journalctl: show friendly info when using -b on runtime journal only

Make it clear that specifing boot when there is actually only one has no
effect. This cosmetic patch improves user experience a bit.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/journal/journalctl.c b/src/journal/journalctl.c
index db11421e7a..69a2013df8 100644
--- a/src/journal/journalctl.c
+++ b/src/journal/journalctl.c
@@ -2091,6 +2091,13 @@ int main(int argc, char *argv[]) {
                 assert_not_reached("Unknown action");
         }
 
+        if (arg_boot_offset != 0 &&
+            sd_journal_has_runtime_files(j) > 0 &&
+            sd_journal_has_persistent_files(j) == 0) {
+                log_info("Specifying boot ID has no effect, no persistent journal was found");
+                r = 0;
+                goto finish;
+        }
         /* add_boot() must be called first!
          * It may need to seek the journal to find parent boot IDs. */
         r = add_boot(j);