Category Archives: Operating Systems

Linux : How to create swap area on a live system

This article is about how to create swap space on a live RHEL/CentOS Linux system. However you can still follow that procedure in case you messed up your filesystem and swap is now non-existent (e.g.: swap show 0M). First, use fdisk to edit the partition table and create a partition (this step might be skipped… Read More »

Linux : Installing R1Soft backup agent from YUM repo

Installing R1Soft agent using YUM is pretty straight forward. Simply do the following steps. 1. Edit the R1Soft YUM repo file : /etc/yum.repos.d/r1soft.repo 2. Append the following : [r1soft] name=R1Soft Repository Server baseurl=http://repo.r1soft.com/yum/stable/$basearch/ enabled=1 gpgcheck=0 3. Install the agent : yum install r1soft-cdp-enterprise-agent 4. MISC : You might see the following output message once the… Read More »

Linux : How to change software RAID synchronization speed rate

Here is an easy way to either speed up or slow down the RAID re-synchronization speed rate on Linux. There is many reason why you would do that. Leaving your array rebuilding at full speed might dramatically slow down your server. Set the minimum synchronization speed : echo 102400 > /proc/sys/dev/raid/speed_limit_min Set the maximum synchronization speed… Read More »

Linux : How to disable ICMP echo request

The easiest way of disabling ICMP echo request on Linux is doing it on the kernel level. To disable ICMP immediately on a running system, simply enter the following command : echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all This command will not survive to the next reboot. To make it permanent, edit : vi /etc/sysctl.conf And add :… Read More »

Linux : How to create a dummy file

Here is a quick how to create a dummy file for a specific size under Linux/Unix : dd if=/dev/zero of=<file_name> bs=<size_in_bytes> count=1 So assuming you want to create a file named “100mb.bin” having 100 Mb size : dd if=/dev/zero of=100mb.bin bs=104857600 count=1

OpenVPN : service failed to start due to unresolved dependencies: set([‘bridge’])

If you setup OpenVPN to be in bridge (layer2) mode instead using NAT/routing (layer3) and then restart the server to make the change effective, you probably noticed the following error message on the Status Overview page repeatedly : service failed to start due to unresolved dependencies: set([‘bridge’]) This is because there is no existing bridge… Read More »