Red Hat ENTERPRISE LINUX 3 Reference Manual

Also see for ENTERPRISE LINUX 3 - SECURITY GUIDE: Tuning guide Installation guide Installation guide Installation guide Manual

Contents

74 Chapter 5. The proc File Systemdresses, respectively. A value of 0 allows the kernel to respond, while a value of 1 ignores thepackets.• ip_default_ttl — Sets the default Time To Live (TTL), which limits the number of hops a packetmay make before reaching its destination. Increasing this value can diminish system performance.• ip_forward — Permits interfaces on the system to forward packets to one other. By default, thisfile is set to 0. Setting this file to 1 enables network packet forwarding.• ip_local_port_range — Specifies the range of ports to be used by TCP or UDP when a localport is needed. The first number is the lowest port to be used and the second number specifies thehighest port. Any systems that expect to require more ports than the default 1024 to 4999 shoulduse a range from 32768 to 61000.• tcp_syn_retries — Provides a limit on the number of times the system re-transmits a SYNpacket when attempting to make a connection.• tcp_retries1 — Sets the number of permitted re-transmissions attempting to answer an incom-ing connection. Default of 3.• tcp_retries2 — Sets the number of permitted re-transmissions of TCP packets. Default of 15.The /usr/src/linux-2.4/Documentation/networking/ip-sysctl.txt file contains a com-plete list of files and options available in the /proc/sys/net/ipv4/ directory.A number of other directories exist within the /proc/sys/net/ipv4/ directory and each covers adifferent aspect of the network stack. The /proc/sys/net/ipv4/conf/ directory allows each sys-tem interface to be configured in different ways, including the use of default settings for unconfigureddevices (in the /proc/sys/net/ipv4/conf/default/ subdirectory) and settings that override allspecial configurations (in the /proc/sys/net/ipv4/conf/all/ subdirectory).The /proc/sys/net/ipv4/neigh/ directory contains settings for communicating with a host di-rectly connected to the system (called a network neighbor) and also contains different settings forsystems more than one hop away.Routing over IPV4 also has its own directory, /proc/sys/net/ipv4/route/. Unlike conf/ andneigh/, the /proc/sys/net/ipv4/route/ directory contains specifications that apply to rout-ing with any interfaces on the system. Many of these settings, such as max_size, max_delay, andmin_delay, relate to controlling the size of the routing cache. To clear the routing cache, write anyvalue to the flush file.Additional information about these directories and the possible values for their configuration files canbe found in:/usr/src/linux-2.4/Documentation/filesystems/proc.txt5.3.9.5. /proc/sys/vm/This directory facilitates the configuration of the Linux kernel’s virtual memory (VM) subsystem. Thekernel 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 values related to the bdflush kernel daemon.• kswapd — Sets values for the kernel swap-out daemon, kswapd. This file has three values:512 32 8The first value sets the maximum number of pages that kswapd attempts to free in a single attempt.The larger this number, the more aggressively the kernel can move to free pages. The second valuesets the minimum number of times that kswapd attempts to free a page. The third value sets thenumber of pages kswapd attempts to write in a single attempt. Proper tuning of this final value can