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Showing posts from February, 2013

Active vs Passive FTP

When a client experiences problems when connecting to your FTP server, one thing you might want to look into is whether you've set your FTP data transfer mode to either active or passive.  Active and passive are two possible modes that an FTP connection can operate on. Taking into consideration the network configurations and security controls in place, you should choose one mode over the other. But before we discuss which mode is best for what scenario, let's first talk about the basics of these two modes, which can best be explained if we start our discussion with the two channels an FTP session normally has. FTP command channel and data channelA typical FTP session operates using two channels: a command (or control) channel and a data channel. As their names imply, the command channel is used for transmitting commands as well as replies to those commands, while the data channel is used for transferring data.  Unless you configure your FTP server differently, you will normally se…

Adding virtual hard disk to Centos VM on Vmware without reboot

So you need to add an additional hard disk to your VM running the Centos/Redhat/Suse family of operating system, but its in production and you can not reboot it.

So how do you go about it?
Well, it is rather easy!
First, open the "edit settings" window, within the VM, either from the console menu, or by right clicking in the VM through the virtual infrastructure client. Add a hard disk and configure it with the size you require. Finally accept the changes and close the window. After a few seconds, the virtual infrastructure client will shown the reconfiguration being complete.
Now logon to the operating system of the VM, as the root user - or use sudo.
You will see that the VM does not see the new disk, i.e. running the command:
fdisk -l
Shows only the existing disks, there is no sign of the new one.
What we need to do is, re-scan the SCSI bus, without rebooting the VM. To do this run the following command:
echo "- - -" >/sys/class/scsi_host/host#/scan