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echo "1" > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o $EXT_IFACE -j MASQUERADE

This one-liner will identify files containing a string, and then use some bash string manipulation to generate a wildcard for the pair of files sendmail creates for each message (dfn for message content, and Qfn for headers). This assumes you’re running it in the mail queue directory (/var/spool/mqueue for example).


for f in `grep -l -i viagra *`; do t=${f:10:6}; rm -f *${t}; done


The ${f:10:6} extracts the last 6 characters of the filename, then the rm command prepends that with the wildcard.

Some sample output:


[root@mail mqueue]# grep -l -i cialis *
dfn7U8Rc3X020530
dfn7UD7BUh015512
dfn7VELCbV031687


But there are actually six files:


[root@mail mqueue]# ls -l | egrep "020530|015512|031687"
-rw------- 1 root smmsp 2062 Aug 30 01:27 dfn7U8Rc3X020530
-rw------- 1 root smmsp 2232 Aug 30 06:07 dfn7UD7BUh015512
-rw------- 1 root smmsp 2069 Aug 31 07:21 dfn7VELCbV031687
-rw------- 1 root smmsp 825 Aug 30 01:27 Qfn7U8Rc3X020530
-rw------- 1 root smmsp 837 Aug 30 06:07 Qfn7UD7BUh015512
-rw------- 1 root smmsp 810 Aug 31 07:21 Qfn7VELCbV031687


So we run the command, using cialis:


for f in `grep -l -i cialis *`; do t=${f:10:6}; rm -f *${t}; done


Then there are no more files


[root@mail mqueue]# for f in `grep -l -i cialis *`; do t=${f:10:6}; rm -f *${t}; done
[root@mail mqueue]# grep -l -i cialis *
[root@mail mqueue]#


A quick one-liner to show the IP addresses with an established connection to your server, sorted in order:

netstat -ant | grep ESTABLISHED | awk '{print $5}' | awk -F: '{print $1}' | sort | uniq -c | sort -nr

If you care only about a certain TCP port, say 80 for web traffic, the command becomes:

netstat -ant | grep :80 | grep ESTABLISHED | awk '{print $5}' | awk -F: '{print $1}' | sort | uniq -c | sort -nr

Output would look like:


36 14.21.23.10
8 14.21.23.107
7 14.21.23.114
6 14.21.2.34
5 14.21.23.108
5 14.21.23.106
5
2 14.21.13.120
1 14.21.2.23
1 14.21.13.147
1 14.21.13.130
1 14.21.13.128
1 14.21.13.122
1 14.21.13.118
1 14.21.13.112

(more…)