trying to run mongoDB off a USB key on ubuntu 14.0.4

[jl]

Hi there.

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.
Thanks.

[jl]

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?
Thanks.

[Jorge Rúa]

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)

Regards.

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[J Lee]

Hi Jorge.

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?

Thanks!

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[J Lee]

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)

[Jorge Rúa]

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.

Regards,

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[J Lee]

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....

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[J Lee]

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.

[J Lee]

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.