Uninterruptible sleep

 ps aux

 

dummy 8165 0.0 0.0 2644 1004 pts/1 D+ 23:49 0:00 umount

 

D+？

 

PROCESS STATE CODES
       Here are the different values that the s, stat and state
       output specifiers (header "STAT" or "S") will display to
       describe the state of a process.
       D Uninterruptible sleep (usually IO)
       R    Running or runnable (on run queue)
       S    Interruptible sleep (waiting for an event to complete)
       T    Stopped, either by a job control signal or
            because it is being traced.
       W    paging (not valid since the 2.6.xx kernel)
       X    dead (should never be seen)
       Z    Defunct ("zombie") process, terminated but not
            reaped by its parent.

       For BSD formats and when the stat keyword is used,
       additional characters may be displayed:
       <    high-priority (not nice to other users)
       N    low-priority (nice to other users)
       L    has pages locked into memory (for real-time and custom IO)
       s    is a session leader
       l    is multi-threaded (using CLONE_THREAD, like NPTL pthreads do)
       + is in the foreground process group

In computer operating systems terminology, a sleeping process can either be interruptible (woken via signals) or uninterruptible (woken explicitly). An uninterruptible sleep state is a sleep state that cannot handle a signal (such as waiting for disk or network IO (input/output)).

When the process is sleeping uninterruptibly, the signal will be noticed when the process returns from the system call or trap.

 

A process which ends up in “D” state for any measurable length of time is trapped in the midst of a system call (usually an I/O operation on a device — thus the initial in the ps output).

 

Such a process cannot be killed — it would risk leaving the kernel in an inconsistent state, leading to a panic. In general you can consider this to be a bug in the device driver that the process is accessing.