On Mon, Nov 02, 2026 at 03:01:00PM +0000, Stuart Henderson wrote:
> > +static int
> > +localtz_is_utc(void)
> > +{
> > +	time_t now;
> > +	struct tm *local;
> > +
> > +	now = time(NULL);
> > +	local = localtime(&now);
> > +	return local->tm_gmtoff == 0;
> > +}
> 
> that messes up the formatting if run across a DST change in +0000/+0100
> timezones (Europe/Dublin, Europe/Jersey, Europe/London, etc).

Gaaah... why is it so hard to figure out if the system timezone is Etc/UTC?

Perhaps it is better to just start with using ISO8601, and possibly
later on use 'Z' instead of '+0000' if the systemzone is Etc/UTC.

How about

Index: ts.1
===================================================================
RCS file: /cvs/src/usr.bin/ts/ts.1,v
diff -u -p -r1.8 ts.1
--- ts.1	3 Jul 2022 16:55:39 -0000	1.8
+++ ts.1	2 Nov 2026 15:34:18 -0000
@@ -52,7 +52,7 @@ specifications described in the
 .Xr strftime 3
 manual page.
 The default format is
-.Qq %b %d %H:%M:%S ;
+.Qq %Y-%m-%dT%H:%M:%S%z ;
 or
 .Qq %H:%M:%S
 if one of the
@@ -79,9 +79,9 @@ and
 .Qq 4:20:00.00001 .
 .Sh EXAMPLES
 .Bd -literal -offset indent
-$ (echo foo; sleep 2; echo bar) | ts
-Jun 28 12:13:38 foo
-Jun 28 12:13:40 bar
+$ (echo foo; sleep 2; echo bar) | TZ=Etc/UTC ts
+2026-11-02T15:32:53+0000 foo
+2026-11-02T15:32:55+0000 bar
 
 $ ls | ts -i %.S
 00.000452 CVS
Index: ts.c
===================================================================
RCS file: /cvs/src/usr.bin/ts/ts.c,v
diff -u -p -r1.11 ts.c
--- ts.c	11 Oct 2022 07:36:27 -0000	1.11
+++ ts.c	2 Nov 2026 15:34:18 -0000
@@ -34,7 +34,7 @@ struct usec {
 	char *pos;
 };
 
-static char		*format = "%b %d %H:%M:%S";
+static char		*format = "%Y-%m-%dT%H:%M:%S%z";
 static char		*buf;
 static char		*outbuf;
 static size_t		 bufsize;