if (disk is mounted) unmount if (disk is unmounted) mount

Shell Programming and Scripting
1

Hey there, sorry if this is a bit too much of a noob question, trying to get to grips with a simple bash script - but i have done ZERO bash scripting.

basically having worked out how to mount and unmount disks using:
disktool -m *device* & disktool -e *device*

  • and looking at the result of disktool -l
    i see that from the results each device has a parameter Mountpoint = '/Volumes/My Disk' if the "My Disk" is mounted - or - Mountpoint = '' if unmounted.

Basically I am looking to write a script that looks to see if a partition on my external disk is mounted or not, if it is mounted - then the disk is unmounted - - and if it is unmounted the disk is mounted.

So this this disk is disk1s2. How do I query the Mountpoint and see what the result is?

Basically :

if (disk1s2.Mountpoint == "") {
disktool -m disk1s2
}

if (disk1s2.Mountpoint == "/Volumes/My Disk") {
disktool -e disk1s2
}

^ is obviously very, very, very wrong for a bash script - but you get the gist.

Any help would be greatly appreciated

2

This works on Ubuntu Linux

mountPart=/path/to/part
rootId=$(stat -c%d /)
mountId=$(stat -c%d "${mountPart}")
if (( rootId == mountId ))
then
   # code for not mounted
else
   # code for mounted
fi

Your milage may vary.

Andrew

3

I don't know what is 'disktool'. It's not installed on my CentOS box, therefore I'd like to present a more general solution:
When a filesystem gets mounted, there is a record about it in /etc/mtab.
Each partition of your disk is gonna be represented by a special file /dev/sdb1 or /dev/sdc4, etc.. (sd* for SATA drives, at least).
Now this can change, depending on what devices you have currently plugged in, so it's not good to depend that your disk is always gonna be /dev/sdb1. A reliable way to find out which /dev/sd* is your disk is to find out the UUID of your disk:
Unmount and unplug it and do

ls -l /dev/disk/by-uuid

Then plug it in and issue the same command. You'll see one more entry (my disk is 886C3A4E6C3A3772), that's the uuid of your device. ls -l also shows you that it is a symbolic link to that special file /dev/sd*.
Now let's put all this info together:

#!/bin/bash

device=`ls /dev/disk/by-uuid/886C3A4E6C3A3772 -l | awk -F/ '{print $NF}'`  #find which file in /dev/ is my disk

if [ _"`grep /dev/$device /etc/mtab`" = _ ] ; then
    mounted=0 # there is no record of this device in /etc/mtab
    echo "Device /dev/$device is not mounted"
    mount  /dev/$device /my/mountpoint
else
    mounted=1 # record found => mounted
    echo "Device /dev/$device is mounted"
    umount  /dev/$device
fi

You may need root privileges to do the mounting though.
The disadvantage of this script is that you have to hardcode the UUID of your device in it. To abstract from this, you could
find the device by looking at the last device plugged in. Like this:

device=`ls /dev/disk/by-uuid -ltr | tail -1 | awk -F/ '{print $NF}'`

ls -trl will print the files in long format (-l), sorted by date (-t), in reverse order (-r), so you'll have the last plugged-in device last. tail -1 will grab just the last line of the output of ls command.

Hope this helps.

mounted=1 is just a flag in case you wanted to do some more bash magic outside the if statement