人们常说，服务器的负载能力，很大程度上取决于系统管理员的配置和优化能力。这个是对的，相同的硬件、不同的软件配置，会造成截然不同的效果。下面我将给大家介绍一下如何优化 sysctrl, Apache 以及 MySQL 。请注意，所有配置均为取决于个人，请根据自己的实际情况做调整。
配置Sysctl
编辑此文件：
[code]nano -w /etc/sysctl.conf[/code]
如果该文件为空，则输入以下内容，否则请根据情况自己做调整：
[code]# Controls source route verification
# Default should work for all interfaces
net.ipv4.conf.default.rp_filter = 1
# net.ipv4.conf.all.rp_filter = 1
# net.ipv4.conf.lo.rp_filter = 1
# net.ipv4.conf.eth0.rp_filter = 1
# Disables IP source routing
# Default should work for all interfaces
net.ipv4.conf.default.accept_source_route = 0
# net.ipv4.conf.all.accept_source_route = 0
# net.ipv4.conf.lo.accept_source_route = 0
# net.ipv4.conf.eth0.accept_source_route = 0
# Controls the System Request debugging functionality of the kernel
kernel.sysrq = 0
# Controls whether core dumps will append the PID to the core filename.
# Useful for debugging multi-threaded applications.
kernel.core_uses_pid = 1
# Increase maximum amount of memory allocated to shm
# Only uncomment if needed!
# kernel.shmmax = 67108864
# Disable ICMP Redirect Acceptance
# Default should work for all interfaces
net.ipv4.conf.default.accept_redirects = 0
# net.ipv4.conf.all.accept_redirects = 0
# net.ipv4.conf.lo.accept_redirects = 0
# net.ipv4.conf.eth0.accept_redirects = 0
# Enable Log Spoofed Packets, Source Routed Packets, Redirect Packets
# Default should work for all interfaces
net.ipv4.conf.default.log_martians = 1
# net.ipv4.conf.all.log_martians = 1
# net.ipv4.conf.lo.log_martians = 1
# net.ipv4.conf.eth0.log_martians = 1
# Decrease the time default value for tcp_fin_timeout connection
net.ipv4.tcp_fin_timeout = 25
# Decrease the time default value for tcp_keepalive_time connection
net.ipv4.tcp_keepalive_time = 1200
# Turn on the tcp_window_scaling
net.ipv4.tcp_window_scaling = 1
# Turn on the tcp_sack
net.ipv4.tcp_sack = 1
# tcp_fack should be on because of sack
net.ipv4.tcp_fack = 1
# Turn on the tcp_timestamps
net.ipv4.tcp_timestamps = 1
# Enable TCP SYN Cookie Protection
net.ipv4.tcp_syncookies = 1
# Enable ignoring broadcasts request
net.ipv4.icmp_echo_ignore_broadcasts = 1
# Enable bad error message Protection
net.ipv4.icmp_ignore_bogus_error_responses = 1
# Make more local ports available
# net.ipv4.ip_local_port_range = 1024 65000
# Set TCP Re-Ordering value in kernel to ‘5′
net.ipv4.tcp_reordering = 5
# Lower syn retry rates
net.ipv4.tcp_synack_retries = 2
net.ipv4.tcp_syn_retries = 3
# Set Max SYN Backlog to ‘2048′
net.ipv4.tcp_max_syn_backlog = 2048
# Various Settings
net.core.netdev_max_backlog = 1024
# Increase the maximum number of skb-heads to be cached
net.core.hot_list_length = 256
# Increase the tcp-time-wait buckets pool size
net.ipv4.tcp_max_tw_buckets = 360000
# This will increase the amount of memory available for socket input/output queues
net.core.rmem_default = 65535
net.core.rmem_max = 8388608
net.ipv4.tcp_rmem = 4096 87380 8388608
net.core.wmem_default = 65535
net.core.wmem_max = 8388608
net.ipv4.tcp_wmem = 4096 65535 8388608
net.ipv4.tcp_mem = 8388608 8388608 8388608
net.core.optmem_max = 40960[/code]
如果希望屏蔽别人 ping 你的主机，则加入以下代码：
[code]# Disable ping requests
net.ipv4.icmp_echo_ignore_all = 1[/code]
编辑完成后，请执行以下命令使变动立即生效：
[code]/sbin/sysctl -p
/sbin/sysctl -w net.ipv4.route.flush=1[/code]
MySQL优化
编辑MySQL的配置文件：
[code]nano /etc/my.cnf[/code]
输入以下内容：
[code][mysqld]
connect_timeout=15
interactive_timeout=100
join_buffer_size=1M
key_buffer=128M
max_allowed_packet=16M
max_connections=500
max_connect_errors=10
myisam_sort_buffer_size=64M
read_buffer_size=1M
read_rnd_buffer_size=768K
sort_buffer_size=1M
table_cache=1024
thread_cache_size=100
thread_concurrency=4
wait_timeout=300
query_cache_size=32M
query_cache_limit=1M
query_cache_type=1
skip-innodb[/code]
请注意，以上配置适用于512M~1024M内存，如内存更大的话请自行做调整。给项目增加内存会加快速度，但是使用过多的内存而导致启用swap的话，会极大的导致系统效率下降。其中 thread_concurrency 这项配置，单CPU的话请设置为2，双CPU的话请设置为4。
Apache优化
以下优化适用于 Apache 1.3 系列，如果你用的是 2.0 系列的话，请自行做调整和判断。
确认 Apache 的配置文件位置并开始编辑：
[code]locate httpd.conf
nano -w /path/to/httpd.conf[/code]
httpd.conf的文件有许多内容，笔者就拿出需要做优化的：
[code]KeepAlive On
MaxKeepAliveRequests 1000
KeepAliveTimeout 3
MinSpareServers 8
MaxSpareServers 13
MaxRequestsPerChild 50[/code]
将 KeepAliveTimeout 设定到较小的数字将有助于减少服务器上的无用等待链接，一定程度上能增加服务器负载。
另外，下面这条不算优化，但是是Apache安全相关：
[code]ServerSignature Off
ServerTokens ProductOnly[/code]
将 ServerSignature 关闭，并增加 ServerTokens ProductOnly 可以使常人无法检测到Apache的实际版本号，有助于Apache的安全。
以上所做的这些优化在某种程度上会增强服务器的负载性能。但请注意，最佳的配置是实践出来的。
