keepalived uses kernel features that have been introduced over time,
but in order to still allow keepalived to be built and run on older
kernel versions it has many checks of what kernel features are available.

Set out below in chronological order are the features that have been added
to Linux that keepalived makes use of if they are available.

If in doubt about features, grep the source tree searching for "Linux". The
source (including configure.ac) attempts to document which kernel version
introduced features that are used conditionally.

At the end of this file is a list of kernel configure options that affect
functionality that keepalived uses.

Distros supported and kernel versions
=====================================
Distro		Oldest ver	Kernel ver	EOL
------		----------	----------	---
Ubuntu		20.04		5.4		April 2025
Debian		12		6.1		10-06-26
RHEL		8		4.18.0		May 2029
CentOS		no support
CentOS Stream	always more recent than oldest RHEL
Fedora		39		6.5		26-11-24
Fedora		40		6.8-6.11	Four weeks after n+2 released
Gentoo		Updated weekly
AlmaLinux	9		5.14		31-05-27
Alpine		3.17		?5.15		22-11-24
Alpine		3.18		6.1		09-05-25
ArchLinux	2024.09.01	6.10.7		Dec 24 - appears to keep last 3 months of installation media, released at beginning of month
Mint		20		5.4		April 2025			https://en.wikipedia.org/wiki/Linux_Mint
openSUSE	15.5		5.14.21		31-12-24			https://en.wikipedia.org/wiki/OpenSUSE
openSUSE	15.6		6.4		31-12-25			https://en.wikipedia.org/wiki/OpenSUSE
SUSE		15 SP5		5.14.21		26-01-25			https://en.wikipedia.org/wiki/SUSE_Linux_Enterprise
SUSE		15 SP6		6.4.0						A service pack is supported for 6 months after release of next service pack (approx annual)
Manjaro		Rolling		4.19.322					https://en.wikipedia.org/wiki/Manjaro and https://manjaristas.org/branch_compare?q=%23kernels
Oracle		7		3.10		31-12-24			https://en.wikipedia.org/wiki/Oracle_Linux
Oracle		8		4.18		31-07-29			https://en.wikipedia.org/wiki/Oracle_Linux

=============================================================================

The oldest kernel version currently supported is Linux 3.10
-----------------------------------------------------------

dnl ----[Check have IPV4_DEVCONF defines - since Linux 3.11]----

./keepalived/check/check_parser.c:#ifdef IP_VS_SVC_F_SCHED1		/* From Linux 3.11 */

Support for open(..., O_TMPFILE,...) added	-- Linux 3.11	/* Backported into RHEL7 linux-3.10 somewhere between 3.10.0-229 and 3.10.0-1160 */

dnl --RTAX_QUICKACK		dnl -- Linux 3.11
dnl --FRA_SUPPRESS_PREFIXLEN	dnl -- Linux 3.12
dnl --FRA_SUPPRESS_IFGROUP	dnl -- Linux 3.12

./keepalived/include/global_data.h:	bool				namespace_with_ipsets;	/* override for namespaces with ipsets on Linux < 3.13 */

./keepalived/vrrp/vrrp_iptables_calls.c:#if defined IP_SET_OP_GET_FNAME		/* Since Linux 3.13 */

./keepalived/vrrp/vrrp_ipset.c:	 * than Linux 3.13, since ipsets didn't understand namespaces prior to that. */

dnl - Introduced in Linux 3.14
AC_CHECK_DECLS([IFA_FLAGS], [], [], [[#include <linux/if_addr.h>]])
AC_CHECK_DECLS([NFT_META_L4PROTO], [], [], [#include <linux/netfilter/nf_tables.h>])

./keepalived/vrrp/vrrp_ipaddress.c:#ifdef IFA_F_MANAGETEMPADDR		/* Linux 3.14 */
./keepalived/vrrp/vrrp_ipaddress.c:#ifdef IFA_F_NOPREFIXROUTE		/* Linux 3.14 */

./keepalived/vrrp/vrrp_ipaddress.c:#ifdef IFA_F_MANAGETEMPADDR		/* Linux 3.14 */
./keepalived/vrrp/vrrp_ipaddress.c:#ifdef IFA_F_NOPREFIXROUTE		/* Linux 3.14 */

dnl ----[ Checks for kernel IFLA_INET6_ADDR_GEN_MODE support ]----
  # Introduced in Linux 3.17

memfd_create - introduced in Linux 3.17 and glibc 2.27		/* Backported into RHEL7 linux-3.10 somewhere between 3.10.0-229 and 3.10.0-1160 */

dnl -- Since Linux 3.18
AC_CHECK_DECLS([IPVS_DEST_ATTR_ADDR_FAMILY], [add_system_opt([IPVS_DEST_ATTR_ADDR_FAMILY])], [], [#include <linux/ip_vs.h>])

dnl -- xt_set_info_match_v4 declared since Linux 3.19

./lib/rttables.c:#ifdef RTPROT_BABEL		/* Since Linux 3.19 */

dnl --RTAX_CC_ALGO		dnl -- Linux 4.0

./keepalived/vrrp/vrrp_ipaddress.c:#ifdef IFA_F_MCAUTOJOIN			/* Linux 4.1 */

dnl -- Since Linux 4.1
IPVS_SVC_ATTR_STATS64,
IPVS_DEST_ATTR_STATS64], [],

dnl --RTA_VIA			dnl -- Linux 4.1
dnl --RTA_NEWDST		dnl -- Linux 4.1
dnl --RTA_PREF			dnl -- Linux 4.1

./keepalived/include/ip_vs.h:/* Prior to Linux 4.2 have to include linux/in.h and linux/in6.h

./keepalived/include/vrrp_iproute.h:#if HAVE_DECL_RTA_ENCAP	/* Since Linux 4.3 */

dnl -- Since Linux 4.3
AC_CHECK_DECLS([
IPVS_DAEMON_ATTR_SYNC_MAXLEN,
IPVS_DAEMON_ATTR_MCAST_GROUP,
IPVS_DAEMON_ATTR_MCAST_GROUP6,
IPVS_DAEMON_ATTR_MCAST_PORT,
IPVS_DAEMON_ATTR_MCAST_TTL], [],

dnl -- Since Linux 4.3
AC_DEFINE([_HAVE_IPVS_SYNCD_ATTRIBUTES_], [ 1 ], [Define to 1 if have IPVS syncd attributes])

dnl --FRA_TUN_ID		dnl -- Linux 4.3
dnl --RTA_ENCAP			dnl -- Linux 4.3

dnl ----[ Checks for kernel IFLA_VRF_... support ]----
  # Introduced in Linux 4.3

MCL_ONFAULT			-- Linux 4.4
dnl --RTEXT_FILTER_SKIP_STATS	dnl -- Linux 4.4
dnl --RTA_EXPIRES		dnl -- Linux 4.5

./keepalived/vrrp/vrrp_iptables.c:/* Linux 4.5 introduced a namespace collision when including
./keepalived/vrrp/vrrp_iptables_calls.c:/* Linux 4.5 introduced a namespace collision when including

# Linux 4.5 to 4.5.4 has <libiptc/libiptc.h> indirectly including <net/if.h>
# and <linux/if.h> which causes a namespace collision.

dnl --FRA_L3MDEV		dnl -- Linux 4.8

dnl --IPVLAN_MODE_L3S		dnl -- Linux 4.9

dnl --FRA_UID_RANGE		dnl -- Linux 4.10

/* CORENAME_MAX_SIZE in kernel source include/linux/binfmts.h defines
 * the maximum string length, * see core_pattern[CORENAME_MAX_SIZE] in
 * fs/coredump.c. Currently (Linux 4.10) defines it to be 128, but the
 * definition is not exposed to user-space. */

dnl --RTA_TTL_PROPAGATE		dnl -- Linux 4.12
IFLA_IPVLAN_FLAGS, IPVLAN_MODE_PRIVATE, IPVLAN_MODE_VEPA - Linux 4.15
dnl --RTAX_FASTOPEN_NO_COOKIE	dnl -- Linux 4.15
dnl --FRA_PROTOCOL		dnl -- Linux 4.17
dnl --FRA_IP_PROTO		dnl -- Linux 4.17
dnl --FRA_SPORT_RANGE		dnl -- Linux 4.17
dnl --FRA_DPORT_RANGE		dnl -- Linux 4.17

./lib/rbtree.c:/* This is updated to Linux v4.18.10 lib/rbtree.c

IPV6_MULTICAST_ALL since Linux v4.20

dnl -- Linux/errqueue.h need sys/time.h before Linux < v5.1

dnl -- Since Linux 5.1
NFT_META_OIFKIND

dnl -- Since Linux 5.2
IPVS_DEST_ATTR_TUN_TYPE

dnl -- Since Linux 5.3
IP_VS_TUNNEL_ENCAP_FLAG_NOCSUM
IP_VS_CONN_F_TUNNEL_TYPE_GRE

??? dnl -- RedHat backported ENCAP_IP and ENCAP_IP6 without MPLS and ILA

dnl -- Since Linux 5.6 and libnftnl 1.1.6, nft 0.9.4
NFTNL_SET_DESC_CONCAT
NFTNL_SET_ELEM_KEY_END

dnl -- Since Linux 5.7
NFT_SET_CONCAT
NFTNL_SET_EXPR also libnftnl 1.1.7, nft 0.9.5

dnl ----[ Is HTTP_GET regex checking wanted? ]----
$PKG_CONFIG --exists libpcre2-8

/* Defined in kernel source file include/linux/sched.h but
 * not currently (Linux v5.10.12) exposed to userspace.
 * Also not currently exposed by glibc (v2.32). */
#define TASK_COMM_LEN 16

=============================================================================

Package versions
================

dnl -- RLIMIT_RTTIME - not defined in musl libc until v1.2.0

libipset v6.38	Used by Debian Buster, EOL ~2022
	 v6.29	Used by Ubuntu 16.04, EOL 04/21

=============================================================================

Kernel configuration requirements
---------------------------------
The following list is probably incomplete, and will be updated as other
options become known.

BPF
EPOLL
SIGNALFD
TIMERFD
SYSCTL
PROC_FS
INET
IP_MULTICAST
IPV6
IP_VS (unless --disable-lvs is specified)
  IP_VS suboptions to match the real_server/virtual_server configuration
NETFILTER_XTABLES - if strict_mode or no_accept.
  NETFILTER_XT options and IP_SET
IP_ADVANCED_ROUTER and various associated options if static/dynamic routes specified
FIB_RULES if static or dynamic rules are specified
NFTABLES
CN_PROC for vrrp track_process
MACVLAN
IPVLAN
