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sysctl.md

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sysctl

configure kernel parameters at runtime

References

  • man sysctl

Options

  • -a, --all Display all values currently available.
  • -w, --write Use this option when you want to change a sysctl setting.
  • -p[FILE], --load[=FILE] Load in sysctl settings from the file specified or /etc/sysctl.conf if none given.
    • Specifying as filename means reading data from standard input.
    • Using this option will mean arguments to sysctl are files, which are read in the order they are specified.
    • The file argument may be specified as regular expression.
  • -n, --values Use this option to disable printing of the key name when printing values.
  • -e, --ignore Use this option to ignore errors about unknown keys.
  • -N, --names Use this option to only print the names.
    • It may be useful with shells that have programmable completion.

Config File

e.g.

$ cat /etc/sysctl.conf
# System default settings live in /usr/lib/sysctl.d/00-system.conf.
# To override those settings, enter new settings here, or in an /etc/sysctl.d/<name>.conf file
#
# For more information, see sysctl.conf(5) and sysctl.d(5).
# System default settings live in /usr/lib/sysctl.d/00-system.conf.
# To override those settings, enter new settings here, or in an /etc/sysctl.d/<name>.conf file
#
# For more information, see sysctl.conf(5) and sysctl.d(5).
kernel.panic = 1
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0
net.ipv4.conf.default.arp_ignore = 1
net.ipv4.conf.default.arp_announce = 2
net.ipv4.conf.all.arp_ignore = 1
net.ipv4.conf.all.arp_announce = 2
net.ipv4.ip_no_pmtu_disc = 1

Usage

All

$ sysctl -a
user.cs_path: /usr/bin:/bin:/usr/sbin:/sbin
user.bc_base_max: 99
user.bc_dim_max: 2048
user.bc_scale_max: 99
user.bc_string_max: 1000
user.coll_weights_max: 2
user.expr_nest_max: 32
user.line_max: 2048
user.re_dup_max: 255
user.posix2_version: 200112
……
# TL;DR : Try it yourself

Socket

View

socket 接收缓冲最大值（单位：Byte）

$ sysctl net.core.rmem_max
net.core.rmem_max = 16777216

# or
$ sysctl -a | grep net.core.rmem_max
net.core.rmem_max = 16777216

# or
$ cat /proc/sys/net/core/rmem_max
16777216

Modify

$ sysctl -w net.core.rmem_max=16777216
net.core.rmem_max = 16777216

Ping

Disable

$ sysctl -w net.ipv4.icmp_echo_ignore_all=1

Enable

$ sysctl -w net.ipv4.icmp_echo_ignore_all=0

via config file

Disable / Enable

  • Append content below to /etc/sysctl.conf
    • or modify configuration net.ipv4.icmp_echo_ignore_all in it
# Disable/Enable ping requests
net.ipv4.icmp_echo_ignore_all = 1 # disabled
# or
net.ipv4.icmp_echo_ignore_all = 0 # enabled
  • Bring configs into effect
$ sysctl -p