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I have an irritating problem: redirecting stderr does not work. I get:

iptables: Chain already exists

I can't be bothered to check if a chain exists already (pointless, iptables just throws an error if the chain exists before I flush it in the next step, so why bother checking if it already exists). In order to ignore this, I redirect stderr to /dev/null but this does not seem to work.

In general: how do I:

  1. check which stream is used by a command in bash? is this even possible?

  2. redirect ALL streams output by a command?

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Yikes! layman error: i was redirecting stderr before redirecting stdout: iptables -N droplist 2>&1 >/dev/null iptables: Chain already exists iptables uses stderr on error, "iptables -N droplist >/dev/null 2>&1" works. Nevertheless, the questions still stand I think. – LetMeSOThat4U Jul 8 '13 at 10:42
You might be interested in "netstat -tnlp" – Synthead Jul 24 '13 at 19:45

1 Answer 1

  • what is your iptables command?

  • you can look at /proc/<pid>/fd/ ! there are "pipe" entries with a pid of another command involved in the command chain

  • redirecting all streams in bash according to TFM:

    There are two formats for redirecting standard output and standard error:
    Of the two forms, the first is preferred. This is semantically equivalent to
    >word 2>&1

Stefan K.

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