前两天，缓存系统的一哥们儿在帮忙排查他们超时线程在某个机房占用cpu使用率比较高的情况的时候，用到了
sudo sh -c 'echo w > /proc/sysrq-trigger' ; dmesg
不解，查了下：
dmesg 用来显示系统启动时候的系统信息的，这对系统管理员或者排查问题的时候很重要，参考鸟哥的解释和更详细的资料
sh -c是用sh执行命令
当然，最重要的还是echo w > /proc/sysrq-trigger，查了只知道proc/sysrq-trigger是一个神奇的文件，用echo写一些System Request Key上去，就可以像操作本地计算机一样操纵远程计算机。w呢就是将进入uninterrupted状态的任务的信息dump出来，结果在/var/log/messages里边，输入类似于：
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.482818] SysRq : Show Blocked State
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.486807] task PC stack pid father
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.487382] Sched Debug Version: v0.09, 2.6.32-220.23.2.ali1113.el5.x86_64 #1
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.487385] now at 3277054986.674554 msecs
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.487386] .jiffies : 7571722282
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.487388] .sysctl_sched_latency : 20.000000
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.487390] .sysctl_sched_min_granularity : 4.000000
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.487392] .sysctl_sched_wakeup_granularity : 4.000000
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.487393] .sysctl_sched_child_runs_first : 0.000000
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.487395] .sysctl_sched_features : 3183
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.487397] .sysctl_sched_tunable_scaig 1(oatc<[7143]<[7143]p0200M
Sep 7 22:18:35 hostnameXX.cm10 >24.71 nrng :
Sep 7 22:18:35 hostnameXX.cm10 >24.72 ld :0
Sep 7 22:18:35 hostnameXX.cm10 >24.74 nste :091
Sep 7 22:18:35 hostnameXX.cm10 >24.75 nldpt :130<[7144] rntrtl <[7144] e_lc 774
......
Sep 7 22:18:35 hostnameXX.cm10 >24.78
Sep 7 22:18:35 hostnameXX.cm10 >24.79c_[:<[7149] x_o 4134<[7149] Ivnm 00
Sep 7 22:18:35 hostnameXX.cm10 >24.73 m_ui :9529
Sep 7 22:18:35 hostnameXX.cm10 >24.75 m_ui :.01435784 .rd 000<[7149] pa 82267<[7149] rpaor <[7149] rui <[7149] o <[7149] o_g 00
Sep 7 22:18:35 hostnameXX.cm10 >24.74 ldeo :.00435785 .actb 0435785 .at 0435785 435785 nb s:435785 s I r-yste i erte mx use<[7149]-----------------------------------
Sep 7 22:18:35 hostnameXX.cm10 >24.79
Sep 7 22:18:35 hostnameXX.cm10 >24.79c# 04 z435780 ._nn 0435780 .a 0435780 ._ih 144<[7140] ro_de 06
Sep 7 22:18:35 hostnameXX.cm10 >24.86 nunrpb :
Sep 7 22:18:35 hostnameXX.cm10 >24.87 ntan :5.20435780 .r>d 0435781 .o 356433<[7140] pld] <[7140] pld] <[7140] pld] <[7140] pld] <[7140] pld]
Sep 7 22:18:35 hostnameXX.cm10 4[251.808 ydot 4
Sep 7 22:18:35 hostnameXX.cm10 >24.89 sest <[7140] cdot 82
Sep 7 22:18:35 hostnameXX.cm10 >24.82 .cegd :87
Sep 7 22:18:35 hostnameXX.cm10 >24.83 a_l :00
Sep 7 22:18:35 hostnameXX.cm10 >24.85 tuot :91
Sep 7 22:18:35 hostnameXX.cm10 >24.86 tuol :86
......
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488179] .load_contrib : 0
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488180] .load_tg : 0
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488182]
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488182] runnable tasks:
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488183] task PID tree-key switches prio exec-runtime sum-exec sum-sleep
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488184] ----------------------------------------------------------------------------------------------------------
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488223]
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488223] cpu#7, 2300.408 MHz
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488224] .nr_running : 0
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488225] .load : 0
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488227] .nr_switches : 2890549089
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488228] .nr_load_updates : 701752633
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488230] .nr_uninterruptible : 0
......
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488309] .load_avg : 0.000000
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488310] .load_period : 0.000000
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488312] .load_contrib : 0
Sep 7 22:18:35 hostnameXX.cm10 kernel: : [3275417.488313] .load_tg : 0
......
还有一点sysctl_sched_latency的资料，这里和这里