内核线程

Ubuntu 14.04 32bit

先直观地认识一下

ps -eo pid,comm,cmd

  PID COMMAND         CMD
    1 init            /sbin/init
    2 kthreadd        [kthreadd]
    3 ksoftirqd/0     [ksoftirqd/0]
    5 kworker/0:0H    [kworker/0:0H]
    7 rcu_sched       [rcu_sched]
    8 rcu_bh          [rcu_bh]
    9 migration/0     [migration/0]
   10 watchdog/0      [watchdog/0]
   11 watchdog/1      [watchdog/1]
   12 migration/1     [migration/1]
   13 ksoftirqd/1     [ksoftirqd/1]
   15 kworker/1:0H    [kworker/1:0H]
   16 khelper         [khelper]
   17 kdevtmpfs       [kdevtmpfs]
   18 netns           [netns]
   19 writeback       [writeback]
   20 kintegrityd     [kintegrityd]
   21 bioset          [bioset]
   23 kblockd         [kblockd]
   24 ata_sff         [ata_sff]
   25 khubd           [khubd]
   26 md              [md]
   27 devfreq_wq      [devfreq_wq]
   30 khungtaskd      [khungtaskd]
   31 kswapd0         [kswapd0]
   32 ksmd            [ksmd]
   33 khugepaged      [khugepaged]
   34 fsnotify_mark   [fsnotify_mark]
   35 ecryptfs-kthrea [ecryptfs-kthrea]
   36 crypto          [crypto]
   48 kthrotld        [kthrotld]
   50 scsi_eh_0       [scsi_eh_0]
   51 scsi_eh_1       [scsi_eh_1]
   52 scsi_eh_2       [scsi_eh_2]
   53 scsi_eh_3       [scsi_eh_3]
   77 deferwq         [deferwq]
   78 charger_manager [charger_manager]
  127 kpsmoused       [kpsmoused]
  136 jbd2/sda8-8     [jbd2/sda8-8]
  137 ext4-rsv-conver [ext4-rsv-conver]
  266 upstart-udev-br upstart-udev-bridge --daemon
  272 systemd-udevd   /lib/systemd/systemd-udevd --daemon
  378 kvm-irqfd-clean [kvm-irqfd-clean]
  391 hd-audio0       [hd-audio0]
  438 upstart-socket- upstart-socket-bridge --daemon
  536 jbd2/sda1-8     [jbd2/sda1-8]
  537 ext4-rsv-conver [ext4-rsv-conver]
  544 jbd2/sda6-8     [jbd2/sda6-8]
  545 ext4-rsv-conver [ext4-rsv-conver]
  549 jbd2/sda7-8     [jbd2/sda7-8]
  550 ext4-rsv-conver [ext4-rsv-conver]
....
30017 kworker/0:2     [kworker/0:2]
30688 gvfsd-recent    /usr/lib/gvfs/gvfsd-recent --spawner :1.11 /org/gtk/gvfs/exec_spaw/2

第三列中中括号包裹的命令，对应的进程是内核线程。

内核线程是一种特权进程，有如下特点：

1. 以内核态运行在内核地址空间

2. 不与用户直接交互，因此不需要终端设备

3. 在系统启动时创建，然后一直处于活跃的状态直到系统关闭

这些个内核线程对应的proc/$pid/maps文件都是空的...