Can Bash determine if /mnt/place is mounted on?

Cathinfo · 07-30-2007, 04:01 PM

Say you have your typical

/mnt/point

and you want to know if something has been mounted on that point.

How can you do that in a Bash script?

Sometimes you want to know if the directory is "just a directory" or if it refers to an external USB drive, hard drive, etc.

Thanks,

Matthew

unSpawn · 07-30-2007, 04:09 PM

"grep -q /mnt/point /proc/mounts && echo mounted"?

colucix · 07-30-2007, 04:14 PM

The mount command without any argument list all the mounted devices and their mount points, along with other information. You can grep the output from mount to look for a line containing that particular mount point: if it does not exist, nothing is mounted on that location.

EDIT: sorry, posted before viewing the reply from unSpawn. Nice solution!

pwc101 · 07-30-2007, 04:18 PM

Or, /etc/mtab contains information about mounted filesystems, you can grep that too.

ta0kira · 07-30-2007, 04:33 PM

Quote:

Originally Posted by colucix

The mount command without any argument list all the mounted devices and their mount points, along with other information. You can grep the output from mount to look for a line containing that particular mount point: if it does not exist, nothing is mounted on that location.

EDIT: sorry, posted before viewing the reply from unSpawn. Nice solution!

In my experience, /proc/mounts is more useful than the output of mount since mount will just read /etc/mtab, but if / is r/o then new mounts won't be written to it. Also, mount can be called so it doesn't write to /etc/mtab and there is a mount system call which allows programs other than the command proper to mount file systems, which aren't required to update /etc/mtab. Yes, it certainly is a PITA to maintain a system with a r/o root partition, which is why I've stopped doing it, but the point is the kernel itself is a better source of what's mounted.
ta0kira

PS The mount command would be the portable way to check, though. Is there a standard output format across Unixes?

colucix · 07-30-2007, 04:53 PM

Quote:

Originally Posted by ta0kira

...but the point is the kernel itself is a better source of what's mounted.

PS The mount command would be the portable way to check, though. Is there a standard output format across Unixes?

Thank you for the further explanation! Indeed, my use of mount command comes from Unix (SGI and SunOS) where /proc/mount does not exist. By the way, I'm afraid there is not a standard format. Here is an example from SunOS

Code:

/ on /dev/md/dsk/d0 read/write/setuid/intr/largefiles/logging/onerror=panic/dev=1540000 on Tue Jun 26 16:38:06 2007
/proc on /proc read/write/setuid/dev=4a00000 on Tue Jun 26 16:38:03 2007

ta0kira · 07-30-2007, 07:58 PM

Another way:

Code:

if [ "`stat -c%d /`" -ne "`stat -c%d /mnt/cdrom`" ]; then
  echo different file systems
else
  echo same file system
fi

That's GNU stat, BTW. I haven't tried on BSD, but I don't think "normal" stat supports -c.
ta0kira

ta0kira · 07-31-2007, 06:37 PM

On a side note, this problem is an excellent example of why user-mountable devices are by default noexec, nosuid, etc., and why external devices should be mounted with those options, anyway.

What is it you are attempting to prevent/detect? Is this a security or archiving issue, by any chance?
ta0kira

cfaj · 07-31-2007, 07:05 PM

Quote:

Originally Posted by ta0kira

Another way:

Code:

if [ "`stat -c%d /`" -ne "`stat -c%d /mnt/cdrom`" ]; then
  echo different file systems
else
  echo same file system
fi

That's GNU stat, BTW. I haven't tried on BSD, but I don't think "normal" stat supports -c.
ta0kira

There is no normal stat command. There are at least two different versions of the command, and their options (and default output) are dissimilar.

(*BSD stat uses -f for the format option, not -c, and the format specifiers are different.)

cfaj · 07-31-2007, 07:17 PM

Quote:

Originally Posted by Cathinfo

Say you have your typical

/mnt/point

and you want to know if something has been mounted on that point.

How can you do that in a Bash script?

Sometimes you want to know if the directory is "just a directory" or if it refers to an external USB drive, hard drive, etc.

Code:

NL='
'
point=$1  ##  /mnt/point
mnt=`df -P "$point"`
mnt=${mnt#*"$NL"}
case $mnt in
  *"$point") echo "${mnt%% *} is mounted on $point" ;;
  *) echo "Nothing mounted on $point" ;;
esac