Linux的sysctl 命令参数详解

Posted 2020-09-28

Linux内核通过/proc虚拟文件系统向用户导出内核信息，用户也可以通过/proc文件系统或通过sysctl命令动态配置内核。比如，如果我们想启动NAT，除了加载模块、配置防火墙外，还需要启动内核转发功能。我们有三种方法：

1. 直接写/proc文件系统 # echo 1 > /proc/sys/net/ipv4/ip_forward

2. 利用sysctl命令 # sysctl -w net.ipv4.ip_forward=1 sysctl -a可以查看内核所有导出的变量

3. 编辑/etc/sysctl.conf 添加如下一行，这样系统每次启动后，该变量的值就是1 net.ipv4.ip_forward = 1

sysctl是procfs软件中的命令，该软件包还提供了w, ps, vmstat, pgrep, pkill, top, slabtop等命令。

sysctl配置与显示在/proc/sys目录中的内核参数．可以用sysctl来设置或重新设置联网功能，如IP转发、IP碎片去除以及源路由检查等。用户只需要编辑/etc/sysctl.conf文件，即可手工或自动执行由sysctl控制的功能。

    命令格式：    sysctl [-n] [-e] -w variable=value    sysctl [-n] [-e] -p <filename> (default /etc/sysctl.conf)    sysctl [-n] [-e] -a    常用参数的意义：    -w   临时改变某个指定参数的值，如         sysctl -w net.ipv4.ip_forward=1    -a   显示所有的系统参数    -p   从指定的文件加载系统参数，如不指定即从/etc/sysctl.conf中加载    如果仅仅是想临时改变某个系统参数的值，可以用两种方法来实现,例如想启用IP路由转发功能：    1) #echo 1 > /proc/sys/net/ipv4/ip_forward    2) #sysctl -w net.ipv4.ip_forward=1    以上两种方法都可能立即开启路由功能，但如果系统重启，或执行了     # service network restart命令，所设置的值即会丢失，如果想永久保留配置，可以修改/etc/sysctl.conf文件将 net.ipv4.ip_forward=0改为net.ipv4.ip_forward=1

 

sysctl是一个允许您改变正在运行中的Linux系统的接口。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。基于这点，sysctl(8) 提供两个功能：读取和修改系统设置。 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： # sysctl kern.maxfiles=5000 kern.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‘)。

sysctl -w kernel.sysrq=0 sysctl -w kernel.core_uses_pid=1 sysctl -w net.ipv4.conf.default.accept_redirects=0 sysctl -w net.ipv4.conf.default.accept_source_route=0 sysctl -w net.ipv4.conf.default.rp_filter=1 sysctl -w net.ipv4.tcp_syncookies=1 sysctl -w net.ipv4.tcp_max_syn_backlog=2048 sysctl -w net.ipv4.tcp_fin_timeout=30 sysctl -w net.ipv4.tcp_synack_retries=2 sysctl -w net.ipv4.tcp_keepalive_time=3600 sysctl -w net.ipv4.tcp_window_scaling=1 sysctl -w net.ipv4.tcp_sack=1

配置sysctl

编辑此文件：

vi /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：

# 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

如果希望屏蔽别人 ping 你的主机，则加入以下代码：

# Disable ping requests net.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：

/sbin/sysctl -p /sbin/sysctl -w net.ipv4.route.flush=1

我们常常在 Linux 的 /proc/sys 目录下,手动设定一些 kernel 的参数或是直接 echo 特定的值给一个 proc下的虚拟档案,俾利某些档案之开启,常见的例如设定开机时自动启动 IP Forwarding: echo “1” > /proc/sys/net/ipv4/ip_forward

其实,在 Linux 我们还可以用 sysctl command 便可以简易的去检视、设定或自动配置 特定的 kernel 设定。我们可以在系统提示符号下输入「sysctl -a」,摘要如后:abi.defhandler_coff = 117440515

dev.raid.speed_limit_max = 100000

net.ipv4.conf.default.send_redirects = 1

net.ipv4.conf.default.secure_redirects = 1

net.ipv4.conf.default.accept_redirects = 1

net.ipv4.conf.default.mc_forwarding = 0

net.ipv4.neigh.lo.delay_first_probe_time = 5

net.ipv4.neigh.lo.base_reachable_time = 30

net.ipv4.icmp_ratelimit = 100

net.ipv4.inet_peer_gc_mintime = 10

net.ipv4.igmp_max_memberships = 20

net.ipv4.ip_no_pmtu_disc = 0

net.core.no_cong_thresh = 20

net.core.netdev_max_backlog = 300

net.core.rmem_default = 65535

net.core.wmem_max = 65535

vm.kswapd = 512 32 8

vm.overcommit_memory = 0

vm.bdflush = 30 64 64 256 500 3000 60 0 0

vm.freepages = 351 702 1053

kernel.sem = 250 32000 32 128

kernel.panic = 0

kernel.domainname = (none)

kernel.hostname = pc02.shinewave.com.tw

kernel.version = #1 Tue Oct 30 20:11:04 EST 2001

kernel.osrelease = 2.4.9-13

kernel.ostype = Linux

fs.dentry-state = 1611 969 45 0 0 0

fs.file-nr = 1121 73 8192

fs.inode-state = 1333 523 0 0 0 0 0