Re: Forking as another user
On 03/13/2016 02:14 PM, Peter Scott wrote:
> On Sat, 12 Mar 2016 18:44:18 +0200, Lars Noodén wrote:
[snip]
>> What modification can prevent zombies yet allow multiple concurrent
>> clients to attach?
>
> You need the WNOHANG option on your wait() to make it nonblocking.
Thanks. I've been exploring that and seem to have found out how to make
it work in my case where the program forks children on an ongoing basis
and the parent needs to stay running.
Prior to handling SIGCHLD myself, the $socket->accept() loop was the
outer loop, but returning from the subroutine always caused the loop to
exit. What causes that and how can it be prevented? What I use right
now is another loop around the first loop, but that seems awkward:
sub trap_chld {
waitpid( -1,WNOHANG );
return( 1 );
}
$SIG{CHLD} = \&trap_chld;
...
while ( 1 ) {
while ( my $client_socket = $socket->accept() ) {
...
}
}
exit( 0 );
Regards,
/Lars
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Re: Forking as another user
On Sat, 12 Mar 2016 18:44:18 +0200, Lars Noodén wrote: > The snippet below works to fork as a specific user, if run as root. > However, it generates zombies. The functions wait() or waitpid() seem > to be available to use to stop that, but if I insert either of them in > the outer while loop, only one client can connect at a time. > > What modification can prevent zombies yet allow multiple concurrent > clients to attach? You need the WNOHANG option on your wait() to make it nonblocking. -- Peter Scott http://www.perlmedic.com/ http://www.perldebugged.com/ http://www.informit.com/store/product.aspx?isbn=9780133036268 -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: Forking as another user
Thanks, David and Shlomi (and those that read),
I understand fork() and the style of writing better. Strange that the
defaults for 'use English' are not optimal.
The snippet below works to fork as a specific user, if run as root.
However, it generates zombies. The functions wait() or waitpid() seem
to be available to use to stop that, but if I insert either of them in
the outer while loop, only one client can connect at a time.
What modification can prevent zombies yet allow multiple concurrent
clients to attach?
Regards,
Lars
-
while ( my $client = $server->accept() ) {
$EUID = $priv_sep_uid;
my $pid = fork();
unless ( $pid ) {
print qq(\tforked as $PROCESS_ID\n);
while ( my $input = <$client> ) {
1;
}
exit( 0 );
}
}
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Re: Forking as another user
Hi Lars,
some comments on your code:
On Fri, 11 Mar 2016 20:22:34 +0200
Lars Noodén wrote:
> If I have the code below to fork a child process, how would the right
> way be to fork as a different user? I gather that fork() itself does
> not support that, so some other method must be used.
>
> Regards,
> Lars
>
> -
>
> #!/usr/bin/perl
>
> use strict;
> use warnings;
> use English;# for $UID and such
>
See http://perl-begin.org/tutorials/bad-elements/#non_recommended_regex_vars .
> my $old_uid = $UID;
>
> $UID = 1000;
>
> my $pid = fork();
>
> unless( $pid ){
> print qq(\tThis is a child process, PID $$\n);
> print qq(\tThe child UID is $UID \n);
Here you output trailing whitespace:
http://perl-begin.org/tutorials/bad-elements/#trailing-whitespace
Regards,
Shlomi Fish
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Re: Forking as another user
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256
Hello all.
AFAIK, you can't do that. When you fork everything is copied, including
the UID.
To achieve something similar, you need to launch another process (but
you'll need to be root to launch it as another user)
Regards,
David Santiago
On Fri, 11 Mar 2016 20:22:34 +0200
Lars Noodén wrote:
> If I have the code below to fork a child process, how would the right
> way be to fork as a different user? I gather that fork() itself does
> not support that, so some other method must be used.
>
> Regards,
> Lars
>
> -
>
> #!/usr/bin/perl
>
> use strict;
> use warnings;
> use English;# for $UID and such
>
> my $old_uid = $UID;
>
> $UID = 1000;
>
> my $pid = fork();
>
> unless( $pid ){
> print qq(\tThis is a child process, PID $$\n);
> print qq(\tThe child UID is $UID \n);
>
> sleep 5;
>
> exit 0;
> }
>
> $UID = $old_uid;
>
> print qq(This is the parent process PID $PID and a child PID is
> $pid\n); print qq(The parent is running as UID $UID \n);
>
> sleep 5;
>
> exit 0;
>
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Forking as another user
If I have the code below to fork a child process, how would the right
way be to fork as a different user? I gather that fork() itself does
not support that, so some other method must be used.
Regards,
Lars
-
#!/usr/bin/perl
use strict;
use warnings;
use English;# for $UID and such
my $old_uid = $UID;
$UID = 1000;
my $pid = fork();
unless( $pid ){
print qq(\tThis is a child process, PID $$\n);
print qq(\tThe child UID is $UID \n);
sleep 5;
exit 0;
}
$UID = $old_uid;
print qq(This is the parent process PID $PID and a child PID is $pid\n);
print qq(The parent is running as UID $UID \n);
sleep 5;
exit 0;
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