pidfile is the same when running with -T

[ezbik]

Pid file is the same regardless of interface name , when running with -T :

/run/.pid

Therefore it is impossible to run multiple instances of dhcpcd on different interfaces in test mode.

The bug doesn't exist in Ubuntu 22.04 ( dhcpcd 7.1.0) and appeared in Ubuntu 24.04 ( dhcpcd 10.0.6)

[perkelix]

That's an odd one. Running separate instances of dhcpcd works fine if it's not in test mode. I wonder what test mode does differently to end up with the same PID file. That's clearly a mistake.

[rsmarples]

Why do you want to use test mode on many interfaces? Sounds like what you really want is the --noconfigure option?

[rsmarples]

Also, I can't replicate this at all. When running in test mode a pidfile is never created by dhcpcd.

[ezbik]

Here is how to reproduce. Get a system with 2 network cards, echo them to the stdin of the script.

echo enp0s3 enp0s8 | xargs -n1| xargs -II -P10 -- bash -c 'bash -c "dhcpcd -4 -1 I -T | grep new_ip_ad" 2>&1 | sed "s@^@I==@" '|sort

Output :

enp0s3==DUID 00:01:00:01:2e:b6:24:a4:02:47:5b:32:b6:f2
enp0s3==dhcpcd exited
enp0s3==dhcpcd-10.0.6 starting
enp0s3==enp0s3: IAID 5b:32:b6:f2
enp0s3==enp0s3: leased 10.0.2.15 for 86400 seconds
enp0s3==enp0s3: rebinding lease of 10.0.2.15
enp0s3==new_ip_address='10.0.2.15'
enp0s8==dhcpcd exited
enp0s8==dhcpcd-10.0.6 starting
enp0s8==main: pidfile_lock 1076662: File exists

You see, they started to fight for the same pidfile. And its content is :

root@px24 [~] # cat /run/.pid 
1076662

I need it to simply query DHCP server status on multiple interfaces without configuring them. Unfortunately --noconfigure doesn't output lots of useful info (full dump of the DHCP response).

So the solution would be to include interface name to the pidfile filename when running with -T.

[ezbik]

fixed on my side with unshare -m bash -c "mount -t tmpfs -o size=10M tmpfs /run/; dhcpcd -1 $DEV -T"

[rsmarples]

--configure has all the information in the environment prefixed with _new.
You could write an exit hook to dump this to a file as well if you wanted.
I'm unsure how to replicate this though as in no instance does dhcpcd create a pidfile with -T for me.