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
从上述的语法我们大概可看出 sysctl 的表示法乃把目录结构的「/」以「.」表示,一层一层的连结下去。当然以echo 特定的值给一个 proc下的虚拟档案也是可以用 sysctl加以表示,例如:
#sysctl –w net.ipv4.ip_forward =”1”
或是直接在 /etc/sysctl.conf 增删修改特定档案的 0,1值亦可:
# Enables packet forwarding
net.ipv4.ip_forward = 1
# Enables source route verification
net.ipv4.conf.default.rp_filter = 1
# Disables the magic-sysrq key
kernel.sysrq = 0
当然如果考虑 reboot 后仍有效, 直接在 /etc/sysctl.conf 增删修改特定档案的 0,1值才可使之保留设定(以RedHat 为例,每次开机系统启动后, init 会执行 /etc/rc.d/rc.sysinit,便会使用 /etc/sysctl.conf 的预设值去执行 sysctl)。
相关参考档案:
/sbin/sysctl
/etc/sysctl.conf
sysctl 及sysctl.conf manpage
/usr/src/linux-x.y.z/Documentation/sysctl/*
/usr/share/doc/kernel-doc-x.y.z/sysctl/* (RedHat)
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