bash script help?

[Knute Johnson]

On 11/13/2011 10:15 PM, Nils Kassube wrote:
> Knute Johnson wrote:
>> I've got a bash script that I run in cron.daily to backup some data
>> to a jump drive.  One of the commands in my script is to umount the
>> drive. If I write;
>>
>> if umount /dev/sdb1; then
>>       #do something
>> fi
>>
>> it always does it even if the umount is successful.
>
> You mean: "if it fails"? Well, I can't confirm. Try this as root:
>
> if umount / 2>/dev/null; then echo 1;else echo 0;fi
>
> Here the output is "0", which I would expect. If I replace / with an
> unmountable partition, the output is "1".
>
>
> Nils
>

root at knutejohnson:/home/knute# if umount / 2>/dev/null; then echo 1; 
else echo 0;fi
0

Why does this return success?  The device is busy and can't be 
unmounted.  The unmountable disk /dev/sdc1 returns 0.

root at knutejohnson:/home/knute# if umount /dev/sdc1; then echo 1;else 
echo 0;fi
umount: /dev/sdc1: not found
0


root at knutejohnson:/home/knute# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1             75865184   8764396  63246964  13% /
none                    505520       244    505276   1% /dev
none                    512148         0    512148   0% /dev/shm
none                    512148       992    511156   1% /var/run
none                    512148         0    512148   0% /var/lock

root at knutejohnson:/home/knute# if mount /dev/sdb1 /media/usbdisk; then 
echo 1;else echo 0;fi
1

root at knutejohnson:/home/knute# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1             75865184   8764388  63246972  13% /
none                    505520       244    505276   1% /dev
none                    512148         0    512148   0% /dev/shm
none                    512148       992    511156   1% /var/run
none                    512148         0    512148   0% /var/lock
/dev/sdb1             15618044   7102312   8515732  46% /media/usbdisk

root at knutejohnson:/home/knute# if umount /dev/sdb1; then echo 1;else 
echo 0;fi
1

root at knutejohnson:/home/knute# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1             75865184   8764388  63246972  13% /
none                    505520       244    505276   1% /dev
none                    512148         0    512148   0% /dev/shm
none                    512148       992    511156   1% /var/run
none                    512148         0    512148   0% /var/lock
root at knutejohnson:/home/knute#

Both of the above appear to me to be wrong, they should both be showing 
0 not 1.  Then there is this;

root at knutejohnson:/home/knute# mount /dev/sdb1 /media/usbdisk;echo $?
0
root at knutejohnson:/home/knute# umount /dev/sdb1; echo $?
0
root at knutejohnson:/home/knute# umount /dev/sdb1; echo $?
umount: /dev/sdb1: not mounted
1

root at knutejohnson:/home/knute# mount /dev/sdc1 /media/usbdisk; echo $?
mount: special device /dev/sdc1 does not exist
32

There is something here I don't understand?

Thanks,


-- 

Knute Johnson