I have server which hung every 2-5 days. dmesg show following situation: kernel: [490894.231753] INFO: task munin-html:10187 blocked for more than 120 seconds. kernel: [490894.231799] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. kernel: [490894.231843] munin-html D 0000000000000000 0 10187 9796 0x00000000 kernel: [490894.231878] ffff88063174b968 0000000000000082 ffff88063174b8d8 0000000000015b80 kernel: [490894.231930] ffff88063174bfd8 0000000000015b80 ffff88063174bfd8 ffff88062fe644d0 kernel: [490894.231982] 0000000000015b80 0000000000015b80 ffff88063174bfd8 0000000000015b80 kernel: [490894.232033] Call Trace: kernel: [490894.232059] [<ffffffff8117fce0>] ? sync_buffer+0x0/0x50 kernel: [490894.232089] [<ffffffff815a1f13>] io_schedule+0x73/0xc0 kernel: [490894.232115] [<ffffffff8117fd25>] sync_buffer+0x45/0x50 kernel: [490894.232143] [<ffffffff815a258f>] __wait_on_bit+0x5f/0x90 kernel: [490894.232170] [<ffffffff8117fce0>] ? sync_buffer+0x0/0x50 kernel: [490894.232197] [<ffffffff815a2638>] out_of_line_wait_on_bit+0x78/0x90 kernel: [490894.232227] [<ffffffff81080250>] ? wake_bit_function+0x0/0x40 kernel: [490894.232255] [<ffffffff8117fcd6>] __wait_on_buffer+0x26/0x30 kernel: [490894.232288] [<ffffffffa00131be>] squashfs_read_data+0x1be/0x520 [squashfs] kernel: [490894.232320] [<ffffffff8114f0f1>] ? __mem_cgroup_try_charge+0x71/0x450 kernel: [490894.232350] [<ffffffffa0013963>] squashfs_cache_get+0x1c3/0x320 [squashfs] kernel: [490894.232381] [<ffffffffa00136eb>] ? squashfs_copy_data+0x10b/0x130 [squashfs] kernel: [490894.232426] [<ffffffff815a3dbe>] ? _raw_spin_lock+0xe/0x20 kernel: [490894.232454] [<ffffffffa0013b68>] ? squashfs_read_metadata+0x48/0xf0 [squashfs] kernel: [490894.232499] [<ffffffffa0013ae1>] squashfs_get_datablock+0x21/0x30 [squashfs] kernel: [490894.232544] [<ffffffffa0015026>] squashfs_readpage+0x436/0x4a0 [squashfs] kernel: [490894.232575] [<ffffffff8111a375>] ? __inc_zone_page_state+0x35/0x40 kernel: [490894.232606] [<ffffffff8110d072>] __do_page_cache_readahead+0x172/0x210 kernel: [490894.232636] [<ffffffff8110d131>] ra_submit+0x21/0x30 kernel: [490894.232662] [<ffffffff811045f3>] filemap_fault+0x3f3/0x450 kernel: [490894.232691] [<ffffffff812bd156>] ? prio_tree_insert+0x256/0x2b0 kernel: [490894.232726] [<ffffffffa009225d>] aufs_fault+0x11d/0x170 [aufs] kernel: [490894.232755] [<ffffffff8111f6d4>] __do_fault+0x54/0x560 kernel: [490894.232782] [<ffffffff81122f39>] handle_mm_fault+0x1b9/0x440 kernel: [490894.232811] [<ffffffff811286f5>] ? do_mmap_pgoff+0x335/0x380 kernel: [490894.232840] [<ffffffff815a7af5>] do_page_fault+0x125/0x350 kernel: [490894.232867] [<ffffffff815a4675>] page_fault+0x25/0x30 Os info cat /etc/issue.net Ubuntu 10.04.2 LTS uname -a Linux Shard1Host3 2.6.35-32-server #68~lucid1-Ubuntu SMP Wed Mar 28 18:33:00 UTC 2012 x86_64 GNU/Linux This system load via ltsp and hasn't harddrives also it has a lot of memory 24Gb. free -m total used free shared buffers cached Mem: 24152 17090 7061 0 50 494 -/+ buffers/cache: 16545 7607 Swap: 0 0 0 I put vmstat info here but I think it won't give results after reboot vmstat 1 30 procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 0 7231156 52196 506400 0 0 0 0 172 143 7 0 92 0 1 0 0 7231024 52196 506400 0 0 0 0 7859 16233 5 0 94 0 0 0 0 7231024 52196 506400 0 0 0 0 7870 16446 2 0 98 0 0 0 0 7230900 52196 506400 0 0 0 0 7308 15661 5 0 95 0 0 0 0 7231100 52196 506400 0 0 0 0 7960 16543 6 0 94 0 0 0 0 7231100 52196 506400 0 0 0 0 7542 16047 5 1 94 0 3 0 0 7231100 52196 506400 0 0 0 0 7709 16621 3 0 96 0 0 0 0 7231220 52196 506400 0 0 0 0 7857 16552 4 0 96 0 0 0 0 7231220 52196 506400 0 0 0 0 7192 15491 6 0 94 0 0 0 0 7231220 52196 506400 0 0 0 0 7423 15792 5 1 94 0 1 0 0 7231260 52196 506404 0 0 0 0 7686 16296 2 0 98 0 0 0 0 7231260 52196 506404 0 0 0 0 6976 15183 5 0 95 0 0 0 0 7231260 52196 506404 0 0 0 0 7303 15600 4 0 95 0 0 0 0 7231320 52196 506404 0 0 0 0 7967 16241 1 0 98 0 0 0 0 7231444 52196 506404 0 0 0 0 6948 15113 6 0 94 0 0 0 0 7231444 52196 506404 0 0 0 0 7931 16181 6 0 94 0 1 0 0 7231516 52196 506404 0 0 0 0 7715 15829 6 0 94 0 0 0 0 7231516 52196 506404 0 0 0 0 7771 16036 2 0 97 0 0 0 0 7231268 52196 506404 0 0 0 0 7782 16202 6 0 94 0 1 0 0 7231212 52196 506404 0 0 0 0 7457 15622 4 0 96 0 0 0 0 7231212 52196 506404 0 0 0 0 7573 16045 2 0 98 0 2 0 0 7231216 52196 506404 0 0 0 0 7689 16076 6 0 94 0 0 0 0 7231424 52196 506404 0 0 0 0 7429 15650 4 0 95 0 3 0 0 7231424 52196 506404 0 0 0 0 7534 16168 3 0 97 0 1 0 0 7230548 52196 506404 0 0 0 0 8559 15926 7 1 92 0 0 0 0 7230672 52196 506404 0 0 0 0 7720 15905 2 0 98 0 0 0 0 7230548 52196 506404 0 0 0 0 7677 16313 5 0 95 0 1 0 0 7230676 52196 506404 0 0 0 0 7209 15432 5 0 95 0 0 0 0 7230800 52196 506404 0 0 0 0 7522 15861 2 0 98 0 0 0 0 7230552 52196 506404 0 0 0 0 7760 16661 5 0 95 0 In the munin(monitoring system) graphs I see(before server hung): Disk(nbd0) IOs per device: read: 289m but avg by week 2.09m Disk(nbd0) throughput per device: read: 4.73k but avg by week 108.76 Disk(nbd0) utilization per device: 100% but avg by week 1.2% Eth0 traffic was low: in/out only 2Mbps Number of threads increased to 566 usually 392 Fork rate 1.08 but usually 2.82 VMStat(processes state) Increased to 17.77(from 0 as far as I could see in the graph) CPU usage iowait 880.46% when usually 6.67% It'll be great if somebody help me to understand what's up.