Why are post-up commands in /etc/network/interfaces ran multiple times at boot?

Question

Here is the content of /etc/network/interfaces:

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp

post-up /etc/network/if-up.d/sshstart

And sshstart is a script with the following in it:

curl something something darkside send a file over ftps in the background &
/usr/bin/autossh -M 0 -f -N -o ServerAliveInterval=15 -o ServerAliveCountMax=3 -R 127.0.0.1:2005:127.0.0.1:22 -R 192.168.1.10:2006:192.168.2.110:1912 -L 127.0.0.1:5249:192.168.1.212:5249 [email protected] -p 8080

When the machine reboots, the curl command is executed multiple times, the file ends up 2 or 3 times on the ftp server and when I look at the processes it seems like there are multiple instances of autossh running... Not sure if this is how autossh does things or not, but for sure curl shouldn't upload the file multiple times.

My hunch is that the whole sshstart script is ran multiple times but I don't understand why.

I tried searching for details on the network setup process at boot but all I could find was syntax information for the interfaces file.

Can someone help please?

Thank you.

---Edit---

As suggested bellow I have modified my interfaces file as follow (removed the empty lines above post-up):

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp
post-up /etc/network/if-up.d/sshstart

And added the following line to sshstart:

echo $(date)>>/run/shm/sshstart.log

Here is the content of /run/shm/sshstart.log after a reboot:

Wed Oct 29 08:07:00 EDT 2014
Wed Oct 29 08:07:07 EDT 2014
Wed Oct 29 08:07:07 EDT 2014
Wed Oct 29 08:07:07 EDT 2014

So its been ran 4 times :( what's going on?

Answer 1

Files in /etc/network/if-up.d already run automatically whenever an interface (any interface) comes up. When you specify the same script to run again in an explicit post-up command, you only cause the script to run again. So my guess is this is what should happen:

• It runs once when lo comes up (with environment variable IFACE=lo) due to being located in /etc/network/if-up.d.
• It runs once when eth0 comes up (with environment variable IFACE=eth0) for the same reason.
• It runs again when eth0 comes up (with environment variable IFACE unset) because you asked for this in a post-up directive.

I'm not sure where the fourth time comes from, but anyway that's three already.

You need to either locate the script somewhere else and run it once using a post-up directive, or leave it where it is but don't mention it in a post-up directive and check the value of $IFACE so that it does nothing unless the desired interface (eth0) has come up.

Answer 2

As stated by Celada, /etc/network/if-up.d scripts are run for each interface. To avoid rule duplication simply add:

[ "$IFACE" = "eth0" ] || exit 0

at the top of your script. This will cause the script to exit immediately if the interface is not the desired one.

Answer 3

Scripts in /etc/network/if-*.d are run for each interface, but also for each address family (IPv4 and IPv6).

You can check the variable $ADDRFAM if you don't want or need tĥe script to run for both IPv4 and IPv6 families.

For example, if you only need your script to run for a specific interface and only for it's IPv4 address, you could start with something like this:

[ "$IFACE"   = "eth0" ] || exit 0  # we only want interface "eth0"
[ "$ADDRFAM" = "inet" ] || exit 0  # we only want IPv4 (not "inet6" for IPv6)

Answer 4

Delete empty line before post-up-command. This should relate the post-up command to eth0 only. Additionally move your script out of if-up.d folder. Scripts in that folder are executed automatically, no matter if defined as post-up. In your case it will run additionally to your post-up-command.