sysctl: do not fail systemd-sysctl.service if /proc/sys is mounted read-only

Let's make missing write access to /proc/sys non-fatal to the sysctl service.

This is a follow-up to 411e869f497c7c7bd0688f1e3500f9043bc56e48 which altered
the condition for running the sysctl service to check for /proc/sys/net being
writable, accepting that /proc/sys might be read-only. In order to ensure the
boot-up stays clean in containers lower the log level for the EROFS errors
generated due to this.

1 files changed, 12 insertions, 5 deletions

diff --git a/src/sysctl/sysctl.c b/src/sysctl/sysctl.c
index fbc1e0eb1a..1363a93830 100644
--- a/src/sysctl/sysctl.c
+++ b/src/sysctl/sysctl.c
@@ -51,11 +51,18 @@ static int apply_all(OrderedHashmap *sysctl_options) {
 
                 k = sysctl_write(property, value);
                 if (k < 0) {
-                        log_full_errno(k == -ENOENT ? LOG_INFO : LOG_WARNING, k,
-                                       "Couldn't write '%s' to '%s', ignoring: %m", value, property);
-
-                        if (r == 0 && k != -ENOENT)
-                                r = k;
+                        /* If the sysctl is not available in the kernel or we are running with reduced privileges and
+                         * cannot write it, then log about the issue at LOG_NOTICE level, and proceed without
+                         * failing. (EROFS is treated as a permission problem here, since that's how container managers
+                         * usually protected their sysctls.) In all other cases log an error and make the tool fail. */
+
+                        if (IN_SET(k, -EPERM, -EACCES, -EROFS, -ENOENT))
+                                log_notice_errno(k, "Couldn't write '%s' to '%s', ignoring: %m", value, property);
+                        else {
+                                log_error_errno(k, "Couldn't write '%s' to '%s': %m", value, property);
+                                if (r == 0)
+                                        r = k;
+                        }
                 }
         }