On Tue, 2007-07-10 at 11:55 +0000, ben lipkowitz wrote:
> recently i was poking around on a shared mainframe and saw that a user was
> running a rather interesting process:
>
> nullogic q8 - Mon06PM 11:57 Hey, I dont look at you...
>
> where normally it would look something like this:
> fenn rc - Mon07PM 0 (pine)
>
> any ideas on how this might have been accomplished?
> hint: sometimes i can get "w" to say "... (zsh)" at the end.
> this is a NetBSD system btw
>
> curiouser and curouser
>
Nah, its "normal". Consider this perl program:
#!/usr/bin/perl
$0="hello there!";
sleep 1000;
run it and then do a ps -ef:
bdwheele 31578 31505 0 08:31 pts/6 00:00:00 hello there!
>From the perlvar manpage, there's a description of what's going on:
$PROGRAM_NAME
$0 Contains the name of the program being executed.
On some (read: not all) operating systems assigning to $0 modi-
fies the argument area that the "ps" program sees. On some
platforms you may have to use special "ps" options or a differ-
ent "ps" to see the changes. Modifying the $0 is more useful
as a way of indicating the current program state than it is for
hiding the program you're running. (Mnemonic: same as sh and
ksh.)
Note that there are platform specific limitations on the maxi-
mum length of $0. In the most extreme case it may be limited
to the space occupied by the original $0.
In some platforms there may be arbitrary amount of padding, for
example space characters, after the modified name as shown by
"ps". In some platforms this padding may extend all the way to
the original length of the argument area, no matter what you do
(this is the case for example with Linux 2.2).
Note for BSD users: setting $0 does not completely remove
"perl" from the ps(1) output. For example, setting $0 to "foo-
bar" may result in "perl: foobar (perl)" (whether both the
"perl: " prefix and the " (perl)" suffix are shown depends on
your exact BSD variant and version). This is an operating sys-
tem feature, Perl cannot help it.
In multithreaded scripts Perl coordinates the threads so that
any thread may modify its copy of the $0 and the change becomes
visible to ps(1) (assuming the operating system plays along).
Note that the view of $0 the other threads have will not change
since they have their own copies of it.
Brian
> /\-/\
> >( o.o )<
> _____> <________fenn_____
> _______________________________________________
> BLUG mailing list
> BLUG@linuxfan.com
> http://mailman.cs.indiana.edu/mailman/listinfo/blug
_______________________________________________
BLUG mailing list
BLUG@linuxfan.com
http://mailman.cs.indiana.edu/mailman/listinfo/blug
