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shellsyntaxposixio-redirection

What is /dev/null 2>&1?

I found this piece of code in /etc/cron.daily/apf 

#!/bin/bash  
/etc/apf/apf -f >> /dev/null 2>&1  
/etc/apf/apf -s >> /dev/null 2>&1

It's flushing and reloading the firewall.
I don't understand the >> /dev/null 2>&1 part.

What is the purpose of having this in the cron? It's overriding my firewall rules. Can I safely remove this cron job?

Solution

  • >> /dev/null redirects standard output (stdout) to /dev/null, which discards it.

    (The >> seems sort of superfluous, since >> means append while > means truncate and write, and either appending to or writing to /dev/null has the same net effect. I usually just use > for that reason.)

    2>&1 redirects standard error (2) to standard output (1), which then discards it as well since standard output has already been redirected.