[CentOS] The relationship between udev and MAKEDEV

Clint Dilks clintd at scms.waikato.ac.nz
Tue Oct 28 04:21:42 UTC 2008

Hi People,

Recently an issue where I was trying to changed the group and permission 
associated with the device /dev/net/tun.  As I knew devices were 
controlled by udev I went looking at its configuration and found this 
rule 50-udev.rules:KERNEL=="tun",                    NAME="net/%k".  
Some research on the web suggested that modifying the default rules was 
a bad idea and that you should in fact override them with your own 
custom rules.  So I tried setting up a custom rule, this failed.  I then 
tried modifying the default rule this also failed.  A helpful response 
from here pointed me to MAKEDEV and I was able to change 
/etc/makedev.d/01linux-2.6.x to do what I wanted.  But this has raised a 
couple of questions for me.

1.  If udev doesn't directly control the creation of this device why is 
there a udev rule for it?
2. Is modifying /etc/makedev.d/01linux-2.6.x likely to cause me issues 
in future ?

My investigation to date has led to me to believe that devices listed in 
/etc/udev/makedev.d/ are the devices that you always want to be present 
on a system rather than relying on something about your systems Hardware 
configuration to lead to a device being created.  Is this correct ?

Thank you for any thoughts / information you can share relating to this.

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