Hi

Can we have directory quota on Linux

Disk quota at least, so I guess it's what you're asking, right?

In linux we have user & group quota

can we also have quota only for directory which only look for users 0r group space

But will only refer to directory

Quota is based upon filesystems, but you can always create a virtual filesystem and mount it on a specific (empty) directory with the usrquota and/or grpquota flags. In steps this will be:
1. create the mount point
2. create a file full of /dev/zero, large enough to the maximum size you want to reserve for the virtual filesystem
3. format this file with an ext3 filesystem (you can format a disk space even if it is not a block device, but double check the syntax of every - dangerous - formatting command)
4. mount the newly formatted disk space in the directory you've created as mount point, e.g.
5. Set proper permissions
6. Set quotas
and the trick is done.

To answer your question, you could have a quota on a specific directory, but you would need to create a new partition specifically for that directory. Otherwise, the quotas apply to users and groups on a specific volume.

(someone correct me if I'm wrong)

Actually the filesystem with quota can be either a block device (like a partition) or a reserved disk space (pseudo-device). If you don't want to re-partition the hard disk, the latter can be a solution.

Thankal for your solution i will try it but i have one more query regarding the same

Once the virtual filesystem is created after that can i increase the size of filesystem.

Yes. Once I increased the size of a virtual filesystem on a Fedora Core 5 machine and never experienced any problem with it. I had a filesystem of 150 Mb in /usr/virtual-disk/data.ext3 and I mounted it on /data. The following commands worked for me
I doubled the size of the filesystem and no data was lost. Anyway, better to do a backup of any valuable data when performing filesystem operations.

Great solution for a quick creation of quoted directories (for samba shares for example). This even allows for free space monitoring in the directories by Nagios or alike if needed. Thanks a lot folks!

Just wanted to sum things up, I had to dig around a bit to find the right commands.

1. create the mount point
2. create a file full of /dev/zero, large enough to the maximum size you want to reserve for the virtual file-system
3. format this file with an ext3 file-system (you can format a disk space even if it is not a block device, but double check the syntax of every - dangerous - formatting command)
4. mount the newly formatted disk space in the directory you've created as mount point, e.g.
As a result you now have a directory in /path/of/mount/point with a size limitation.

If you wish to add more space to (trim the size of) the directory:
I also found a similar set of tools for reiserfs, couldn't find a resize tool for jfs.

In this solution the space gets eaten away from the host partition(s), use with caution, be sure to save some space for future expansions.

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Hi friends... thanks for the steps to create virtual disks. I'm still new and need your support. I've created the above directory successfully. I wish to know where to configure should i need to mount the directory once the machine start. Please guide me. Thanks...

You add a line to the /etc/fstab file. For example:

Here,

* /var/virtual_disks/directory_with_size_limit.ext3 is the file you created containing the new file system
* /path/of/mount/point is the directory that you want to use and that should have limited size.

So for example if you wanted to limited the size that /var/log can use to 1 GB, then /path/of/mount/point should be replaced with /var/log and /var/virtual_disks/directory_with_size_limit.ext3 should be a 1 GB file.