Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Scaricare il pdf (Pagina 50)

50 Chapter 2. The /proc File System

For a complete list of ﬁles and options available, see /usr/src/linux-

2.4/Documentation/networking/ip-sysctl.txt.

A number of other directories exist within the /proc/sys/net/ipv4/ directory cover speciﬁc top-

ics. The conf directory allows each of the systems interfaces to be conﬁgured in different ways,

including the use of a default settings for unconﬁgured devices (in the default subdirectory) and

settings that override all special conﬁgurations (in the all subdirectory).

In order to control connections between direct neighbors, meaning any other system directly con-

nected to your system, the neigh directory allows special conﬁgurations for each interface. This

would allow you to treat systems differently that you trust more due to their relatively proximity to

your system. At the same time, it also makes it easy to put strict rules in place for systems several

hops away.

Routing over IPV4 also has its own directory, route. Unlike conf and neigh, the route directory

contains speciﬁcations that apply to routing with any interfaces on the system. Many of these settings,

such as max_size, max_delay, and min_delay, relate to controlling the size of the routing cache.

To clear the routing cache, simply write any value to the flush ﬁle.

Additional information about these directories and the possible values for their conﬁguration ﬁles can

be found in /usr/src/linux-2.4/Documentation/filesystems/proc.txt.

2.3.8.5. /proc/sys/vm/

This directory facilitates the conﬁguration of the Linux kernel’s virtual memory (VM) subsystem. The

kernel makes extensive and intelligent use of virtual memory, which is commonly called swap space.

The following ﬁles are commonly found in the /proc/sys/vm/ directory:

• bdflush — Sets various values related to the bdflush kernel daemon.

• buffermem — Allows you to control the percentage amount of total system memory to be used for

buffer memory. Typical output for this ﬁle looks like this:

2 10 60

The ﬁrst and last values set the minimum and maximum percentage of memory to be used as buffer

memory, respectively. The middle value sets the percentage of system memory dedicated to buffer

memory where the memory management subsystem will begin to clear buffer cache more than other

kinds of memory to compensate for a general lack of free memory.

• freepages — Displays various values related to free pages of system memory. This ﬁle looks

similar to this:

512 768 1024

The ﬁrst value shows the minimum number of free pages permitted before the kernel takes over

control of allocating additional memory. The second value gives the number of free pages before

the kernel begins swapping aggressively to preserve performance. The third value is the number of

free pages that the system attempts to keep available at all times.

• kswapd — Sets various values concerned with the kernel swap-out daemon, kswapd. This ﬁle has

three values:

512 32 8

The ﬁrst value sets the maximum number of pages that kswapd will attempt to free in a single

attempt. The larger this number, the more aggressively the kernel can move to free pages. The

second value sets the minimum number of times that kswapd attempts to free a page. The third

value sets the number of pages kswapd attempts to write in a single attempt. Proper tuning of this

ﬁnal value can improve performance on a system using a lot of swap space by telling the kernel to

write pages in large chunks, minimizing the number of disk seeks.

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 50

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