sysctl
时动态地修改内核的运行参数
补充说明
sysctl命令 被用于在内核运行时动态地修改内核的运行参数，可用的内核参数在目录/proc/sys中。它包含一些TCP/ip堆栈和虚拟内存系统的高级选项， 这可以让有经验的管理员提高引人注目的系统性能。用sysctl可以读取设置超过五百个系统变量。
语法
1sysctl(选项)(参数)
选项
1-n：打印值时不打印关键字；
2-e：忽略未知关键字错误；
3-N：仅打印名称；
4-w：当改变sysctl设置时使用此项；
5-p：从配置文件“/etc/sysctl.conf”加载内核参数设置；
6-a：打印当前所有可用的内核参数变量和值；
7-A：以表格方式打印当前所有可用的内核参数变量和值。
参数
变量=值：设置内核参数对应的变量值。
实例
查看所有可读变量：
sysctl -a
读一个指定的变量，例如kern.maxproc：
sysctl kern.maxproc kern.maxproc: 1044
要设置一个指定的变量，直接用variable=value这样的语法：
1sysctl kern.maxfiles=5000
2kern.maxfiles: 2088 -> 5000
您可以使用sysctl修改系统变量，也可以通过编辑sysctl.conf文件来修改系统变量。sysctl.conf看起来很像rc.conf。它用variable=value的形式来设定值。指定的值在系统进入多用户模式之后被设定。并不是所有的变量都可以在这个模式下设定。
sysctl变量的设置通常是字符串、数字或者布尔型。（布尔型用 1 来表示'yes'，用 0 来表示'no'）。
1sysctl -w kernel.sysrq=0
2sysctl -w kernel.core_uses_pid=1
3sysctl -w net.ipv4.conf.default.accept_redirects=0
4sysctl -w net.ipv4.conf.default.accept_source_route=0
5sysctl -w net.ipv4.conf.default.rp_filter=1
6sysctl -w net.ipv4.tcp_syncookies=1
7sysctl -w net.ipv4.tcp_max_syn_backlog=2048
8sysctl -w net.ipv4.tcp_fin_timeout=30
9sysctl -w net.ipv4.tcp_synack_retries=2
10sysctl -w net.ipv4.tcp_keepalive_time=3600
11sysctl -w net.ipv4.tcp_window_scaling=1
12sysctl -w net.ipv4.tcp_sack=1
配置sysctl
编辑此文件：/etc/sysctl.conf
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：
1# Controls source route verification
2# Default should work for all interfaces
3net.ipv4.conf.default.rp_filter = 1
4# net.ipv4.conf.all.rp_filter = 1
5# net.ipv4.conf.lo.rp_filter = 1
6# net.ipv4.conf.eth0.rp_filter = 1
7
8# Disables IP source routing
9# Default should work for all interfaces
10net.ipv4.conf.default.accept_source_route = 0
11# net.ipv4.conf.all.accept_source_route = 0
12# net.ipv4.conf.lo.accept_source_route = 0
13# net.ipv4.conf.eth0.accept_source_route = 0
14
15# Controls the System Request debugging functionality of the kernel
16kernel.sysrq = 0
17
18# Controls whether core dumps will append the PID to the core filename.
19# Useful for debugging multi-threaded applications.
20kernel.core_uses_pid = 1
21
22# Increase maximum amount of memory allocated to shm
23# Only uncomment if needed!
24# kernel.shmmax = 67108864
25
26# Disable ICMP Redirect Acceptance
27# Default should work for all interfaces
28net.ipv4.conf.default.accept_redirects = 0
29# net.ipv4.conf.all.accept_redirects = 0
30# net.ipv4.conf.lo.accept_redirects = 0
31# net.ipv4.conf.eth0.accept_redirects = 0
32
33# enable Log Spoofed Packets, Source Routed Packets, Redirect Packets
34# Default should work for all interfaces
35net.ipv4.conf.default.log_martians = 1
36# net.ipv4.conf.all.log_martians = 1
37# net.ipv4.conf.lo.log_martians = 1
38# net.ipv4.conf.eth0.log_martians = 1
39
40# Decrease the time default value for tcp_fin_timeout connection
41net.ipv4.tcp_fin_timeout = 25
42
43# Decrease the time default value for tcp_keepalive_time connection
44net.ipv4.tcp_keepalive_time = 1200
45
46# Turn on the tcp_window_scaling
47net.ipv4.tcp_window_scaling = 1
48
49# Turn on the tcp_sack
50net.ipv4.tcp_sack = 1
51
52# tcp_fack should be on because of sack
53net.ipv4.tcp_fack = 1
54
55# Turn on the tcp_timestamps
56net.ipv4.tcp_timestamps = 1
57
58# Enable TCP SYN Cookie Protection
59net.ipv4.tcp_syncookies = 1
60
61# Enable ignoring broadcasts request
62net.ipv4.icmp_echo_ignore_broadcasts = 1
63
64# Enable bad error message Protection
65net.ipv4.icmp_ignore_bogus_error_responses = 1
66
67# make more local ports available
68# net.ipv4.ip_local_port_range = 1024 65000
69
70# set TCP Re-Ordering value in kernel to ‘5′
71net.ipv4.tcp_reordering = 5
72
73# Lower syn retry rates
74net.ipv4.tcp_synack_retries = 2
75net.ipv4.tcp_syn_retries = 3
76
77# Set Max SYN Backlog to ‘2048′
78net.ipv4.tcp_max_syn_backlog = 2048
79
80# Various Settings
81net.core.netdev_max_backlog = 1024
82
83# Increase the maximum number of skb-heads to be cached
84net.core.hot_list_length = 256
85
86# Increase the tcp-time-wait buckets pool size
87net.ipv4.tcp_max_tw_buckets = 360000
88
89# This will increase the amount of memory available for socket input/output queues
90net.core.rmem_default = 65535
91net.core.rmem_max = 8388608
92net.ipv4.tcp_rmem = 4096 87380 8388608
93net.core.wmem_default = 65535
94net.core.wmem_max = 8388608
95net.ipv4.tcp_wmem = 4096 65535 8388608
96net.ipv4.tcp_mem = 8388608 8388608 8388608
97net.core.optmem_max = 40960
如果希望屏蔽别人 ping 你的主机，则加入以下代码：
1# Disable ping requests
2net.ipv4.icmp_echo_ignore_all = 1
编辑完成后，请执行以下命令使变动立即生效：
1/sbin/sysctl -p
2/sbin/sysctl -w net.ipv4.route.flush=1
来源：https://github.com/jaywcjlove/linux-command
最后修改于： Wednesday, January 31, 2024
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