Thanks! I like the idea. It makes it easy to restore the old behavior globally in case it surprises anybody after update. I would only reword the documentation such that it better reflects what the code actually does. It does not a priory refuse to rotate any log files with multiple hard links, does it? The option only takes an effect if shred or copytruncate is triggered, as I understand it. And we should also refer to these cases as files with multiple hard links. According to stat(2) man page, st_nlink is a number of hard links. So all the files we usually rotate (with st_nlink == 1) have a hard link by definition.

I'll update the wording with regard to file with multiple hard links.

Currently this implementation skips files with multiple hard links by default regardless of other directives (shred, coptruncate).
Are hard-linked log files even a thing? Most files with multiple hard links are binaries or shared libraries, like /usr/bin/uncompress - /usr/bin/gunzip.

My bad. test-0090 actually does not use any of those options. Please embed also the following patch:

--- a/logrotate.c
+++ b/logrotate.c
@@ -400,38 +400,39 @@ static int setSecCtx(int fdSrc, const char *src, char **pPrevCtx)
 static int setSecCtxByName(const char *src, const struct logInfo *log, char **pPrevCtx)
 {
     int hasErrors = 0;
 #ifdef WITH_SELINUX
     int fd;

     if (!selinux_enabled)
         /* pretend success */
         return 0;

     fd = open_logfile(src, log, 0);
     if (fd < 0) {
         message(MESS_ERROR, "error opening %s: %s\n", src, strerror(errno));
         return 1;
     }
     hasErrors = setSecCtx(fd, src, pPrevCtx);
     close(fd);
 #else
     (void) src;
+    (void) log;
     (void) pPrevCtx;
 #endif
     return hasErrors;
 }

 static void restoreSecCtx(char **pPrevCtx)
 {
 #ifdef WITH_SELINUX
     if (!*pPrevCtx)
         /* no security context saved for restoration */
         return;

     /* set default security context to the previously stored one */
     if (selinux_enabled && setfscreatecon_raw(*pPrevCtx) < 0)
         message(MESS_ERROR, "setting default context to %s: %s\n", *pPrevCtx,
                 strerror(errno));

     /* free the memory allocated to save the security context */
     freecon(*pPrevCtx);

... to eliminate the following warning:

logrotate.c: In function 'setSecCtxByName':
logrotate.c:400:67: warning: unused parameter 'log' [-Wunused-parameter]
  400 | static int setSecCtxByName(const char *src, const struct logInfo *log, char **pPrevCtx)
      |                                             ~~~~~~~~~~~~~~~~~~~~~~^~~

... when compiled without SELinux.

Updated the wording and included the fix for the compiler warning without SELinux support (thanks for spotting).

What's your take on the default setting:

• disable completely by default (currently done by this pr)
• disable only when used with copytruncate or shred

Thanks for the update! I think that having allowhardlink disabled by default is fine. If it breaks something, it is easy to restore the old behavior either globally or per log file.