ifsysctl[-<interface name>] − per network interface sysctl settings


<interface name>


These files are intended to contain sysctl settings, that should be applied when a network interface is created. This are usually interface specific settings, like:

net.ipv6.conf.eth0.use_tempaddr = 2


net.ipv4.conf.eth0.rp_filter = 0

The settings are applied by the /etc/sysconfig/network/scripts/ifup-sysctl script executed via /lib/udev/rules.d/77-network.rules rule (see udev(7)), after the creation and after the rename of the interface name to its persistent name (when applicable), but before the ifup <interface name> -o hotplug may be executed to configure the interface.

The settings are not applied by default when the NetworkManager is active (NETWORKMANAGER=yes), except when the IFSYSCTL_NETWORKMANAGER=yes variable is set in the /etc/sysconfig/network/config file.

Settings from the ifsysctl- file are applied every time an interface has been created.

Settings from the ifsysctl-interface name file are applied when the interface with the corresponding interface name has been created.


The sysctl(8) utility is required to apply the settings. It supports two separator characters for sysctl keywords: a "." in default format and a "/" in the alternate format. Therefore the syntax is basically same to the /etc/sysctl.conf file.

Interface names may contain a ".". In the default sysctl format using a "." as separator, that is any "." in the interface name of the keyword, has to be replaced with a "/". In the alternate sysctl format with "/" as separator, normal interface names can be used.

Optionally, the ifsysctl files may contain also the $INTERFACE and the $SYSCTL_IF variables, that are automatically replaced with the current interface name usable in the alternate format and with the sysctl-quoted interface name for the default format, before the settings are passed to the sysctl utility.

Note also, that settings with variables in the ifsysctl (without the -<interface name> suffix), will be applied for every interface!
Further, files with variables are not compatible to the /etc/sysctl.conf file.


Settings for "eth0" and "eth0.1" interfaces

# using "." as separator:

net.ipv6.conf.eth0.use_tempaddr = 2

net.ipv6.conf.eth0/1.use_tempaddr = 2

# using "/" as separator:

net/ipv6/conf/eth0/use_tempaddr = 2

net/ipv6/conf/eth0.0/use_tempaddr = 2

Settings with variables:

# using "." as separator:

net.ipv6.conf.$SYSCTL_IF.use_tempaddr = 2

# using "/" as separator:

net/ipv6/conf/$INTERFACE/use_tempaddr = 2

To test your ifsysctl-eth0 or ifsysctl file, use:

/etc/sysconfig/network/scripts/ifup-sysctl eth0 -o debug


Please report bugs at <https://bugzilla.novell.com/>


Marius Tomaschewski <mt@suse.de>


ifup(8) ifcfg(5) sysctl(8)

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