1SYSCTL.D(5)                        sysctl.d                        SYSCTL.D(5)
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NAME

6       sysctl.d - Configure kernel parameters at boot
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SYNOPSIS

9       /etc/sysctl.d/*.conf
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11       /run/sysctl.d/*.conf
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13       /usr/lib/sysctl.d/*.conf
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DESCRIPTION

16       At boot, systemd-sysctl.service(8) reads configuration files from the
17       above directories to configure sysctl(8) kernel parameters.
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CONFIGURATION FORMAT

20       The configuration files contain a list of variable assignments,
21       separated by newlines. Empty lines and lines whose first non-whitespace
22       character is "#" or ";" are ignored.
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24       Note that either "/" or "."  may be used as separators within sysctl
25       variable names. If the first separator is a slash, remaining slashes
26       and dots are left intact. If the first separator is a dot, dots and
27       slashes are interchanged.  "kernel.domainname=foo" and
28       "kernel/domainname=foo" are equivalent and will cause "foo" to be
29       written to /proc/sys/kernel/domainname. Either
30       "net.ipv4.conf.enp3s0/200.forwarding" or
31       "net/ipv4/conf/enp3s0.200/forwarding" may be used to refer to
32       /proc/sys/net/ipv4/conf/enp3s0.200/forwarding.
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34       The settings configured with sysctl.d files will be applied early on
35       boot. The network interface-specific options will also be applied
36       individually for each network interface as it shows up in the system.
37       (More specifically, net.ipv4.conf.*, net.ipv6.conf.*, net.ipv4.neigh.*
38       and net.ipv6.neigh.*).
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40       Many sysctl parameters only become available when certain kernel
41       modules are loaded. Modules are usually loaded on demand, e.g. when
42       certain hardware is plugged in or network brought up. This means that
43       systemd-sysctl.service(8) which runs during early boot will not
44       configure such parameters if they become available after it has run. To
45       set such parameters, it is recommended to add an udev(7) rule to set
46       those parameters when they become available. Alternatively, a slightly
47       simpler and less efficient option is to add the module to modules-
48       load.d(5), causing it to be loaded statically before sysctl settings
49       are applied (see example below).
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CONFIGURATION DIRECTORIES AND PRECEDENCE

52       Configuration files are read from directories in /etc/, /run/, and
53       /usr/lib/, in order of precedence. Each configuration file in these
54       configuration directories shall be named in the style of filename.conf.
55       Files in /etc/ override files with the same name in /run/ and
56       /usr/lib/. Files in /run/ override files with the same name in
57       /usr/lib/.
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59       Packages should install their configuration files in /usr/lib/. Files
60       in /etc/ are reserved for the local administrator, who may use this
61       logic to override the configuration files installed by vendor packages.
62       All configuration files are sorted by their filename in lexicographic
63       order, regardless of which of the directories they reside in. If
64       multiple files specify the same option, the entry in the file with the
65       lexicographically latest name will take precedence. It is recommended
66       to prefix all filenames with a two-digit number and a dash, to simplify
67       the ordering of the files.
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69       If the administrator wants to disable a configuration file supplied by
70       the vendor, the recommended way is to place a symlink to /dev/null in
71       the configuration directory in /etc/, with the same filename as the
72       vendor configuration file.
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EXAMPLES

75       Example 1. Set kernel YP domain name
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77       /etc/sysctl.d/domain-name.conf:
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79           kernel.domainname=example.com
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81       Example 2. Disable packet filter on bridged packets (method one)
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83       /etc/udev/rules.d/99-bridge.rules:
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85           ACTION=="add", SUBSYSTEM=="module", KERNEL=="bridge", RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/net/bridge"
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87       /etc/sysctl.d/bridge.conf:
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89           net.bridge.bridge-nf-call-ip6tables = 0
90           net.bridge.bridge-nf-call-iptables = 0
91           net.bridge.bridge-nf-call-arptables = 0
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93       Example 3. Disable packet filter on bridged packets (method two)
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95       /etc/modules-load.d/bridge.conf:
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97           bridge
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99       /etc/sysctl.d/bridge.conf:
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101           net.bridge.bridge-nf-call-ip6tables = 0
102           net.bridge.bridge-nf-call-iptables = 0
103           net.bridge.bridge-nf-call-arptables = 0
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SEE ALSO

106       systemd(1), systemd-sysctl.service(8), systemd-delta(1), sysctl(8),
107       sysctl.conf(5), modprobe(8)
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111systemd 219                                                        SYSCTL.D(5)
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