| Code |
Meaning |
| 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:
| Code |
Meaning |
| < |
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 |
Process in D state
If there are a lot of processes in D state in your system, then something is wrong with it.
What is D state and a process state in general? A process in Linux can be in several states: running,
sleeping, etc. Running process runs on a CPU just now, sleeping process waits for its turn on CPU
or for some other event. Using ps command you can obtain information about state of each process in the system: STAT column shows that:
# ps a
PID TTY STAT TIME COMMAND
4975 tty1 Ss+ 0:00 /sbin/mingetty tty1
4976 tty2 Ss+ 0:00 /sbin/mingetty tty2
6202 pts/0 Ss+ 0:01 -bash
10312 pts/1 Ss 0:00 -bash
639 pts/1 R+ 0:00 ps a
First big S stands for Sleeping, R stands for running
("+" means that the process is foreground and small "s" means that the
process is session leader, but it is not relevant for this article).
D state occurs then the process is in uninterruptible
sleep. This state is bad, because you can't do anything with the process
in D state. Fortunately, process normally remains in such state not for
so long. But if you have a heap of D state processes then some logic in
system is disrupt. If that is happening, the very important thing is to
determine where this unlucky sleep occurs. It is easy to do with ps
command with l option. WCHAN column shows the name of the kernel function where the process is sleeping:
# ps axl | grep D
F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND
vass 13478 7.2 0.0 1732 624 pts/1 D+ 17:36 0:00 find ./
http://wiki.preshweb.co.uk/doku.php?id=linux:psflags
http://wiki.openvz.org/Processes_in_D_state