sysctl
時動態地修改內核的運行參數
補充說明
sysctl命令 被用於在內核運行時動態地修改內核的運行參數，可用的內核參數在目錄/proc/sys中。它包含一些TCP/ip堆棧和虛擬內存系統的高級選項， 這可以讓有經驗的管理員提高引人注目的系統性能。用sysctl可以讀取設置超過五百個系統變量。
語法
1sysctl(選項)(參數)
選項
1-n：打印值時不打印關鍵字；
2-e：忽略未知關鍵字錯誤；
3-N：僅打印名稱；
4-w：當改變sysctl設置時使用此項；
5-p：從配置文件“/etc/sysctl.conf”加載內核參數設置；
6-a：打印當前所有可用的內核參數變量和值；
7-A：以表格方式打印當前所有可用的內核參數變量和值。
參數
變量=值：設置內核參數對應的變量值。
實例
查看所有可讀變量：
sysctl -a
讀一個指定的變量，例如kern.maxproc：
sysctl kern.maxproc kern.maxproc: 1044
要設置一個指定的變量，直接用variable=value這樣的語法：
1sysctl kern.maxfiles=5000
2kern.maxfiles: 2088 -> 5000
您可以使用sysctl修改系統變量，也可以通過編輯sysctl.conf文件來修改系統變量。sysctl.conf看起來很像rc.conf。它用variable=value的形式來設定值。指定的值在系統進入多用戶模式之後被設定。並不是所有的變量都可以在這個模式下設定。
sysctl變量的設置通常是字符串、數字或者布爾型。（布爾型用 1 來表示'yes'，用 0 來表示'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
編輯此文件：/etc/sysctl.conf
如果該文件爲空，則輸入以下內容，否則請根據情況自己做調整：
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
如果希望屏蔽別人 ping 你的主機，則加入以下代碼：
1# Disable ping requests
2net.ipv4.icmp_echo_ignore_all = 1
編輯完成後，請執行以下命令使變動立即生效：
1/sbin/sysctl -p
2/sbin/sysctl -w net.ipv4.route.flush=1
來源：https://github.com/jaywcjlove/linux-command
最後修改於： Wednesday, January 31, 2024
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