New version of /sbin/iptables binary prints nonsense error message when is
called by ordinary non-root user:
iptables v1.8.2 (nf_tables): unknown option "--dport"
Under root user it works correctly and understands --dport argument.
/sbin/iptables binary obviously does not work without root user, so rather
print error message as debugging why /sbin/iptables printed that nonsense
error message about unknown option.
When compiling Testing Linux application, replace syslog() call by
printf(). openlog() does not honor LOG_CONS flag, it works only when
application cannot connect to syslog (which is rare). There is way to force
syslog() call to print to stdout, so replace openlog() and syslog() calls
by normal printf() call via preprocessor macro when compiling Testing Linux
application.
Pali Rohár
Thomas Bernard