Having slow network performances, packet loss and noticed this message in the logs or dmesg output under heavy load on your Linux box? ip_conntrack: table full, dropping packet This is because you reach the limit set for connection tracking. To display the current usage, use the following command : wc -l /proc/net/ip_conntrack In such case,… Read More »
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 »
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 »
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 »
Most of low end motherboard will have IRQ/Call Trace issues on Linux. To resolve this, you might to force irqpoll. To achieve that, edit the grub config : gksudo gedit /boot/grub/menu.lst And then, add “acpi=force irqpoll”: defoptions=quiet splash acpi=force irqpoll Update Grub : sudo update-grub If you are using grub2 : gksudo gedit /etc/default/grub And… Read More »
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 »
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
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 »
You might encountered the following message after creating a bridge interface and try to bring it up on RHEL/CentOS Linux : ifup br0 Device br0 does not seem to be present, delaying initialization. The common error in such case is usually because you mistype the ” TYPE= ” parameter, bridge must start with a… Read More »
You might noticed this error trying to log into a Linux/Unix system through SSH or SFTP : This account is currently not available. The two main possible causes : – The shell does not exist or have been removed; – Typo error when entering the shell path at the user creation. Have a look at… Read More »