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tcpdump常用命令

监视指定主机的数据包

打印所有进入或离开sundown的数据包.

tcpdump host sundown

也可以指定ip,例如截获所有210.27.48.1 的主机收到的和发出的所有的数据包

tcpdump host 210.27.48.1

打印helios 与 hot 或者与 ace 之间通信的数据包

tcpdump host helios and ( hot or ace )

截获主机210.27.48.1 和主机210.27.48.2 或210.27.48.3的通信

tcpdump host 210.27.48.1 and (210.27.48.2 or 210.27.48.3 )

打印ace与任何其他主机之间通信的IP 数据包, 但不包括与helios之间的数据包.

tcpdump ip host ace and not helios

如果想要获取主机210.27.48.1除了和主机210.27.48.2之外所有主机通信的ip包，使用命令：

tcpdump ip host 210.27.48.1 and ! 210.27.48.2

截获主机hostname发送的所有数据

tcpdump -i eth0 src host hostname

监视所有送到主机hostname的数据包

tcpdump -i eth0 dst host hostname
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pam_unix(sudo:auth): Couldn't open /etc/securetty: No such file or directory

问题来源于raspberry pi4 安装了打印服务，但是cups服务有点异常报，/etc/securetty找不到。
查了下应该是ubuntu 20.04的bug.

root@ubuntu:~# systemctl status cups
● cups.service - CUPS Scheduler
     Loaded: loaded (/lib/systemd/system/cups.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2020-07-01 00:58:26 CST; 12min ago
TriggeredBy: ● cups.path
             ● cups.socket
       Docs: man:cupsd(8)
   Main PID: 8324 (cupsd)
      Tasks: 2 (limit: 4434)
     CGroup: /system.slice/cups.service
             ├─8324 /usr/sbin/cupsd -l
             └─9318 /usr/lib/cups/notifier/dbus dbus://

Jul 01 01:08:15 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:15 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:22 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:22 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:27 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:27 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:29 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:29 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:39 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:39 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory

解决的办法就是新建这个文件/etc/securetty，内容为

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