After looking at several deployments of VMWare, we had one deployment where the company enabled balloon mode which is essentially a way to overcommit memory the hostnode(s) don't have. Let's say you have put your database into memory or use a cached service in Apache or haproxy/nginx. VMWare will start taking some portions of these and at some point it corrupts things and the application running will either crash, malfunction or segfault. Another factor is that OOMwill be........

yum update Loaded plugins: fastestmirror, ovl Determining fastest mirrors Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=container error was 14: curl#6 - "Could not resolve host: mirrorlist.centos.org; Unknown error" One of the configured repositories failed (Unknown), and yum doesn't have enough cached data to continue. At this point the onl........

This was done on a 2900 but applies to all the switches of the same era. Step 1 - Power Cycle and enter recovery mode If you have physical access you can power cycle and hold the mode button down for 15 seconds. After that the SYS light will flash on the switch and you will see the following screenshot. If you don't have physical access (eg. it is a datacenter swich over console only) then power cycle and hit "Ctrl+Pause/B........

It seems that QEMU/KVM's default PS2 mouse and keyboard doesn't work right in most cases. I have especially observed issues using Ctrl+C and Ctrl+V and in Linux you may see repeated key presses in the terminal and you will wonder why you copied something and it's not in the clipboard when you try to paste. The way to temporarily fix it is to press the key that is repeating once(works in Linux but not really in Windows). Sometimes when moving your mouse it will also s........

To disable selinux temporarily and immediately: setenforce 0 To make it permanent edit /etc/selinux/config: vi /etc/selinux/config........

You need to disable vsync like this when running glxgears: vblank_mode=0 glxgears For Nvidia drivers do this: __GL_SYNC_TO_VBLANK=0 glxgears Notice the higher than 59-60 fps results with vblank_mode=0: ATTENTION: default value of option vblank_mode overridden by environment. 7919 frames in 5.0 seconds = 1583.704 FPS 8187 frames in 5.0 seconds = 1637.266 FPS........

In Centos 7 tftpd will not work with selinux. Clients will not be able to connect and this is all you'll see in the log (then nothing more): Sep 18 14:39:15 localhost xinetd[4327]: START: tftp pid=4331 from=192.168.1.65 On the client/computer side you will see this: TFTP. PXE-M0F: Exiting Intel Boot Agent Basically the client is being instantly connected and bloc........

In Firefox I cannot connect to any website, proxy is disabled and outside network access is confirmed, no system or manual proxy was set on this Linux Mint/Ubuntu system. Normally this can be caused by proxy or DNS problems and the weird thing is that traceroute and ping to other IPs worked fine but even connecting to sites by IP was not working. The connection was reset The connection to the server was reset while the page was loading.........

1.) My screensaver would take a long time to disable after hitting a key. 2.) Usually errors like below will follow. 3.) Compiz sometimes uses 100% or high CPU 4.) My window controls will disable (eg. the minimize, maximize and close buttons). It seems like Compiz or appearance/effects disable themselves. Re-enabling Desktop Effects under Appearance temporarily fixes it. 5.) high load in general from things like "Migration" pr........

Within vi if you can't exit /etc/vim/vimrc you can type :syntax off And to turn it back on: :syntax on Many of us have a dark/black background in our terminal/shell making the default syntax unreadable, the solution is to either turn off syntax highlighting with :syntax off or to enable a special option in /etc/vim/vimrc Edit /etc/vim/vimrc The "syntax on" enables the highligh........

Basically you should always be 100% sure that whatever IPyour mail server sends out with has reverse DNS/PTR records. Remember that unless you own your IPs then you won't be able to set your own reverse DNS. Even if you were to create a reverse PTR record on your DNS servers it will be ignored. Reverse DNS is queried to pre-assigned DNS servers of your ISP, so therefore you'll need to contact your ISP/Colo/Hosting provider to do a reverse DNS entry. If you don't have........

Put what you see below into your .htaccessand it will enable errors and notices. (change on to off and 1 to 0 to disable though) php_flag display_startup_errors on php_flag display_errors on php_flag html_errors on Now you'll be able to see errors and notices but this should really only be used for debugging purposes and only temporarily as it can be a security issue since errors can reveal information you wouldn't want hacker........