/dev/cdrom permission issue.

kutty_prasad · 10-14-2007, 06:35 AM

I'm running Slackware 12 and found this issue which happens after every reboot. /dev/cdrom is a soft link to /dev/hdc. By default the permission on this device file is 660. Now, when i run mplayer and access a DVD/VCD I get a error which says "/dev/cdrom not such file or directory" even though the file is present. When i use XINE and access the DVD/VCD, XINE says permission denied on /dev/cdrom. So I changed the permission on /dev/hdc as 666. This solved the problem with mplayer as well. However, when there is a reboot, the permission becomes 660 again. Is there a permanent solution for this?

Thanks.

Alien_Hominid · 10-14-2007, 06:44 AM

You can edit the fstab and use mode=666 value in 4th column.

Franklin · 10-14-2007, 08:17 AM

Did you add yourself to the cdrom group?

Good groups to add oneself to: cdrom, audio, plugdev, video, users(default).

duryodhan · 10-14-2007, 08:42 AM

ok small related question, what about the groups : disk and floppy? should a normal user add himself there too ?

Alien_Hominid · 10-14-2007, 09:26 AM

I personally do not add anything to any of the groups (please enlighten me if I should) and just change permissions where required.

Franklin · 10-14-2007, 09:37 AM

Quote:

Originally Posted by Alien_Hominid

I personally do not add anything to any of the groups (please enlighten me if I should) and just change permissions where required.

That's what the groups are there for.

Runs ls -la on dev for cdrom and look at the device ownerships:

Code:

root@sun:/dev# ls -la | grep cdrom
lrwxrwxrwx  1 root root         3 2007-10-13 20:12 cdrom -> hdc
lrwxrwxrwx  1 root root         3 2007-10-13 20:12 cdrom0 -> hdc
brw-rw----  1 root cdrom  22,   0 2007-10-13 20:12 hdc
root@sun:/dev#

hdc is owned by root but in the cdrom group.
Adding a user to the cdrom group gives the user access to this device.

alisou · 10-14-2007, 09:43 AM

Hi all,

I think of the right way is to add user at group cdrom, not to change permissions of devices. For to add kutty user at cdrom group, type this command under root:

# usermod -G cdrom kutty

and relogin after

edit: if cdrom group do not exist, create it before by this command (under root):
# groupadd cdrom

Alien_Hominid · 10-14-2007, 10:44 AM

So where could I get a list where each group purpose is explained. I found it easier to change permissions than to use groups.

kutty_prasad · 10-15-2007, 06:12 AM

Hi All,

Thanks for the replies.

Alien_Hominid : I will try your suggestion first.

Franklin : I think I missed the "cdrom" group while adding the user. I'll check that.

Thanks.

MQMan · 10-16-2007, 09:40 PM

Run "id" as the user. Most of the groups you need are automatically set for you when the user logs in.

Cheers.

duryodhan · 10-16-2007, 11:51 PM

Forget this ... fixed ... fstab was a little wrong.

Quote:

bash-3.1$ id
uid=1000(<username>) gid=100(users) groups=17(audio),18(video),19(cdrom),81(messagebus),82(haldaemon),83(plugdev),84(power),100(users),1 04(shutdown)

bash-3.1$ ls -la /dev/ | grep cdrom
lrwxrwxrwx 1 root root 3 2007-10-17 12:58 cdrom -> hda
lrwxrwxrwx 1 root root 3 2007-10-17 12:58 cdrom0 -> hda
brw-rw---- 1 root cdrom 3, 0 2007-10-17 12:58 hda

bash-3.1$ mount /dev/cdrom ~/temp
mount: only root can do that
bash-3.1$ mount /dev/hda ~/temp
mount: only root can do that

Shouldn't I be able to mount it if I am in owner group ?

arcanex · 10-16-2007, 11:51 PM

Quote:

Originally Posted by MQMan

Run "id" as the user. Most of the groups you need are automatically set for you when the user logs in.

Cheers.

I've always wondered how the groups are automatically set for users. As far as I can see, I don't have any entry for my username in '/etc/group' (except for my primary GID in '/etc/passwd'), yet 'id' shows me as members of other groups.

Can anyone briefly explain this?

onebuck · 10-17-2007, 07:19 AM

Hi,

Quote:

Originally Posted by arcanex

I've always wondered how the groups are automatically set for users. As far as I can see, I don't have any entry for my username in '/etc/group' (except for my primary GID in '/etc/passwd'), yet 'id' shows me as members of other groups.

Can anyone briefly explain this?

You should look at the '/etc/login.defs' file;

Code:

excerpt from;
~# cat /etc/login.defs |less

# List of groups to add to the user's supplementary group set
# when logging in on the console (as determined by the CONSOLE
# setting).  Default is none.
#
# Use with caution - it is possible for users to gain permanent
# access to these groups, even when not logged in on the console.
# How to do it is left as an exercise for the reader...
#
# Most of these groups are self-explanatory, with the possible
# exception of "plugdev", which allows the use of plugable devices
# such as USB storage (flash memory sticks, most digital cameras,
# some media players, and other devices), many IEEE1394 (sometimes
# called "FireWire") devices, and more.  For plugdev devices, the
# use of HAL is required.  HAL also helps users interact with
# hardware in the other groups below (and other hardware) more
# easily as well, so it's a good idea to turn HAL on for any
# machine that will be used from the console.
#
# Note that users are added to these default groups only when
# logging into a shell with /bin/login, not when using a login
# manager such as kdm.  In that case, users who should have
# hardware access must be added to the appropriate groups
# when the user is added with adduser or useradd, or by editing
# /etc/group directly.
#
CONSOLE_GROUPS          floppy:audio:cdrom:video:plugdev