Gfrktyl

I know my CD-ROM device (/dev/sr0) but how can I detect from a script whether the drive is empty or whether there is a disk in it?

You can get information about any block device using the command blkid.

[root@arch32-vm ~]# blkid /dev/sr0

/dev/sr0: UUID="2013-05-31-23-04-19-00" LABEL="ARCH_201306" TYPE="iso9660" PTTYPE="dos"

[root@arch32-vm ~]# echo $?

0

If I remove the disk, I don't get any output and exit value is 2. (0 means success. A non-zero value will typically mean something abnormal happen or an error occurred)

[root@arch32-vm ~]# blkid /dev/sr0

[root@arch32-vm ~]# echo $?

2

Try mounting the device.

mount -t iso9660 /dev/sr0 /mnt/cdrom

Then check the return value $?

If the return is 0, "good" then there was disc present. Else, it will return not good "1" or anything but "0"

So to check silently, I would script it as so.

cdrom_mount=0

mount -t iso9660 /dev/sr0 /mnt/cdrom >/dev/null 2>&1

if [[ $? -gt 0 ]]

    then

    cdrom_mount=true

else

    cdrom_mount=false

fi

This is a very simplistic example, but you could do something similar...

The issue with this shell-scripting approach is that none of the shell commands, mount, lsblk, blkid, can wait/block/pause and determine whether a cdrom is reporting "no medium found" because the tray has just closed and it is initializing itself to read the cd, or because there is no cd in the device, and "no medium found" will be reported forever. So you can choose a reasonable number of tries to pester the cdrom device at a certain sleep interval before giving up, as in the shell script below, or you can write a piece of c code with a few ioctl calls, and get some information from the cdrom, directly through the kernel.

#!/bin/sh



# cd.close

#

# Close the CD-ROM tray, and mount the CD-ROM device:

#

# mount status codes: see man mount(8)

# ------------------------------------

# 0   success

# 1   incorrect invocation or permissions

# 2   system error (out of memory, cannot fork, no more loop devices)

# 4   internal mount bug

# 8   user interrupt

# 16  problems writing or locking /etc/mtab

# 32  mount failure

# 64  some mount succeeded (in the case of mount -a)



CDROM=/dev/sr0

TRIES="1 2 3"

INTERVAL=5

MOUNT=0



TOKENS=( $TRIES )

STOP=${TOKENS[-1]}



for i in $TRIES; do

echo close: ATTEMPT $i of $STOP

output=`mount $CDROM -t iso9660 /cdrom 2>&1`

status=$?

echo mount: OUTPUT $output

echo mount: STATUS $status

if [ $status -eq 0 ]; then

  MOUNT=1

  break

else

  if [[ "$output" =~ "already mounted" ]]; then

    MOUNT=1

    break

  fi

fi

if [ $i -eq $STOP ]; then

  break

fi

echo sleep: $INTERVAL SECONDS...

sleep $INTERVAL

done



if [ $MOUNT -eq 1 ]; then

  echo final: MOUNTED $CDROM

  printf "final: LABEL "

  volname $CDROM

else

  echo final: NO MEDIUM

fi

You can try with lsblk command:

lsblk -fp

If under FSTYPE for line /dev/sr0 there is nothing -> media not loaded into cdrom drive.
If there is something under FSTYPE, probably iso9660 -> media is loaded into cdrom drive.

Another, I think the simplest way:

cat /dev/sr0 | head -1

If output is:

cat: /dev/sr0: No medium found

-> no media loaded.

If output is anything but this:

cat: /dev/sr0: No medium found

-> media is loaded.

Notice: I didn't try this with audio nor empty cds, but I believe result would be the same.

Here is the shell script I use for my own purposes. It's partially based on Allan's answer.

The reasoning behind it is basically that I was using it in an extended shell command using && and needed it to wait for the device to be ready to mount.

#!/bin/bash

# mountdvd:

#   A shell script to wait until the optical drive can be mounted.

#

#   Important Notes:

#    - By default, this will wait about 10 seconds for the drive to finish reading a newly

#      inserted disk.

#    - Works best already be given a mount point in /etc/fstab

#    - Works best if fs type is set to auto

#    - Assumes /etc/fstab allows user to mount device

#

#   Example /etc/fstab listing:

#    /dev/cdrom /media/dvd auto nofail,auto,user,exec,utf8,noatime,ro,uid=plex,gid=pi 0 0



# Command name

COMMAND=`basename $0`



# Device to mount

DVD_DEVICE=/dev/cdrom

MOUNT_POINT=/media/dvd



# Number of attempts before giving up (Total time = ATTEMPTS * WAIT_TIME, default: 10 seconds)

ATTEMPTS=20



# Wait time in seconds

WAIT_TIME=0.5



# Check if already mounted first

MOUTPUT=`mountpoint -q $MOUNT_POINT`

MSTATUS=$?



if [ $MSTATUS -eq 0 ]; then

    echo "$COMMAND: $DVD_DEVICE was already mounted."

    exit 0

fi



#for ATTEMPT in {1..$ATTEMPTS}

while [ $ATTEMPTS -gt 0 ];

do

    # Attempt to mount device

    OUTPUT=`mount $DVD_DEVICE 2>&1`

    STATUS=$?



    if [ $STATUS -eq 0 ]; then

        # Device mounted

        exit 0

    else

        # Double check here, just in case earlier check failed.

        if [[ "$OUTPUT" =~ "already mounted" ]]; then

            # Device was already mounted

            echo "$COMMAND: $DVD_DEVICE was already mounted."

            exit 0

        fi

    fi



    if [ $ATTEMPTS -ne 1 ]; then

        # Wait a moment before trying again.

        sleep $WAIT_TIME

    fi



    let ATTEMPTS=ATTEMPTS-1

done



echo "$COMMAND: ERROR: Unable to mount $DVD_DEVICE."

exit 1

You can do the following with Python3 and the standard library:

import fcntl

import os



CDROM_DRIVE = '/dev/sr0'



def detect_tray(CDROM_DRIVE):

    """detect_tray reads status of the CDROM_DRIVE.

    Statuses:

    1 = no disk in tray

    2 = tray open

    3 = reading tray

    4 = disk in tray

    """

    fd = os.open(CDROM_DRIVE, os.O_RDONLY | os.O_NONBLOCK)

    rv = fcntl.ioctl(fd, 0x5326)

    os.close(fd)

    print(rv)