How to check if NAS is mounted via shell script?

koobi · 12-14-2007, 12:13 AM

Hi,
I'm trying to automate a backup process via shell scripts.
I have a NAS box that I use across two machines so I would like to first check if my NAS is mounted via shell.

What's the best way to do this?

Thanks for your time.

chrism01 · 12-14-2007, 12:22 AM

Well, /etc/mtab tells you what is actually mounted, as opposed to /etc/fstab, which tells you what is mounted a boot time.

koobi · 12-14-2007, 12:34 AM

Quote:

Originally Posted by chrism01

Well, /etc/mtab tells you what is actually mounted, as opposed to /etc/fstab, which tells you what is mounted a boot time.

That's fine but I'm not sure what I should grep for.

Code:

# tail -n 1 /etc/mtab 
//nas01.my.box.com/USER-1 /mnt/nas smbfs 0 0 0

would this work:

Code:

cat /etc/mtab | grep -i \/mnt\/nas

or is that insufficient to ensure NAS is mounted?

And how would I use it in an IF condition? I know how to use IF's in terms of structure in a shell script but what would the logical condition itself be?

Thanks for your time.

chrism01 · 12-14-2007, 12:38 AM

Don't use cat, use

Code:

grep -i '/mnt/nas' >/dev/null
if [[ $? -eq 0 ]]
then
    echo "nas mounted"       # your code goes here
fi

bookmark this: http://www.tldp.org/LDP/abs/html/ & http://rute.2038bug.com/index.html.gz

koobi · 12-14-2007, 12:42 AM

Quote:

Originally Posted by chrism01

Don't use cat, use

Code:

grep -i '/mnt/nas' >/dev/null
if [[ $? -eq 0 ]]
then
    echo "nas mounted"       # your code goes here
fi

bookmark this: http://www.tldp.org/LDP/abs/html/ & http://rute.2038bug.com/index.html.gz

But that would only see if the folder /mnt/nas has something in it, right?

If another user happens to copy something to that folder without checking if it was mounted (while NAS is not mounted, hypothetical case), then that condition would result in a false positive, would it not?

Thanks.

chrism01 · 12-14-2007, 01:09 AM

As I said before:
"Well, /etc/mtab tells you what is actually mounted, as opposed to /etc/fstab, which tells you what is mounted a boot time."
Try cat'ing that file then dismount something and cat it again.....

ghostdog74 · 12-14-2007, 01:32 AM

Quote:

Originally Posted by chrism01

Code:

grep -i '/mnt/nas' >/dev/null
.....

missing input filename to grep?

koobi · 12-14-2007, 02:09 AM

Quote:

Originally Posted by chrism01

As I said before:
"Well, /etc/mtab tells you what is actually mounted, as opposed to /etc/fstab, which tells you what is mounted a boot time."
Try cat'ing that file then dismount something and cat it again.....

as i mentioned in my second post, i'm not sure how the IF condition should be written. I need to know what to check for on the IF on the return of the cat of mtab.

unSpawn · 12-14-2007, 02:46 AM

You don't need an IF statement for this.

Code:

echo -n "NAS mounted: "; grep -qi '/mnt/nas' /etc/mtab && echo yes || echo no

koobi · 12-18-2007, 02:17 AM

Quote:

Originally Posted by unSpawn

You don't need an IF statement for this.

Code:

echo -n "NAS mounted: "; grep -qi '/mnt/nas' /etc/mtab && echo yes || echo no

actually i do need an IF condition because I want to do something like this:

Code:

if [ $(grep -qi '/mnt/nas' /etc/mtab) ]; then
    echo 'mounted';
    #do other things here
else
    echo 'NOT mounted';
    #do other things here
fi

but that does not work as expected...it always goes to false.

chrism01 · 12-18-2007, 05:39 PM

That's because grep returns zero (false) if it matches, 1 if no matches, 2 (?) if an error, so reverse your logic.
It'd be clearer if you did the grep on it's own line, then just test the status ($?) in the if [[ ]] eg

Code:

grep -flags string file
if [[ $? -eq 0 ]]
then
    grep matched, do s'thing
else
    no match, do other thing
fi

koobi · 12-27-2007, 01:46 AM

Quote:

Originally Posted by chrism01

That's because grep returns zero (false) if it matches, 1 if no matches, 2 (?) if an error, so reverse your logic.
It'd be clearer if you did the grep on it's own line, then just test the status ($?) in the if [[ ]] eg

Code:

grep -flags string file
if [[ $? -eq 0 ]]
then
    grep matched, do s'thing
else
    no match, do other thing
fi

Thanks.

I had the opportunity to try this out today again (I was assigned to do something else the last few days).

I ran it on another machine, testing if the SATA drive was mounted. When I tested for a mounted SATA drive, it worked fine but when I tested for a non existent SATA drive, the else portion of the condition did not work. I'm assuming it did not work because I didn't see the echo'd message.

Code:

grep -qi \/dev\/sda4 /etc/mtab
if [[ $? -eq 0 ]]
then
    echo 'NAS is mounted. Continuing...';
else
    echo 'NAS is not mounted. Can not continue. Exiting...';
fi

koobi · 12-31-2007, 01:25 AM

Quote:

Originally Posted by koobi

Thanks.

I had the opportunity to try this out today again (I was assigned to do something else the last few days).

I ran it on another machine, testing if the SATA drive was mounted. When I tested for a mounted SATA drive, it worked fine but when I tested for a non existent SATA drive, the else portion of the condition did not work. I'm assuming it did not work because I didn't see the echo'd message.

Code:

grep -qi \/dev\/sda4 /etc/mtab
if [[ $? -eq 0 ]]
then
    echo 'NAS is mounted. Continuing...';
else
    echo 'NAS is not mounted. Can not continue. Exiting...';
fi

Does anyone know why my else doesn't work?

archtoad6 · 01-12-2008, 10:07 AM

This is very puzzling, I tested your code by pasting it into a shell & it worked fine.

I tried it on a non-existent SATA (/dev/sda4), & on existent & non-existent PATA (/dev/hda1, /dev/hda4) partitions w/ no problems.

Post the results of:

Code:

grep  /dev/sdan /etc/mtab
grep  /dev/sdam /etc/mtab

where n exists & m doesn't.

Then the results of:

Code:

grep  /mnt/nas /etc/mtab

once w/ the NAS mounted & once w/ it unmounted.