GLUG

Continuation of the theme from my previous post  - to attempt to highlight useful OSS apps that are maybe not so familiar, but are extremely useful. The next application I would like to talk about is sshfs.

Ever need to mount a filesystem over the network, but for whatever reason, you cannot use nfs or smbfs? Sshfs allows you to mount an accessible directory from a remote machine using only ssh. Another benefit is that all communication to that mount is encrypted by ssh - making it a secure mount as well.

Install sshfs. It should be apparent to readers of this blog how to install an app on their favourite distro, so I will not go into details on the installation.

To mount a directory using sshfs use the following command - in my case I do it as root :

# sshfs scott@192.168.0.7:/mnt/testraid5 /home/scott/thumpa -o allow_other -o uid=500

# mount
/dev/mapper/Vol1-root on / type ext3 (rw,relatime)
none on /proc type proc (rw)
/dev/md1 on /boot type ext3 (rw,relatime)
/dev/mapper/Vol2-1 on /home type ext3 (rw,relatime)
/dev/mapper/Vol1-usr on /usr type ext3 (rw,relatime)
/dev/mapper/Vol1-var on /var type ext3 (rw,relatime)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
none on /sys/fs/fuse/connections type fusectl (rw)
scott@192.168.0.7:/mnt/testraid5 on /home/scott/thumpa type fuse.sshfs (rw,nosuid,nodev,max_read=65536,allow_other)

If you use key authentication, ensure that you su to root WITHOUT 'su -' and just 'su'

Thought I would start a series of posts like this to highlight some of the great apps that are maybe not too familiar with the average linux/OSS user. I will start with the synergy application.

Synergy is a command line tool that is used to share one keyboard and mouse across a multitude of machines. The sourceforge page can be found at http://synergy2.sourceforge.net/ It has good documentation and FAQs and is very straight forward to follow.

Synergy is available for most operating systems and works in a client server mode where the server has the physical mouse and keyboard and runs a daemon on port 24800.

The clients connect to the server and can then share that keyboard and mouse. The configuration is very straight forward and is configured by the principal of relative positions to each other i.e.

client is left of server; server is right of client

A great app that is very underated in my opinion. Those who know it and use it regularly will be wondering how people who do not survive without it!

The logical volume manager. Inconspicuous, unassuming but could quite honestly be one of the most integral parts of the linux OS. For those who have not really cared or taken much notice about the finer points of LVM, then this blog post may change your mind.

LVM can be used in a multitude of ways some of them being -

• Provide data protection by way or mirroring volumes
• Provide increased I/O performance by way of striping across volumes
• Ability to resize and reshape volumes on the fly
• Provide backup utilities using snapshots

These are a just a few of the benefits of understanding more about LVM. My experience in particular was to create GPT partitions on 22 SAN attached LUNS without losing my data. My LVM metadata was written directly on the LUN rather than a partition on the LUN so I had the problem of now trying to create the partition which required the first 34 sectors which would overwrite the LVM metadata which was situated at the first 4 sectors. Dilemma.

Each LUN was in it's own volume group and the logical volume that the file system sits on, was within that volume group. So the solution here was to add another physical volume to the volume group with the vgextend command and remove the existing one so I could then do what I want with it. It can immediately be seen how this may be benificial to other problems. For example if the problem was to replace the existing disks with bigger or faster disks, then the same methodology would also be relevant.

I now have 2 physical volumes in my volume group and using the pvmove command I could move the extents off the volume I so wish. One piece of advice here though is that this can be extremely time consuming, so it is a good idea to reduce the file system to not much bigger than what is absolutely necessary and in turn reduce the size of the logical volume.

Once the pvmove command is complete, the vgreduce -a command can be executed to remove the physical volume from the volume group. If the physical volume is still in use, vgreduce will inform you that ir is so and therefore will not trash your VG. It is always a good idea anyway to use the -t option (test).

Now that all the extents have been moved to the replacement disk, the old disk can be removed with the pvremove command and then what ever is required to be done with the disk/s can be done. To put back all that needs to be done is the reverse of the process - pvcreate, vgextend to add the disk again and then pvmove the subsitute disk.

Don't forget to lvresize and resize2fs back to the way it was after your done!

Another handy little tip is to keep copies of your /etc/lvm/archive and /etc/lvm/backup directories. Should for any reason you lose the lvm metadata on your physical volumes, then your going to need the above to piece everything back together.

Well folks, if you're a regular visitor to our site, you'll notice things are slightly different. Yep, we have a new look and feel! And that's not all that's new...

Under the hood, we're now running Drupal 6.x, the latest stable release. It provides a few new bits and bobs that will help us to manage the site, and you to use the site.

We've also recently gotten the wiki up and running. Please don't be scared to contribute content, a wiki is only successful when everyone lends a hand.

Have fun!