[PATCH v2] doc: update kernel version requirement

[Stephen Hemminger <stephen@networkplumber.org>]

The 4.19 kernel version was end of life in December 2024.
Update to 5.4 and also add better description of what "not supported"
means in this case.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
---
v2 - better wording

 doc/guides/linux_gsg/sys_reqs.rst | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/doc/guides/linux_gsg/sys_reqs.rst b/doc/guides/linux_gsg/sys_reqs.rst
index 5a7d9e4a43..ba48b8afc0 100644
--- a/doc/guides/linux_gsg/sys_reqs.rst
+++ b/doc/guides/linux_gsg/sys_reqs.rst
@@ -105,11 +105,20 @@ System Software
 
 **Required:**
 
-*   Kernel version >= 4.19
-
-    The kernel version required is based on the oldest long term stable kernel available
-    at kernel.org when the DPDK version is in development.
-    Compatibility for recent distribution kernels will be kept, notably RHEL/CentOS 7.
+*   Kernel version >= 5.4
+
+    The Linux userspace API is compatible across releases but there are some
+    restrictions. The oldest kernel tested by the DPDK testing infrastructure
+    is the oldest maintained Long Term Stable (LTS) at time of release.
+    The DPDK is likely to still work with older releases but it is not guaranteed.
+    Compatibility for recent distribution kernels will be kept, notably RHEL, and Ubuntu.
+    It may work on older distributions, that are no longer under standard period
+    but this is no longer but this is no longer tested or guaranteed to work.
+    The following are outside the current support window: RHEL 7, SLES 15.5, Ubuntu 20.04
+    and earlier.
+
+    Some drivers and hardware support may require more recent kernels, check the
+    documentation (e.g. :doc:`../nics/index`)
 
     The kernel version in use can be checked using the command::
 
-- 
2.47.2