Unknow Permissions bit on /dev/video0 device

Asked by wildpossum on 2011-06-11

I am using Ubuntu 10.10 release.

The following are just some of the few devices with a very very strange permission bit appendage.
Have a look at your own Ubuntu 10.10 system and see if you have the same (like) issue.

crw-rw-rw-+ 1 root video 81, 0 2011-06-11 15:43 /dev/video0
crw-rw-rw-+ 1 root video 81, 2 2011-06-11 15:43 /dev/video1
crw-rw-rw-+ 1 root video 81, 4 2011-06-11 15:44 /dev/video2
crw-rw-rw-+ 1 root video 81, 6 2011-06-11 15:44 /dev/video3

crw-rw-rw-+ 1 root root 10, 62 2011-06-12 01:02 /dev/rfkill

brw-rw-rw-+ 1 root cdrom 11, 0 2011-06-12 01:02 /dev/sr0

crw-rw-rw-+ 1 root video 81, 1 2011-06-12 01:02 /dev/vbi0
crw-rw-rw-+ 1 root video 81, 3 2011-06-12 01:02 /dev/vbi1
crw-rw-rw-+ 1 root video 81, 5 2011-06-12 01:02 /dev/vbi2
crw-rw-rw-+ 1 root video 81, 7 2011-06-12 01:02 /dev/vbi3

/dev/dri:
total 0
crw-rw-rw-+ 1 root video 226, 0 2011-06-12 01:02 card0

You will notice that there is a (+) at the end of the normal crw-rw-rw-+ <--- HERE

Other files (devices) within /dev are all OK and maintain the standard permission bits.

Has the Standard changed or has Ubuntu used something itself for whatever. ???
If so there is nothing saying so in "mknod" in info or the man pages.

I need an answer as the /dev/video has some very strange permission issues that don't seem logical at all
that I need to either put aside (because it is not caused by the /dev/video0 permissions but something else
in the applications program (which I bet it is).

Your timely assistance greatly appreciated.
Grahame.

Question information

Language:
English Edit question
Status:
Solved
For:
Ubuntu coreutils Edit question
Assignee:
No assignee Edit question
Solved by:
Ian Ace
Solved:
2011-06-11
Last query:
2011-06-11
Last reply:
2011-06-11
Best Ian Ace (iaculallad) said : #1

The extra (+) character on the permission is placed by the udev (UserDeviceMapper) script. From what I understand, this ensures that all hardwares plugged gets activated for the current user.
This (+) symbol is not permanent as it gets revoked if there's a change of user (logging out/logging in for a different user).

HTH.

Thanks Ian Ace, that solved my question.

From the fine manual:

    http://www.gnu.org/software/coreutils/manual/coreutils.html#What-information-is-listed

    Following the file mode bits is a single character that specifies
    whether an alternate access method such as an access control list
    applies to the file. When the character following the file mode bits
    is a space, there is no alternate access method. When it is a
    printing character, then there is such a method.

    GNU ls uses a '.' character to indicate a file with an SELinux
    security context, but no other alternate access method.

    A file with any other combination of alternate access methods is
    marked with a '+' character.