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Home > Archive > Unix administration > July 2004 > question for a column of ps reporting
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question for a column of ps reporting
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| Alex Shi 2004-07-21, 2:48 am |
| Hi,
What does WCHAN mean in ps reporting? In this column, what does
"schedu" mean? Why a process is set to "schedu" or just "-"?
Alex
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| Doug Freyburger 2004-07-21, 5:58 pm |
| Alex Shi wrote:
>
> What does WCHAN mean in ps reporting? In this column, what does
> "schedu" mean? Why a process is set to "schedu" or just "-"?
Did you try reading the man page? Here's the exerpt from AIX:
WCHAN
(-l flag) The event for which the process or kernel thread is waiting or
sleeping. For a kernel thread, this field is blank if the kernel thread is
running. For a process, the wait channel is defined as the wait channel of the
sleeping kernel thread if only one kernel thread is sleeping; otherwise a star
is displayed.
WCHAN
(l flag) The event on which process is waiting (an address in the system). A
symbol is chosen that classifies the address, unless numerical output is
requested.
So it's what the thread is waiting for. Looks like you chose the
option to classify the address to get "schedu". Your vendor's
man page should define that but my best guess is it means the
thread is runable and waiting to get scheduled some runtime.
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| John DuBois 2004-07-21, 5:58 pm |
| In article <tZlLc.10276$OD2.4249@nntp-post.primus.ca>,
Alex Shi <chpshi@stonix.com> wrote:
>What does WCHAN mean in ps reporting?
That's the "wait channel". When a process requests some service from the
kernel that can't be satisfied immediately (for example, input from a tty, a
block from some file that must be read from disk, or even an explicit request
to sleep for a while), it is put to sleep. Whatever puts the process to sleep
(a driver or some other part of the kernel) selects an address to use as a
"tag" for the event that will eventually wake it up. When the event occurs,
any processes waiting on that address will be waked up.
> In this column, what does "schedu" mean? Why a process is set to "schedu"
> or just "-"?
If there's no wait channel, the process is in some state other than waiting on
an event at its own request. It might be running, suspended, in the process of
being created or destroyed, waiting for blocks of its executable to be paged
in, running under a debugger, etc.
John
--
John DuBois spcecdt@armory.com KC6QKZ/AE http://www.armory.com/~spcecdt/
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