [669168.475821] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Mar 1 06:25:04 unity kernel: [669168.475895] Process apache2 (pid: 1832, threadinfo ffff88040c10e000, task ffff88040c1f2dc0) Mar 1 06:25:04 unity kernel: [669168.475971] Stack: Mar 1 06:25:04 unity kernel: [669168.476022] 00007f558925f8f0 ffff88040f155ec8 000000000000000f 0000000000000000 Mar 1 06:25:04 unity kernel: [669168.476225] ffff88040c10fe58 ffffffff8105f6dc ffff88040c10fe28 0000000700000286 Mar 1 06:25:04 unity kernel: [669168.476429] 0000000000000003 0000000181a4d7f0 ffff8804015d9850 0000000000000282 Mar 1 06:25:04 unity kernel: [669168.476634] Call Trace: Mar 1 06:25:04 unity kernel: [669168.476689] [] try_to_wake_up+0x3c/0x410 Mar 1 06:25:04 unity kernel: [669168.476747] [] wake_up_process+0x15/0x20 Mar 1 06:25:04 unity kernel: [669168.476806] [] freeary+0x1e0/0x220 Mar 1 06:25:04 unity kernel: [669168.476863] [] T.607+0xb0/0x100 Mar 1 06:25:04 unity kernel: [669168.476921] [] ? vfs_write+0x125/0x190 Mar 1 06:25:04 unity kernel: [669168.476979] [] sys_semctl+0x69/0xa0 Mar 1 06:25:04 unity kernel: [669168.477036] [] system_call_fastpath+0x16/0x1b Mar 1 06:25:04 unity kernel: [669168.477094] Code: 00 48 c7 c3 c0 3c 01 00 49 89 fc 49 89 f5 9c 58 0f 1f 44 00 00 48 89 c2 fa 66 0f 1f 44 00 00 49 89 55 00 49 8b 44 24 08 49 89 de <8b> 40 18 4c 03 34 c5 00 4b ac 81 4c 89 f7 e8 03 36 58 00 49 8b Mar 1 06:25:04 unity kernel: [669168.479300] RIP [] task_rq_lock+0x4a/0xa0 Mar 1 06:25:04 unity kernel: [669168.479391] RSP Mar 1 06:25:04 unity kernel: [669168.479444] CR2: 00000000801f0f1d Mar 1 06:25:04 unity kernel: [669168.479497] ---[ end trace b2b87cfb63915f6c ]--- This happens QUITE OFTEN. Only solution: Sync Filesystem and power cycle (read: I can't reboot, I have to pull the plug! (well, pushing reset button or the same via MagicKey....) Furthermore: Apache in this case will no longer answer, and won't be able to Stop, It goes zombie. The System is still accessible, except for Apache - and Apache can't be braught back to live... Can't say, if it is a memory issue, but note: This is a Server, it has ECC FB-DIMM Memory. Will have to do a memory check some time. But nothing in this regard has been seen in the logs of the daughter board. Some System info: Distributor ID: Ubuntu Description: Ubuntu 10.04.4 LTS Release: 10.04 Codename: lucid *-memory description: System Memory physical id: 16 slot: System board or motherboard size: 16GiB *-bank:0 description: DIMM DDR2 FB-DIMM Synchronous 800 MHz (1.2 ns) vendor: 9801 physical id: 0 serial: 182194CD slot: DIMM1A size: 4GiB width: 64 bits clock: 800MHz (1.2ns) *-bank:1 description: DIMM DDR2 FB-DIMM Synchronous 800 MHz (1.2 ns) [empty] physical id: 1 slot: DIMM1B clock: 800MHz (1.2ns) *-bank:2 description: DIMM DDR2 FB-DIMM Synchronous 800 MHz (1.2 ns) vendor: 9801 physical id: 2 serial: 1921B1FA slot: DIMM2A size: 4GiB width: 64 bits clock: 800MHz (1.2ns) *-bank:3 description: DIMM DDR2 FB-DIMM Synchronous 800 MHz (1.2 ns) [empty] physical id: 3 slot: DIMM2B clock: 800MHz (1.2ns) *-bank:4 description: DIMM DDR2 FB-DIMM Synchronous 800 MHz (1.2 ns) vendor: 9801 physical id: 4 serial: 16213E76 slot: DIMM3A size: 4GiB width: 64 bits clock: 800MHz (1.2ns) *-bank:5 description: DIMM DDR2 FB-DIMM Synchronous 800 MHz (1.2 ns) [empty] physical id: 5 slot: DIMM3B clock: 800MHz (1.2ns) *-bank:6 description: DIMM DDR2 FB-DIMM Synchronous 800 MHz (1.2 ns) vendor: 9801 physical id: 6 serial: 1721CBB7 slot: DIMM4A size: 4GiB width: 64 bits clock: 800MHz (1.2ns) *-bank:7 description: DIMM DDR2 FB-DIMM Synchronous 800 MHz (1.2 ns) [empty] physical id: 7 slot: DIMM4B clock: 800MHz (1.2ns) *-cpu:0 description: CPU product: Intel(R) Xeon(R) CPU E5472 @ 3.00GHz vendor: Intel Corp. physical id: 4 bus info: cpu@0 version: Intel(R) Xeon(R) CPU E5472 @ 3.00GHz slot: LGA771/CPU1 size: 3GHz width: 64 bits clock: 1600MHz capabilities: fpu fpu_exception wp vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx x86-64 constant_tsc arch_perfmon pebs bts rep_good nopl aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca sse4_1 lahf_lm tpr_shadow vnmi flexpriority *-cache:0 description: L1 cache physical id: 6 slot: L1 Cache size: 16KiB capacity: 16KiB capabilities: asynchronous internal write-back *-cache:1 description: L2 cache physical id: 7 slot: L2 Cache size: 12MiB capabilities: burst internal write-back *-cpu:1 description: CPU product: Intel(R) Xeon(R) CPU E5472 @ 3.00GHz vendor: Intel Corp. physical id: 5 bus info: cpu@1 version: Intel(R) Xeon(R) CPU E5472 @ 3.00GHz slot: LGA771/CPU2 size: 3GHz width: 64 bits clock: 1600MHz capabilities: fpu fpu_exception wp vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx x86-64 constant_tsc arch_perfmon pebs bts rep_good nopl aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca sse4_1 lahf_lm tpr_shadow vnmi flexpriority *-cache:0 description: L1 cache physical id: 8 slot: L1 Cache size: 16KiB capacity: 16KiB capabilities: asynchronous internal write-back *-cache:1 description: L2 cache physical id: 9 slot: L2 Cache size: 12MiB capabilities: burst internal write-back