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--- linux:sysctl [2006/02/10 12:38]
193.77.56.193 created
+++ linux:sysctl [2009/05/25 00:35]
127.0.0.1 external edit
@@ Line 1: / Line 1: @@
 ====== Linux sysctl options ======
+===== Optimized sysctl  =====
+<code conf |f sysctl.conf>
+# the following stops low-level messages on console
+kernel.printk = 4 4 1 7
+# enable /proc/$pid/maps privacy so that memory relocations are not
+# visible to other users.  (Added in kernel 2.6.22.)
+kernel.maps_protect = 1
+# Increase inotify availability
+fs.inotify.max_user_watches = 524288
+# protect bottom 64k of memory from mmap to prevent NULL-dereference
+# attacks against potential future kernel security vulnerabilities.
+# (Added in kernel 2.6.23.)
+vm.mmap_min_addr = 65536
+##############################################################3
+# Functions previously found in netbase
+#
+# Comment the next two lines to disable Spoof protection (reverse-path filter)
+# Turn on Source Address Verification in all interfaces to
+# prevent some spoofing attacks
+net.ipv4.conf.default.rp_filter = 1
+net.ipv4.conf.all.rp_filter = 1
+# Uncomment the next line to enable TCP/IP SYN cookies
+# This disables TCP Window Scaling (http://lkml.org/lkml/2008/2/5/167)
+net.ipv4.tcp_syncookies = 1
+# Uncomment the next line to enable packet forwarding for IPv4
+net.ipv4.ip_forward = 1
+# Uncomment the next line to enable packet forwarding for IPv6
+net.ipv6.ip_forward=0
+###################################################################
+# Additional settings - these settings can improve the network
+# security of the host and prevent against some network attacks
+# including spoofing attacks and man in the middle attacks through
+# redirection. Some network environments, however, require that these
+# settings are disabled so review and enable them as needed.
+#
+# Ignore ICMP broadcasts
+net/ipv4/icmp_echo_ignore_broadcasts = 1
+#
+# Ignore bogus ICMP errors
+net/ipv4/icmp_ignore_bogus_error_responses = 1
+#
+# Do not accept ICMP redirects (prevent MITM attacks)
+net/ipv4/conf/all/accept_redirects = 0
+# _or_
+# Accept ICMP redirects only for gateways listed in our default
+# gateway list (enabled by default)
+net/ipv4/conf/all/secure_redirects = 0
+#
+# Do not send ICMP redirects (we are not a router)
+net/ipv4/conf/all/send_redirects = 1
+# Do not accept IP source route packets (we are not a router)
+net/ipv4/conf/all/accept_source_route = 1
+# tcp/ip tweak - window size
+net.core.wmem_max = 262144
+net.core.rmem_max = 262144
+net.core.wmem_default = 262144
+net.core.rmem_default = 262144
+#
+# Log Martian Packets
+net/ipv4/conf/all/log_martians = 1
+# Always defragment packets
+net/ipv4/ip_always_defrag = 1
+### tnt.aufbix.org tips
+#default#vm/page-cluster = 3
+vm.page-cluster = 6
+#default#net.ipv4.ipfrag_time = 30
+net.ipv4.ipfrag_time = 30
+net.ipv4.tcp_ecn = 1
+net.ipv4.tcp_syncookies = 1
+net.ipv4.tcp_timestamps = 1
+# Linux 2.6 has only 32Mb shared memory
+kernel.shmmax = 67108864
+kernel.random.poolsize = 8192
+# reboot on panic
+kernel.panic = 5
+#net.core.somaxconn=512
+</code>
+**TNT's default sysctl.conf**
+Download {{linux:sysctl.conf}}
+==== Linux as dedicated server ====
+FIXME
+<html><div float=left></html>
+<box 40% round green right|2.6 net/ipv4 options>
+   * [[:linux:sysctl:26netipv4|/proc/net/ipv4]]
+   * [[http://dsd.lbl.gov/TCP-tuning/linux.html|Linux TCP tunning]]
+</box>
+<html></div></html>
+==== Linux as router ====
+  -  The ARP behaviour can be fixed by using **''arp_ignore''**  and **''arp_announce''** on the WAN interface:
+  -   If you have multiple interfaces on the same subnet, you may also want to enable **''arp_filter''**
+      *  This prevents the ARP entry for an interface to fluctuate between two or more MAC addresses. However, you need to use source routing to make this work correctly. From the //Documentation/networking/ip-sysctl-2.6.txt//  file in the kernel source
+  -  The ARP cache timeout on Linux-based routers should be changed from the default, especially if you have a large number of peers. This parameter can be tuned by setting the appropriate procfs variable through the sysctl interface
+       * **change it so it's between 2 and 6 hours, and not 30 min as default.**
+  -  You may need to turn off the //Reverse Path Filter// (''**rp_filter**'') functionality on a Linux-based router to allow asymmetric routing, particularly on your WAN interface.
+''**/etc/sysctl.conf**''
+   # These settings should be duplicated for all interfaces that are
+   # on a peering LAN.
+   ### Typical stuff you really want on a router
+   # Fix the "promiscuous ARP" thing...
+   net/ipv4/conf/ifname/arp_ignore=1
+   net/ipv4/conf/ifname/arp_announce=1
+   # Turn off RP filtering to allow asymmetric routing:
+   net/ipv4/conf/ifname/rp_filter=0
+   # Multiple (non-aggregated) interfaces on the same peering LAN.
+   # READ THE MANUAL FIRST!
+   #net/ipv4/conf/ifname/arp_filter=1
+   ### Keep the AMS-IX ARP Police happy. :-)
+   net/ipv4/neigh/ifname/base_reachable_time=14400
+   net/ipv6/neigh/ifname/base_reachable_time=14400
+===== Misc add-on options on good to know bases  =====
 ==== Reboot on kernel panic ====
@@ Line 7: / Line 160: @@
 |  0  | won't reboot on kernel panic |
 |  n  | number of seconds to wait before reboot |
+==== Linux 2.6 has only 32Mb shared memory ====
+  kernel.shmmax = 67108864
+==== ip_conntrack: maximum limit of XXX entries exceeded ====
+If you notice the following message in syslog, it looks like the conntrack database doesn't have enough entries for your environment. Connection tracking by default handles up to a certain number of simultaneous connections. This number is dependent on you system's maximum memory size (at 64MB: 4096, 128MB: 8192, ...).
+You can easily increase the number of maximal tracked connections, but be **aware that each tracked connection eats about 350 bytes of non-swappable kernel memory!** ''Your kernel will crash for sure, althouh routing/forwarding should still be "working".''
+To increase this limit to e.g. 8192, type:
+   echo "8192" > /proc/sys/net/ipv4/ip_conntrack_max
+To optimize performance, please also raise the number of hash buckets by using the hashsize module loadtime parameter of the ip_conntrack.o module. Please note that due to the nature of the current hashing algorithm, an even hash bucket count (and esp. values of the power of two) are a bad choice.
+Example (with 1023 buckets):
+   modprobe ip_conntrack hashsize=1023
+[[http://www.netfilter.org/documentation/FAQ/netfilter-faq.html#toc3.7]]
+===== GrSecurity options =====
+{{page>linux:grsec#sysctl}}
+About GrSecurity see [[linux:grsec#sysctl|this page]]
-==== TNT's default sysctl.conf ====
-Download here