trying to run mongoDB off a USB key on ubuntu 14.0.4

I'm trying to set up a mongoDB database on a USB key.
I've mounted my drive like so:

sudo mount /dev/sdb1 /media/usb2

and then I've modified the mongo.conf file to have the following dbpath

dbpath = /media/usb2/mongodb

I've created the mongodb folder on the usb drive.  But what I'm noticing is that the database always fails to start with a permission issue.  Which ... makes sense because it looks like ubuntu mounts the drive under the current user's name.

me@medev:/media/usb3$ ls -lah
total 36K
drwx------ 3 me me  16K Nov 10 16:13 .
drwxr-xr-x 5 root root 4.0K Nov 10 16:08 ..
drwx------ 2 me me  16K Nov 10 16:13 mongodb

And when I try to change the owner, i get an error:

me@medev:/media/usb2$ sudo chown -R mongodb:mongodb .
chown: changing ownership of ‘./mongodb’: Operation not permitted
chown: changing ownership of ‘.’: Operation not permitted
me@medev:/media/usb2$ 

Has anyone tried something like this?  Is this possible on other versions of linux?  I would like to get a prototype of mongoDB on USBs running if at all possible... and on ubuntu.  But I'm willing to consider other distros if there's a high level of confidence that it'll work. 



Perhaps I could try to add the mongod system user to the root group in ubuntu?  Is that a safe thing to do? 
Can you provide me with the required steps? 

Seems you are trying to assing POSIX permissions to a filesystem that is not supported ie fat32, ntfs.

Format your USB Key to a filesystem that support POSIX permissions and try again. (ext4 for example)

using the disk utilities in ubuntu, i formatted my drive to be of type ext4.  

this is what it says when i do an fdisk:

  Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048   968613887   484305920   83  Linux
/dev/sda2       968615934   976771071     4077569    5  Extended
/dev/sda5       968615936   976771071     4077568   82  Linux swap / Solaris

Disk /dev/sdc: 7803 MB, 7803174912 bytes
241 heads, 62 sectors/track, 1019 cylinders, total 15240576 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/sdc doesn't contain a valid partition table

It's the disk in /dev/sdc... 

I've named the drive / file system "mongotest". This is what the permissions look like : 

me@medev:/media/me/mongotest$ ls -lah
total 28K
drwx------  4 me me 4.0K Nov 11 09:05 .
drwxr-x---+ 3 root root 4.0K Nov 11 09:18 ..
drwx------  2 root root  16K Nov 11 09:01 lost+found
drwxr-xr-x  2 root root 4.0K Nov 11 09:05 mongodb
me@medev:/media/me/mongotest$ 

Unfortunately, I still get the permissions error when I try to start mongodb using this filesystem for the database location.  This is what the error in the log looks like:

2014-11-11T09:27:52.635-0500 [initandlisten] allocator: tcmalloc
2014-11-11T09:27:52.635-0500 [initandlisten] options: { config: "/etc/mongod.conf", net: { bindIp: "127.0.0.1" }, storage: { dbPath: "/media/me/mongotest/mongodb" }, systemLog: { destination: "file", logAppend: true, path: "/var/log/mongodb/mongod.log" } }
2014-11-11T09:27:52.635-0500 [initandlisten] exception in initAndListen std::exception: boost::filesystem::status: Permission denied: "/media/me/mongotest/mongodb", terminating
2014-11-11T09:27:52.635-0500 [initandlisten] dbexit: 

Any suggestions on what I might have overlooked? 



I've checked the "mount" command and I can see that the drive is read /write: 

/dev/sdb1 on /media/usb3 type vfat (rw,umask=000)
/dev/sdc on /media/me/mongotest type ext4 (rw,nosuid,nodev,uhelper=udisks2)

Seems something related to permissions : 

2014-11-11T09:27:52.635-0500 [initandlisten] exception in initAndListen std::exception: boost::filesystem::status: Permission denied: "/media/me/mongotest/mongodb", terminating
/media/me/mongotest/mongodb has following permissions :

drwxr-xr-x  2 root root 4.0K Nov 11 09:05 mongodb

So, you can´t write in there, unless you start mongod as root or you change permissions so that others can write in that directory. 

I've added permissions to the folder for the mongod group... like so:

me@medev:~$ sudo setfacl -m g:mongodb:rwx /media/me/mongotest/mongodb

and then to check it worked:

me@medev:~$ getfacl /media/me/mongotest/mongodb/
getfacl: Removing leading '/' from absolute path names
# file: media/jlee/mongotest/mongodb/
# owner: root
# group: root
user::rwx
group::r-x
group:mongodb:rwx
mask::rwx
other::r-x

I think that's supposed to give the mongodb group the access it needs to write the drive....

Just to test whether the ACL permissions are working or not,  I did the following:

1. create a new user in ubuntu called "test".
2. created a new group called testers
3. added test to testers.
4. added testers to ACL list for /media/me/mongotest/mongodb folder on the usb:

 me@medev:~$ getfacl /media/me/mongotest/mongodb/
 getfacl: Removing leading '/' from absolute path names
 # file: media/me/mongotest/mongodb/
 # owner: root
 # group: root
 user::rwx
 group::r-x
 group:mongodb:rwx
 group:testers:rwx
 mask::rwx
 other::r-x

5. Then I changed user to "test":

me@medev:~$ su test
Password:

6. Tried to change directories into the USB key like so:

test@medev:/home/me$ cd /media/me/mongotest
bash: cd: /media/me/mongotest: Permission denied
test@medev:/home/me$ cd /media/me/mongotest/mongodb
bash: cd: /media/me/mongotest/mongodb: Permission denied
test@medev:/home/me$

So it would seem that I'm doing something wrong with the way I'm creating / adding these permissions... because it's failing for both users / groups.

The problem has been resolved.  I had to set the ACL at the /media/me level.

So i did this: 

    setfacl -m g:mongodb:rwx /media/me

I assumed I had to include "mongotest" in the path because that's the name I assigned to the volume / filesystem when I mounted it.  
But I guess that's not the case.  Sorry for all the noise folks.  Hopefully this will help someone else out in the future.