systemd/sysctl.d/50-default.conf

#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

# See sysctl.d(5) and core(5) for documentation.

# To override settings in this file, create a local file in /etc
# (e.g. /etc/sysctl.d/90-override.conf), and put any assignments
# there.

# System Request functionality of the kernel (SYNC)
#
# Use kernel.sysrq = 1 to allow all keys.
# See https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html for a list
# of values and keys.
kernel.sysrq = 16

# Append the PID to the core filename
kernel.core_uses_pid = 1

# Source route verification
net.ipv4.conf.all.rp_filter = 1

# Do not accept source routing
net.ipv4.conf.all.accept_source_route = 0

# Promote secondary addresses when the primary address is removed
net.ipv4.conf.all.promote_secondaries = 1

# Fair Queue CoDel packet scheduler to fight bufferbloat
net.core.default_qdisc = fq_codel

# Enable hard and soft link protection
fs.protected_hardlinks = 1
fs.protected_symlinks = 1