devfs and bpf owner, group, and mode

Lowell Gilbert freebsd-questions-local at
Wed Nov 9 14:28:28 GMT 2005

David Kelly <dkelly at> writes:

> I'm having problems in 5.4 getting automatic ownership and mode correct
> on /dev/bpf2. Added this to /etc/devfs.conf:
> # Allow group tcpdump to use bpf*
> own     bpf0    root:tcpdump
> perm    bpf0    0660
> own     bpf1    root:tcpdump
> perm    bpf1    0660
> own     bpf2    root:tcpdump
> perm    bpf2    0660
> And this to /etc/devfs.rules:
> [devfsrules_bpf=5]
> add path 'bpf*' mode 0660 group tcpdump
> The intent is to allow members of group "tcpdump" to use /dev/bpf2
> without being root. The above creates /dev/bpf[012] as desired at boot
> but some time later /dev/bpf2 disappears.
> System has two NICs, xl0 and fxp0. At this time fxp0 is not being used.
> Vlan0 is configured (as a VLAN of course) on xl0, and thats where I need
> /dev/bpf2 for tcpdump to see what my stuff is doing.
> If missing, /dev/bpf2 is created automatically when tcpdump opens, but
> its not created with the same ownership and mode as during reboot.
> Suspect my problem is related to [devfsrules_bpf=5] or the fact I
> haven't informed the system to apply this rule to the /dev filesystem.

Good guess.  I'm still on my first cup of coffee, and might have taken
a few more minutes to spot that.

> So where is the 'i' that I've failed to dot?

try adding 'devfs_system_ruleset="devfsrules_bpf"' to rc.conf.

To apply it before reboot would be something roughly like 
'devfs /dev ruleset devfsrules_bpf'.  

Lowell Gilbert, embedded/networking software engineer, Boston area

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