On Fri, 19-Dec-2025 at 20:37:41 +0000, Jamie Landeg-Jones wrote:
> void <[email protected]> wrote:
>
> >...
> > and so dmsg has things like
> >
> > [1353919] swp_pager_getswapspace(32): failed
> >
> > the [1353919] I guess being the timestamp.
> >
> > ...
> >
> Yes! You can get the value from sysctl kern.boottime.
>
> Here is a small program I wrote a while back, just call it
> as a dmesg substitute.
> ...
> Cheers, Jamie
>
> #!/bin/sh -efu
> set -efu
>
> boottime="$(/sbin/sysctl -n kern.boottime | /usr/local/bin/gawk '{printf
> "%d", gensub ("^.* sec = ([1-9][0-9]*), .*$", "\\1", 1)}')"
>
> [ -z "$(printf '%s' "$boottime" | /usr/bin/egrep '^0$|^[1-9][0-9]*$')" ] && {
> printf 'Invalid boottime retrieved.\n' >& 2; exit 1; }
>
> /sbin/dmesg "$@" | /usr/local/bin/gawk -v boottime="$boottime" '
>
> {
> uptime = gensub ("^\\[([1-9][0-9]*)\\] .*$", "\\1", 1)
> if (uptime == $0) realtime = "??? ?? ??:??;??"
> else realtime = strftime ("%b %d %T", uptime + boottime)
>
> print realtime " " $0
> }'
FWIW, this is a patch for dmesg(1) I use. You can enable timestamp
conversion using -t and optionally specify a different output format
using -f "fmt".
If interested for inclusion in base, I could try to re-format it
and come up with a manpage diff...
--- sbin/dmesg/dmesg.c 2023-12-27 17:49:57.000000000 +0100
+++ sbin/dmesg/dmesg.c 2026-01-22 09:20:28.987020000 +0100
@@ -60,6 +60,7 @@
#include <unistd.h>
#include <vis.h>
#include <sys/syslog.h>
+#include <time.h>
static struct nlist nl[] = {
#define X_MSGBUF 0
@@ -76,18 +77,23 @@
main(int argc, char *argv[])
{
struct msgbuf *bufp, cur;
+ struct timeval boottime;
+ char timebuf[64];
char *bp, *ep, *memf, *nextp, *nlistf, *p, *q, *visbp;
+ const char *timefmt = "%d %b %T";
kvm_t *kd;
+ time_t time;
size_t buflen, bufpos;
long pri;
- int ch, clear;
+ int ch, clear, timeconv;
bool all;
all = false;
clear = false;
+ timeconv = false;
(void) setlocale(LC_CTYPE, "");
memf = nlistf = NULL;
- while ((ch = getopt(argc, argv, "acM:N:")) != -1)
+ while ((ch = getopt(argc, argv, "actf:M:N:")) != -1)
switch(ch) {
case 'a':
all = true;
@@ -95,6 +101,12 @@
case 'c':
clear = true;
break;
+ case 't':
+ timeconv = true;
+ break;
+ case 'f':
+ timefmt = optarg;
+ break;
case 'M':
memf = optarg;
break;
@@ -109,6 +121,13 @@
if (argc != 0)
usage();
+ if( timeconv ) {
+ int mib[6] = { CTL_KERN, KERN_BOOTTIME };
+ size_t l = sizeof boottime;
+ if (sysctl(mib, 2, &boottime, &l, 0, 0) < 0)
+ err(1, "sysctl kern.boottime");
+ }
+
if (memf == NULL) {
/*
* Running kernel. Use sysctl. This gives an unwrapped buffer
@@ -200,7 +219,22 @@
}
(void)strvisx(visbp, p, nextp - p, 0);
- (void)printf("%s", visbp);
+ bufpos = strspn( visbp+1, "0123456789" ) + 1;
+ if( timeconv != true
+ || bufpos < 2
+ || visbp[0] != '['
+ || visbp[bufpos] != ']'
+ || visbp[bufpos+1] != ' ' ) {
+ (void)printf("%s", visbp);
+ continue;
+ }
+
+ visbp[bufpos] = '\0';
+ time = boottime.tv_sec + strtoull( visbp+1, NULL, 10 );
+ if( strftime( timebuf, sizeof timebuf, timefmt, localtime(
&time ) ) != 0 )
+ (void)printf( "[%s]%s", timebuf, visbp + bufpos + 1 );
+ else
+ (void)printf("%s", visbp);
}
exit(0);
}
@@ -208,6 +242,6 @@
void
usage(void)
{
- fprintf(stderr, "usage: dmesg [-ac] [-M core [-N system]]\n");
+ fprintf(stderr, "usage: dmesg [-ac] [-t [-f output_fmt]] [-M core [-N
system]]\n");
exit(1);
}
-Andre
