Script to BLOCK the ports
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#!/bin/bash
#Block certain outgoing ports
#blockports.sh
iptables -P output ACCEPT
iptables -A output -p tcp -sport portnumbers -j DROP
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Script to OPEN the ports
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#!/bin/bash
#Open outgoing ports
#blockports.sh
iptables -A output -p tcp -sport portnumbers -j ACCEPT
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Entries in crontab (sudo crontab -e)
Run block port script at midnight
Run open port script at noon.
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# m h  dom mon dow   command
0 0 * * * /bin/bash /path/to/script/blockports.sh
0 12 * * * /bin/bash /path/to/script/openports.sh