Fix #40: update docs and online help text wrt. caching of kmsg seqno

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

README.md

@@ -132,6 +132,11 @@ sudo make install-strip
 You may want to remove the `--prefix=/usr` option.  Most users prefer
 non-distro binaries in `/usr/local` or `/opt`.
 
+> **Note:** the `--runstatedir` option should point to a filesystem
+>           that is cleaned at reboot.  syslogd relies on this for
+>           its `syslogd.cache` file, which keeps track of the last
+>           read kernel log message from `/dev/kmsg`.
+
 
 Building from GIT
 -----------------

man/syslogd.8

@@ -220,6 +220,13 @@ If
 cannot write to, or read from, this file it will cause repeated kernel
 log messages when restarting
 .Nm .
+.Pp
+.Sy Note:
+.Nm
+relies on this file being removed at system reboot.  The default
+location depends on the system and how
+.Nm
+was configured.
 .It Fl d
 Put
 .Nm
@@ -461,7 +468,10 @@ conventional name for default rules.
 default process ID file
 .It Pa /var/run/syslogd.cache
 cache of last read sequence number from
-.Pa /dev/kmsg
+.Pa /dev/kmsg .
+Please note,
+.Nm
+relies on this file being removed at system reboot.
 .It Pa /dev/log
 name of the
 .Ux

src/syslogd.c

@@ -275,6 +275,7 @@ int usage(int code)
 	       "                                    default: 'syslog', port 514\n"
 	       "\n"
 	       "  -C FILE   File to cache last read kernel seqno, default: %s\n"
+	       "            Note: syslogd relies on this file being removed at system reboot.\n"
 	       "  -d        Enable debug mode, implicitly enables -F to prevent backgrounding\n"
 	       "  -F        Run in foreground, required when monitored by init(1)\n"
 	       "  -f FILE   Alternate .conf file, default: %s\n"