解决tcpdump sudo权限下Permission denied

在新装的ubuntu server上脚本调用了tcpdump的命令进行抓包并保存致本地文件，当使用命令sudo tcpdump -i eth3 -w eth3_dump.pcap 的时候，出现错误：

$ sudo tcpdump -i eth3 -s 0 -w test_eth3.pcap

tcpdump: test_eth3.pcap: Permission denied

本地帐户是有sudo权限的，而且该账户不使用sudo权限能够在该目录创建文件，并没有报错，为何sudo 权限反倒 Permission Denied？

自然，这个问题最好只能是tcpdump出了问题，google 了一下，发现这是Ubuntu系统下的权限管理framework  “AppArmor” 中设置了tcpdump 工作在enforce模式，其不能正常工作于是报错：

$ sudo apparmor_status
apparmor module is loaded.
10 profiles are loaded.
10 profiles are in enforce mode.
   /sbin/dhclient3
   /usr/bin/evince
   /usr/bin/evince-previewer
   /usr/bin/evince-thumbnailer
   /usr/lib/NetworkManager/nm-dhcp-client.action
   /usr/lib/connman/scripts/dhclient-script
   /usr/lib/cups/backend/cups-pdf
   /usr/sbin/cupsd
   /usr/sbin/tcpdump
   /usr/share/gdm/guest-session/Xsession
0 profiles are in complain mode.
1 processes have profiles defined.
1 processes are in enforce mode :
   /usr/sbin/cupsd (1240)
0 processes are in complain mode.
0 processes are unconfined but have a profile defined.

$ sudo vim /sys/kernel/security/apparmor/profiles

/usr/bin/evince-thumbnailer (enforce)
/usr/bin/evince-previewer (enforce)
/usr/sbin/tcpdump (enforce)
/usr/bin/evince (enforce)
/usr/sbin/cupsd (enforce)
/usr/lib/cups/backend/cups-pdf (enforce)
/usr/lib/connman/scripts/dhclient-script (enforce)
/usr/lib/NetworkManager/nm-dhcp-client.action (enforce)
/sbin/dhclient3 (enforce)
/usr/share/gdm/guest-session/Xsession (enforce)

tcpdump不能工作在enforce模式下，于是改为使用complain模式：

$ sudo aa-complain tcpdump
Setting /etc/apparmor.d/usr.sbin.tcpdump to complain mode.

$ sudo apparmor_status
apparmor module is loaded.
10 profiles are loaded.
9 profiles are in enforce mode.
   /sbin/dhclient3
   /usr/bin/evince
   /usr/bin/evince-previewer
   /usr/bin/evince-thumbnailer
   /usr/lib/NetworkManager/nm-dhcp-client.action
   /usr/lib/connman/scripts/dhclient-script
   /usr/lib/cups/backend/cups-pdf
   /usr/sbin/cupsd
   /usr/share/gdm/guest-session/Xsession
1 profiles are in complain mode.
   /usr/sbin/tcpdump
1 processes have profiles defined.
1 processes are in enforce mode :
   /usr/sbin/cupsd (1240)
0 processes are in complain mode.
0 processes are unconfined but have a profile defined.