smk@cbnews.cb.att.com (Stephen M. Kennedy) (02/01/91)
I want to start up a process in the background on a remote machine using remsh (sysV) or rsh (bsd), e.g., remsh/rsh remote-host 'sleep 30 > /dev/null 2>&1 &' and I want the local remote shell command to return immediately. This works if "remote-host" is a sysV machine, but if "remote-host" is a SunOS 4.x (and perhaps this generalizes to bsd-like) machine, the local remsh/rsh won't exit until the remote background command terminates (or the remote rsh daemon is killed by root). On the remote side, ps'ing shows the sleep, a <defunct> process (the remote shell), and the rshd (sleeping on "select" in the kernel). What's going on and is there a workaround? Thanks, Steve Kennedy smk@cbosgd.att.com att!cbosgd!smk
brad@bradley.bradley.edu (Bradley E. Smith) (02/01/91)
In <1991Feb1.125425.14866@cbnews.att.com> smk@cbnews.cb.att.com (Stephen M. Kennedy) writes: >I want to start up a process in the background on a remote machine using >remsh (sysV) or rsh (bsd), e.g., > remsh/rsh remote-host 'sleep 30 > /dev/null 2>&1 &' I had this same problem...what I did was to use a 'C' program below. #include <stdio.h> main() { int i; for (i=0;i<20;i++) { close(i); } i = fork(); if(i) exit(0); execl("/usr/openwin/demo/xterm","bradley", "-ls", "-sb", "-fn","9x15", 0); }
byron@archone.tamu.edu (Byron Rakitzis) (02/02/91)
In article <1991Feb1.145242.16915@bradley.bradley.edu> brad@bradley.bradley.edu (Bradley E. Smith) writes: >In <1991Feb1.125425.14866@cbnews.att.com> smk@cbnews.cb.att.com (Stephen M. Kennedy) writes: > >>I want to start up a process in the background on a remote machine using >>remsh (sysV) or rsh (bsd), e.g., > >I had this same problem...what I did was to use a 'C' program below. > >#include <stdio.h> >main() >{ > int i; > for (i=0;i<20;i++) { > close(i); > } > i = fork(); > if(i) > exit(0); > execl("/usr/openwin/demo/xterm","bradley", "-ls", "-sb", "-fn","9x15", 0); >} You don't really need to write a C program to close file-descriptors; any reasonable shell like sh or rc can do this for you. I have two shell scripts, "rx" and "xr". I type: rx goofy and rx does an rsh to goofy, invoking "xr" with all the necessary arguments. "xr" then takes care to close the stupid file-descriptors (I've found that going up to 9 is sufficient), puts xterm in the background and exits. Here are "rx" and "xr" in their entirety: ------------- #!/usr/arch/bin/rc if (! ~ $#* 1) { echo usage: rx hostname >[1=2] exit 1 } # an rx from a local window will have DISPLAY set to unix:0.0; this must be changed. switch ($DISPLAY) { case unix:* ~ $#hostname 0 && hostname=`hostname display=`{echo $DISPLAY | sed s/unix:/$hostname:/} case * display=$DISPLAY } rsh $1 -n bin/sh/xr $display $1 >/dev/null & ------------- #!/usr/arch/bin/rc -l DISPLAY=$1 xterm -ls -n $2 -title $2 </dev/null >/dev/null >[2] /dev/null <[3=] <[4=] <[5=] <[6=] <[7=] <[8=] <[9=] & # the redirections are a hack to make sure that the rshd knows it can exit ------------- By the way, this "rx", "xr" setup is due to Paul Haahr, who originally wrote these scripts in sh. Byron. -- Byron Rakitzis byron@archone.tamu.edu
smk@cbnews.att.com (Stephen M. Kennedy) (02/02/91)
Looks like you went to the right college :-) brad@bradley.bradley.edu (Bradley E. Smith) writes: >>I want to start up a process in the background on a remote machine using >>remsh (sysV) or rsh (bsd), e.g., > >> remsh/rsh remote-host 'sleep 30 > /dev/null 2>&1 &' >I had this same problem...what I did was to use a 'C' program below. Bingo! This is the shell solution to my particular problem remsh/rsh remote-host 'sleep 30 <&- >&- 2>&- 7>&- &' The offending fd #7 showed up in a "/etc/pstat -u pid-of-sleep-process" in the file section. Thank you, thank you, thank you! Steve Kennedy smk@cbosgd.att.com att!cbosgd!smk
rbj@uunet.UU.NET (Root Boy Jim) (02/02/91)
?In <1991Feb1.125425.14866@cbnews.att.com> smk@cbnews.cb.att.com (Stephen M. Kennedy) writes:
?
?>I want to start up a process in the background on a remote machine using
?>remsh (sysV) or rsh (bsd), e.g.,
?
?> remsh/rsh remote-host 'sleep 30 > /dev/null 2>&1 &'
Try the -n option to rsh.
--
Root Boy Jim Cottrell <rbj@uunet.uu.net>
Close the gap of the dark year in betweenallbery@NCoast.ORG (Brandon S. Allbery KB8JRR) (02/06/91)
As quoted from <1991Feb1.170808.24481@cbnews.att.com> by smk@cbnews.att.com (Stephen M. Kennedy): +--------------- | remsh/rsh remote-host 'sleep 30 <&- >&- 2>&- 7>&- &' | | The offending fd #7 showed up in a "/etc/pstat -u pid-of-sleep-process" in | the file section. +--------------- *7* ????! Was ist los? ++Brandon -- Me: Brandon S. Allbery VHF/UHF: KB8JRR on 220, 2m, 440 Internet: allbery@NCoast.ORG Packet: KB8JRR @ WA8BXN America OnLine: KB8JRR AMPR: KB8JRR.AmPR.ORG [44.70.4.88] uunet!usenet.ins.cwru.edu!ncoast!allbery Delphi: ALLBERY
smk@cbnews.att.com (Stephen M. Kennedy) (02/07/91)
In article <1991Feb6.043021.7019@NCoast.ORG> allbery@ncoast.ORG (Brandon S. Allbery KB8JRR) writes: >As quoted from <1991Feb1.170808.24481@cbnews.att.com> by smk@cbnews.att.com (Stephen M. Kennedy): >+--------------- >| remsh/rsh remote-host 'sleep 30 <&- >&- 2>&- 7>&- &' >| >| The offending fd #7 showed up in a "/etc/pstat -u pid-of-sleep-process" in >| the file section. >+--------------- >*7* ????! Was ist los? Good question. It seems to be a dup of stderr. Also under certain conditions it shows up as fd #6, so now I just close every fd I can (0-9) in the script to be safe. I don't think it's a shell problem, unless it's one shared by both /bin/sh and ksh. Anybody know? Steve Kenndy smk@cbosgd.att.com
eric@mks.mks.com (Eric Gisin) (02/07/91)
>+--------------- >| remsh/rsh remote-host 'sleep 30 <&- >&- 2>&- 7>&- &' >| >| The offending fd #7 showed up in a "/etc/pstat -u pid-of-sleep-process" in >| the file section. >+--------------- >*7* ????! Was ist los? This is a rshd bug. Csh seems to close fd 3-9 at some point. This bug causes lots of wasted time when trying to write an xrsh shell script for X11. You try rsh host "DISPLAY=$DISPLAY $@ 0<>/dev/null 1<&0 2<&0 &" but the rsh doesn't exit after starting the remote command. You have to close fd 0-2 otherwise rshd will wait for them to be closed by the background command ($@ &). But the socket has been dup'd to 6 or 7, so you have to use rsh host "exec 3<&- 4<&- 5<&- 6<&- 7<&- 8<&- 9<&-; DISPLAY=..."