Managing Resources
55
Managing System Parameters
The resources a Virtual Private Server may allocate are defined by the system resource control
parameters. These parameters can be subdivided into the following categories: primary,
secondary, and auxiliary parameters. The primary parameters are the start point for creating a
Virtual Private Server configuration from scratch. The secondary parameters are dependent on
the primary ones and are calculated from them according to a set of constraints. The auxiliary
parameters help improve fault isolation among applications in one and the same Virtual Private
Server and the way applications handle errors and consume resources. They also help enforce
administrative policies on Virtual Private Servers by limiting the resources required by an
application and preventing the application to run in the Virtual Private Server.
Listed below are all the system resource control parameters. The parameters starting with "num"
are measured in integers. The parameters ending in "buf" or "size" are measured in bytes. The
parameters containing "pages" in their names are measured in 4096-byte pages (IA32
architecture). The
File
column indicates that all the system parameters are defined in the
corresponding VPS configuration files (V).
Primary parameters
Parameter
Description
File
avnumproc
The average number of processes and threads.
V
numproc
The maximal number of processes and threads the VPS may create.
V
numtcpsock
The number of TCP sockets (PF_INET family, SOCK_STREAM
type). This parameter limits the number of TCP connections and, thus,
the number of clients the server application can handle in parallel.
V
numothersock
The number of sockets other than TCP ones. Local (UNIX-domain)
sockets are used for communications inside the system. UDP sockets
are used, for example, for Domain Name Service (DNS) queries. UDP
and other sockets may also be used in some very specialized
applications (SNMP agents and others).
V
vmguarpages
The memory allocation guarantee, in pages (one page is 4 Kb). VPS
applications are guaranteed to be able to allocate additional memory so
long as the amount of memory accounted as
privvmpages
(see the
auxiliary parameters) does not exceed the configured barrier of the
vmguarpages
parameter. Above the barrier, additional memory
allocation is not guaranteed and may fail in case of overall memory
shortage.
V
Secondary parameters
Parameter
Description
File
kmemsize
The size of unswappable kernel memory allocated for the internal
kernel structures for the processes of a particular VPS.
V
tcpsndbuf
The total size of send buffers for TCP sockets, i.e. the amount of
kernel memory allocated for the data sent from an application to a TCP
socket, but not acknowledged by the remote side yet.
V