Monitoring the TCP ESTABLISHED Connections

The following script tcpConnect.sh uses nestat to record the number of connection as well as the date and the time of the measurement.

cat /usr/local/src/tcpConnet.sh
#!/bin/bash
C=$(/bin/netstat -nt | tail -n +3 | grep ESTABLISHED | wc -l)
D=$(date)
printf "%s %s %s\n" "$C" "||" "$D"

crontab -l
*/5 * * * * /usr/local/src/tcpConnet.sh >> /var/log/tcpConnet.data

tail -5 /var/log/tcpConnet.data
25 || Sat Oct  8 11:10:01 PDT 2016
26 || Sat Oct  8 11:15:01 PDT 2016
23 ||  Sat Oct  8 11:20:01 PDT 2016
23 || Sat Oct  8 11:25:01 PDT 2016
23 || Sat Oct  8 11:30:01 PDT 2016