On Thu, Nov 28, 2002 at 04:46:07PM +0100, Qian Gong wrote: > Hi, > > I am using CDRDAO to record CDs. I add the user to group cdrom to enable > the access to /dev/scd0 (linked by /dev/cdrom). But I got an error > message 'Cannot map "/dev/cdrom" to a SG device." It seems the user > should have to ability to access /dev/sg0.
Yes, you have to be able to write to sgn to burn CDs. > What's the relationship > between /dev/scd0 and /dev/sg0? Thanks in advance. scd0 is a CD-ROM device that is accessed using SCSI CD-ROM commands. sg0 is what's called a 'generic' SCSI device, where raw commands are sent to the drive. To be able to read a CD, then read access to scd0 should be enough. To write CDs, though, you have to be able to write to sg0 to send the specific commands. A weird thing came up on #debian today, which maybe someone else can explain to _me_: a guy was trying to setup CD ripping with ide-scsi emulation enabled, and had enormous trouble since cdparanoia claimed it couldn't find a generic device. He only had one SCSI device (real and emulated), which was mountable from /dev/scd0, and he had write perms on both scd0 and sg0. In the end, it turned out that he had to have write permissions on 'sg1' as well. Why is that? I was under the impression that sgn was the generic device for scdn, but apparently not... > BTW, cdrdao works well by root. Of course, root has write permissions on sgx. Running cdrdao as a normal might still not work though, since it can't give itself real-time priority, nor lock pages into RAM. You can give it a go though. -rob
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