I’m guessing that every Linux admin saw this alarming message: “No space left on device”. First thing you are doing is check disk usage of course:

# df -h
 Filesystem              Size  Used Avail Use% Mounted on
 /dev/mapper/vg-lv_root   18G   13G  3.4G  80% /

What is going on? There is a lot of free space! Continue Reading

Sometimes (especially when system works on heavy load) Linux buffers and caches contains a lot of objects. This behaviour is generally highly desirable but let’s take a look at following scenario.

Web server is a victim of a DDoS attack. Most of free RAM is used by caches. DDoS has ended and we quickly need to free some RAM for our main application and database system. Cache will warm-up again but it take some time. We need to initiate cache warm-up now! Continue Reading

Default CentOS repositories contain only most popular packages and doesn’t offer useful packages that are available in other Linux distributions. EPEL repository is an Extra Packages for Enterprise Linux. It provides rebuild of Enterprise Linux packages of Fedora for EL6 and EL7. Generally using that repository is safe and significantly improves system functionality. How to install it? Continue Reading