Merge pull request #22968 from keszybz/kernel-4.4

Recommend kernel 4.15 or newer

README

@@ -30,14 +30,21 @@ LICENSE:
         LGPL-2.1-or-later for all code, exceptions noted in LICENSES/README.md
 
 REQUIREMENTS:
-        Linux kernel >= 3.15
-        Linux kernel >= 4.2 for unified cgroup hierarchy support
-        Linux kernel >= 4.10 for cgroup-bpf egress and ingress hooks
-        Linux kernel >= 4.15 for cgroup-bpf device hook
-        Linux kernel >= 4.17 for cgroup-bpf socket address hooks
-        Linux kernel >= 5.3 for bounded-loops in BPF program
-        Linux kernel >= 5.4 for signed Verity images support
-        Linux kernel >= 5.7 for BPF links and the BPF LSM hook
+        Linux kernel ≥ 3.15
+                     ≥ 4.5 for pids controller in cgroup v2
+                     ≥ 4.6 for cgroup namespaces
+                     ≥ 4.9 for RENAME_NOREPLACE support in vfat
+                     ≥ 4.10 for cgroup-bpf egress and ingress hooks
+                     ≥ 4.15 for cgroup-bpf device hook and cpu controller in cgroup v2
+                     ≥ 4.17 for cgroup-bpf socket address hooks
+                     ≥ 5.3 for bounded loops in BPF program
+                     ≥ 5.4 for signed Verity images
+                     ≥ 5.7 for BPF links and the BPF LSM hook
+
+        Kernel versions below 4.15 have significant gaps in functionality and
+        are not recommended for use with this version of systemd. Taint flag
+        'old-kernel' will be set. Systemd will most likely still function, but
+        upstream support and testing are limited.
 
         Kernel Config Options:
           CONFIG_DEVTMPFS
@@ -330,24 +337,41 @@ SYSV INIT.D SCRIPTS:
         Please see src/systemctl/systemd-sysv-install.SKELETON for how this
         needs to look like, and provide an implementation at the marked places.
 
-WARNINGS:
+WARNINGS and TAINT FLAGS:
         systemd will warn during early boot if /usr is not already mounted at
         this point (that means: either located on the same file system as / or
         already mounted in the initrd). While in systemd itself very little
-        will break if /usr is on a separate, late-mounted partition, many of
-        its dependencies very likely will break sooner or later in one form or
+        will break if /usr is on a separate late-mounted partition, many of its
+        dependencies very likely will break sooner or later in one form or
         another. For example, udev rules tend to refer to binaries in /usr,
         binaries that link to libraries in /usr or binaries that refer to data
         files in /usr. Since these breakages are not always directly visible,
-        systemd will warn about this, since this kind of file system setup is
-        not really supported anymore by the basic set of Linux OS components.
-
-        systemd requires that the /run mount point exists. systemd also
-        requires that /var/run is a symlink to /run.
+        systemd will warn about this. Such setups are not really supported by
+        the basic set of Linux OS components. Taint flag 'split-usr' will be
+        set when this condition is detected.
 
         For more information on this issue consult
         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 
+        systemd requires that the /run mount point exists. systemd also
+        requires that /var/run is a symlink to /run. Taint flag 'var-run-bad'
+        will be set when this condition is detected.
+
+        Systemd will also warn when the cgroup support is unavailable in the
+        kernel (taint flag 'cgroups-missing'), the system is using the old
+        cgroup hierarchy (taint flag 'cgroupsv1'), the hardware clock is
+        running in non-UTC mode (taint flag 'local-hwclock'), the kernel
+        overflow UID or GID are not 65534 (taint flags 'overflowuid-not-65534'
+        and 'overflowgid-not-65534'), the UID or GID range assigned to the
+        running systemd instance covers less than 0…65534 (taint flags
+        'short-uid-range' and 'short-gid-range').
+
+        Taint conditions are logged during boot, but may also be checked at any
+        time with:
+
+          busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted
+
+VALGRIND:
         To run systemd under valgrind, compile with meson option
         -Dvalgrind=true and have valgrind development headers installed
         (i.e. valgrind-devel or equivalent). Otherwise, false positives will be

src/basic/def.h

@@ -74,4 +74,4 @@
 /* Path where systemd-oomd listens for varlink connections from user managers to report changes in ManagedOOM settings. */
 #define VARLINK_ADDR_PATH_MANAGED_OOM_USER "/run/systemd/oom/io.system.ManagedOOM"
 
-#define KERNEL_BASELINE_VERSION "3.15"
+#define KERNEL_BASELINE_VERSION "4.15"

src/core/manager.c

@@ -4384,7 +4384,7 @@ char *manager_taint_string(Manager *m) {
 
         buf = new(char, sizeof("split-usr:"
                                "cgroups-missing:"
-                               "cgrousv1:"
+                               "cgroupsv1:"
                                "local-hwclock:"
                                "var-run-bad:"
                                "overflowuid-not-65534:"