Answers:
我不确定tun0，但是我认为分别在接口打开或关闭时调用/etc/network/if-up.d/和/etc/network/if-down.d/中的脚本。
在脚本内部，您可以根据变量的内容确定哪个接口感兴趣IFACE。
可以肯定的是，添加一个简单的脚本，/etc/network/if-up.d/其中内容是
#!/bin/sh
# filename: tun-up
if [ "$IFACE" = tun0 ]; then
echo "tun0 up" >> /var/log/tun-up.log
fi
使它可执行
sudo chmod +x /etc/network/if-up.d/tun-up
然后查看up事件是否记录在其中 /var/log/tun-up.log
gksudo gedit /etc/network/interfaces
加：
auto tun0
iface tun0 inet manual
up COMMAND
COMMAND可以是命令，例如，ip route add something...或具有可执行权限（chmod +x）的脚本路径，最终存储在中/etc/network/if-up.d/。
相反的up，你可以使用post-up，down，post-down。
说明文件：
IFACE选项
The following "command" options are available for every family and method. Each of these options can be given multiple times in a single stanza, in which case the commands are executed in the order in which they appear in the stanza. (You can ensure a command never fails by suffixing them with "|| true".) pre-up command Run command before bringing the interface up. If this command fails then ifup aborts, refraining from marking the interface as configured, prints an error message, and exits with status 0. This behavior may change in the future. up command post-up command Run command after bringing the interface up. If this command fails then ifup aborts, refraining from marking the interface as configured (even though it has really been configured), prints an error message, and exits with status 0. This behavior may change in the future. down command pre-down command Run command before taking the interface down. If this command fails then ifdown aborts, marks the interface as deconfigured (even though it has not really been deconfigured), and exits with status 0. This behavior may change in the future. post-down command Run command after taking the interface down. If this command fails then ifdown aborts, marks the interface as deconfigured, and exits with status 0. This behavior may change in the future. There exists for each of the above mentioned options a directory /etc/network/if-<option>.d/ the scripts in which are run (with no arguments) using run-parts(8) after the option itself has been processed. Please note that as post-up and pre-down are aliases, no files in the corresponding directories are processed. Please use if- up.d and if-down.d directories instead. All of these commands have access to the following environment variables. IFACE physical name of the interface being processed LOGICAL logical name of the interface being processed ADDRFAM address family of the interface METHOD method of the interface (e.g., static) MODE start if run from ifup, stop if run from ifdown PHASE as per MODE, but with finer granularity, distinguishing the pre- up, post-up, pre-down and post-down phases. VERBOSITY indicates whether --verbose was used; set to 1 if so, 0 if not. PATH the command search path: /usr/local/sbin:/usr/local/bin:��� /usr/sbin:/usr/bin:/sbin:/bin Additionally, all options given in an interface definition stanza are exported to the environment in upper case with "IF_" prepended and with hyphens converted to underscores and non-alphanumeric characters discarded. When ifupdown is being called with the --all option, before doing anything to interfaces, if calls all the hook scripts (pre-up or down) with IFACE set to "--all", LOGICAL set to the current value of --allow parameter (or "auto" if it's not set), ADDRFAM="meta" and METHOD="none". After all the interfaces have been brought up or taken down, the appropriate scripts (up or post-down) are executed.
我曾经systemd在之后运行脚本network-online.target。我的剧本<path>/script.sh。
1.）sudo systemctl edit --force --full my-script.service：
[Unit]
Description=My script after network available
Wants=network-online.target
After=network-online.target
[Service]
Type=simple
User=root
ExecStart=<path>/script.sh
[Install]
WantedBy=multi-user.target
2.） sudo systemctl enable my-script.service
3.） sudo systemctl start my-script.service