Aigner, Thomas wrote:
I did a man on top and sure enough there was a PPID command on
Linux (f then B) for parent process. And yes, they always have the same
parent command. Thanks for your help as I'm obviously still a noob on
Unix.
Nope, that doesn't tell you they're different threads in the same
process -- look at all the obviously different processes whose PPID
(parent PID) is "1" -- "ps -ef | less", the first screenful or so will
all have a PPID of 1. A single process can have lots of different
children and many do.
It does depend on which version you're running, but look for "thread" in
the ps(1) man page. On the system I've got here it says "-m" shows all
threads; 2.4-based machines may show all threads by default (but not
RHEL3, which is closer to 2.6 than 2.4).
Although it's not definitive, finding processes with the exactly the
same memory profile -- same resident set size (RSS), same total size
(SIZE), etc is a bit of a giveaway: any two processes are unlikely to be
using exactly the same amount of memory, any two threads are, by
definition, using the same memory and must show the same statistics
(well, to within stack size, but we can ignore that mostly).
Possibly a good way to look at this is with "top". The "H" key toggles
threads (where it can detect them) and you get plenty good memory
reporting. If you can see all your java threads then you'll see that
they are all suspiciously similar.
Anyway, the reason that you see threads and processes confused is that
there is very little difference between the two in Linux. Indeed, the
lack of distinction caused some problems with the posix thread semantics
that weren't fixed until 2.6 came out. If you're running a 2.6 kernel
then look at /proc/<pid> where <pid> is the PID of the java process.
In that you'll see a sub-directory called "task" which contains
sub-directories for each thread, there's normally only one task, but
multi-threaded processes will have several, eg
$ ps -e | grep java
29918 ? 00:02:38 java
$ ls /proc/29918/task
29918 29920 29922 29924 29928 29930 29937 8993
29919 29921 29923 29925 29929 29934 6875 917
jch
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