core: bump net.unix.max_dgram_qlen really early during boot Only that way it actually has an effect on all our sockets, including $NOTIFY_SOCKET.

sysctl.d: bump number of queueable AF_UNIX/SOCK_DGRAM datagrams The default of 16 is pretty low, let's bump this to accomodate for more queued datagrams. This is useful for AF_UNIX/SOCK_DGRAM logging and sd_notify() sockets as this allows queuing more datagrams before things start to block, thus improving parallelization and logging performance.

sysctl: add some hints how to override settings Also a link to decent documentation for sysrq keys. It is surprising hard to find. https://lists.fedoraproject.org/pipermail/devel/2015-February/208412.html

sysctl.d: default to fq_codel, fight bufferbloat Quoting from Jon Corbet's report of Stephen Hemminger's talk at Linux Plumbers Conference 2014 (https://lwn.net/Articles/616241/): [...] So Stephen encouraged everybody to run a command like: sysctl -w net.core.default_qdisc=fq_codel That will cause fq_codel to be used for all future connections [Qdiscs apply to interfaces, not connections. Pointed out by TomH in the article comments. -- mschmidt] (up to the next reboot). Unfortunately, the default queuing discipline cannot be changed, since it will certainly disturb some user's workload somewhere. Let's have the recommended default in systemd. Thanks to Dave Täht for advice and the summary at https://lists.bufferbloat.net/pipermail/cerowrt-devel/2014-October/003701.html

sysctl: always write net.ipv4.conf.all.xyz= in addition to net.ipv4.conf.default.xyz= Otherwise we have a boot-time race, where interfaces that popped up after the sysctl service would get the settings applied, but all others wouldn't.

sysctl.d: enable promote_secondaries by default Without this, secondary addresses would get deleted when the primary one is. This is not the desired behavior when one would like to transition from one address to another in the same subnet (such as when a new IP address is given over DHCP). In networkd, when given a new IP over DHCP we will add it, without explicitly removing the old one first (and hence never have a window without an IP address configured). Assuming the addresses are in the same subnet, that means that the old address is the primary and the new address is the secondary one. Once the old address expires, the kernel will drop it. With the old behavior this means that both addresses would be lost, which is clearly not what we want. With the new behavior, only the old address is lost, and the new one is promoted to primary. Reported by Michael Olbrich <m.olbrich@pengutronix.de>

sysctl: default - add safe sysrq options

sysctl: add 50-default.conf