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# 1  
Old 10-04-2012
ping got possessed
Can anyone tell me why my ping got possessed after I ran this command.

Code:
ping google.com & sleep 5 ; kill $!

This is what happened. I hit ctrl+c to end it early. I figured there wouldn't be any problems. Then ping starts back up again and I try to end it again with ctrl+c and it does not work. I finally just open a new tab in my terminal and kill it with the kill command. Why would ctrl+c not work? I thought ctrl+c always works on a foreground process.

Code:
[bob@hi ~]$ ping google.com & sleep 5 ; kill $!
[1] 3095
PING google.com (74.125.229.231) 56(84) bytes of data.
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=1 ttl=55 time=13.7 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=2 ttl=55 time=18.0 ms
^C
[bob@hi ~]$ 64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=3 ttl=55 time=16.8 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=4 ttl=55 time=20.2 ms
^C
[bob@hi ~]$ 64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=5 ttl=55 time=15.7 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=6 ttl=55 time=16.9 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=7 ttl=55 time=15.9 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=8 ttl=55 time=17.3 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=9 ttl=55 time=18.0 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=10 ttl=55 time=15.3 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=11 ttl=55 time=16.5 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=13 ttl=55 time=17.7 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=14 ttl=55 time=13.7 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=15 ttl=55 time=16.9 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=16 ttl=55 time=15.9 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=17 ttl=55 time=16.8 ms
^C
[bob@hi ~]$ 64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=19 ttl=55 time=18.7 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=20 ttl=55 time=14.7 ms
^C
[bob@hi ~]$ ^C
[bob@hi ~]$ ^C
[bob@hi ~]$ ^C
[bob@hi ~]$ ^C
[bob@hi ~]$ ^C
[bob@hi ~]$ ^C
[bob@hi ~]$ 64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=22 ttl=55 time=15.8 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=23 ttl=55 time=14.8 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=24 ttl=55 time=15.7 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=25 ttl=55 time=16.3 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=26 ttl=55 time=15.3 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=27 ttl=55 time=18.8 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=28 ttl=55 time=21.5 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=29 ttl=55 time=15.4 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=30 ttl=55 time=19.1 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=31 ttl=55 time=20.7 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=32 ttl=55 time=17.0 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=33 ttl=55 time=15.9 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=34 ttl=55 time=144 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=35 ttl=55 time=14.8 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=36 ttl=55 time=143 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=37 ttl=55 time=16.7 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=38 ttl=55 time=15.3 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=40 ttl=55 time=14.6 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=41 ttl=55 time=16.3 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=42 ttl=55 time=17.1 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=43 ttl=55 time=16.0 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=44 ttl=55 time=17.0 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=45 ttl=55 time=16.5 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=46 ttl=55 time=17.4 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=47 ttl=55 time=16.2 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=48 ttl=55 time=14.9 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=49 ttl=55 time=17.2 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=50 ttl=55 time=15.8 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=51 ttl=55 time=16.0 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=52 ttl=55 time=15.1 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=53 ttl=55 time=14.2 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=54 ttl=55 time=17.2 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=55 ttl=55 time=19.7 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=56 ttl=55 time=17.8 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=57 ttl=55 time=15.9 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=58 ttl=55 time=17.9 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=59 ttl=55 time=14.8 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=60 ttl=55 time=18.1 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=61 ttl=55 time=17.3 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=62 ttl=55 time=15.4 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=63 ttl=55 time=14.0 ms
64 bytes from mia05s07-in-f7.1e100.net (74.125.229.231): icmp_req=64 ttl=55 time=14.9 ms
^C
[1]+  Killed                  ping google.com
[bob@hi ~]$ 
[bob@hi ~]$ 
[bob@hi ~]$ 
[bob@hi ~]$

# 2  
Old 10-04-2012
In the command line ping google.com & sleep 5 ; kill $!, the & is the command terminator (just like ;). So, first ping google.com is submitted as a background job. Then, the control is passed back to the terminal to execute the line sleep 5 ; kill $!. It seems that you have typed Ctrl-C (after 2 seconds corresponding to the 2 lines of ping output) when this command line was executing so it (the shell) has done what it should do; terminate the foreground process. But, the foreground process was not the ping but the sleep and kill line. So, ping keeps on running in the background, writing periodically to your terminal.
Last edited by elixir_sinari; 10-04-2012 at 04:42 AM..
# 3  
Old 10-04-2012
two proposals to get it to work:
Code:
ping google.com & sleep 5 ; kill %1  #(works in bash with job control)
or
ping google.com & pnr=$!; sleep 5 ; kill $pnr

# 4  
Old 10-04-2012
RudiC, I don't think any of those 2 proposals will work (with INT signal by the user in between). Have you tried these?
Last edited by elixir_sinari; 10-04-2012 at 05:07 AM..
# 5  
Old 10-04-2012
Yes, tested, both work on linux and bash:
Code:
$ ping google.com & pnr=$!; sleep 5 ; kill $pnr
[1] 5233
+ pnr=5233
+ sleep 5
+ ping google.com
PING google.com (173.194.70.102) 56(84) bytes of data.
64 bytes from fa-in-f102.1e100.net (173.194.70.102): icmp_req=1 ttl=50 time=57.5 ms
...
+ kill 5233
$

Code:
$ ping google.com & sleep 5 ; kill %1
[1] 5260
+ sleep 5
+ ping google.com
PING google.com (173.194.70.102) 56(84) bytes of data.
64 bytes from fa-in-f102.1e100.net (173.194.70.102): icmp_req=1 ttl=50 time=59.9 ms
...
+ kill %1
$

I have to admit that it is sensitive to the job no. - if there's more background jobs, %1 won't do.
# 6  
Old 10-04-2012
Even with INT signal (Ctrl-C) by the user after submitting the background job?
# 7  
Old 10-04-2012
Ohhh, got you! You're right, it won't. Tried this, seems better (at least unsusceptible to INT):
Code:
ping google.com & pnr=$!; { sleep 5 ; kill $pnr; } &

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