A customer said, "I want you to get packets regularly when the specified time comes." I hurriedly built CentOS 7 as a capture PC (while googled), I will leave the one at that time as a memorandum.

The version of CentOS 7 is as follows

[smatsu@smatsu ~]$ cat /etc/redhat-release
CentOS Linux release 7.7.1908 (Core)

Thing you want to do

I want to perform packet capture at a specified time.

means

Create a shell script to run Wireshark and use Cento S7 standard cron for the scheduling function.

CentOS installation

Details omitted. Set the virtual machine according to the environment. I don't use sound cards, floppies, printers, etc. so I deleted them at this point. This time I installed it with GNOME.

Install Wireshark

Since it is a GUI, add gnome.

$ sudo yum install -y wireshark-gnome

It has entered.

[smatsu@smatsu ~]$ wireshark -v
wireshark 1.10.14 (Git Rev Unknown from unknown)

Check here in the GUI.

If this is left as it is, the interface will not be displayed for general users due to permission issues, so give permission.

$ sudo groupadd wireshark
$ sudo usermod -aG wireshark [user]

Reboot here. 　　 The interface is displayed.

The GUI is just for confirmation, and from here on, we will set it with the CLI.

Create an executable file

First, create a working folder.

$ mkdir pcap
$ cd pcap

Next, create an executable file.

`pcap.sh`


#!/bin/bash

/usr/sbin/tshark -i ens33 -w /home/smatsu/pcap/`date +\%Y\%m\%d`/`date +\%Y\%m\%d_\%H\%M`.pcapng -a duration:600

・ Tshark = Command version Wireshark ・ If you install gnome, it is included. ・ Ens33 = Interface name you want to capture -The file name is stored as "(date) .pcapng" under the date folder. ・ Capture time is 600 seconds 　 Give execute permission.

chmod +x pcap.sh

Scheduling settings

Set up cron to schedule the executable file. Check the status of cron.

[smatsu@smatsu ~]$ systemctl status crond
● crond.service - Command Scheduler
   Loaded: loaded (/usr/lib/systemd/system/crond.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2020-04-21 22:34:28 JST; 8min ago

If it is not enabled here, enable it.

$ systemctl start crond

Edit the command to be executed by crontab.

$ crontab -e
0 6 * * * /usr/bin/mkdir /home/smatsu/pcap/`date +\%Y\%m\%d`   #Create a date folder at 6am every morning
0 7 * * * /home/smatsu/pcap/pcap.sh                            #Execute the capture file at 7 o'clock every morning

*: Save as wq

Check the contents of cron.

[smatsu@smatsu pcap]$ crontab -l
0 6 * * * /usr/bin/mkdir /home/smatsu/pcap/`date +\%Y\%m\%d`
0 7 * * * /home/smatsu/pcap/pcap.sh

Now you can save the packet capture under the date folder every morning.

Execute packet capture at the specified time on CentOS7