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How to Check XEN/OpenVZ VPS Memory/RAM Usage with SSH

To check used and unused memory and swap space on XEN or OpenVZ VPS is easy. The free command provides information about memory usage on VPS running Linux or another Unix-like operating system.

The basic syntax of free is

free [options]

Free accepts no arguments (i.e., input data) and is commonly used without any options.
Below is the example of free command on a XEN VPS

             total       used       free     shared    buffers     cached
Mem:       1015876     969688      46188          0      58876     679356
-/+ buffers/cache:     231456     784420
Swap:      1048568        912    1047656

Another example of free command on a OpenVZ VPS

             total       used       free     shared    buffers     cached
Mem:       1048576     223836     824740          0          0      78060
-/+ buffers/cache:     145776     902800
Swap:      1310720       8752    1301968

Some people might question Xen memory usage. Is XEN VPS used up most of the memory? No worry, your ram is fine! XEN VPS is more like a real dedicated Linux server. Linux system will borrow unused memory for disk caching. This makes it looks like you are low on memory.

Xen in their work makes a connection between the environment of OS and the server hardware. OpenVZ creates a virtual server as a layer that runs on another operating system.The model of memory allocation between XEN VPS and OpenVZ is different. Xen provides better isolation and dedicated memory, OpenVZ uses a shared kernel approach so resources are more shared.

To put it in simple, for OpenVZ VPS, the most important information for free memory is the first row's free value


For XEN VPS, the free memory available is the second row's free value, - buffers/cache is the "used", + buffers/cache is "free"


Several options are available to change the unit of display for free from its default kilobytes, including -b for bytes, -m for megabytes and -g for gigabytes. Of these, -m is usually the most useful. Thus, for example, to show all of the data in megabytes, the following would be used:

free -m

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