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.default.rp_filter = 2
net.ipv4.conf.*.rp_filter = 2
-net.ipv4.conf.all.rp_filter

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

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

# ping(8) without CAP_NET_ADMIN and CAP_NET_RAW
# The upper limit is set to 2^31-1. Values greater than that get rejected by
# the kernel because of this definition in linux/include/net/ping.h:
#   #define GID_T_MAX (((gid_t)~0U) >> 1)
# That's not so bad because values between 2^31 and 2^32-1 are reserved on
# systemd-based systems anyway: https://systemd.io/UIDS-GIDS.html#summary
-net.ipv4.ping_group_range = 0 2147483647

# 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

# Enable regular file and FIFO protection
fs.protected_regular = 1
fs.protected_fifos = 1