Based upon reviewing the glibc source, the posixrules file is being used
for very specific TZ strings that can be represented as:
[:]stdoffsetdst[offset][,]
If anything follows the above string, even invalid data, posixrules will
not be used. Below is some shell output demonstrating this.
$ TZ="NZST-12:00:00NZDT-13:00:00,ANYTHING" \
strace -eopen date 2>&1 | grep -Ei 'posixrules|jan'
Thu Jan 29 06:53:35 NZDT 2015
$ TZ="NZST-12:00:00NZDT-13:00:00," \
strace -eopen date 2>&1 | grep -Ei 'posixrules|jan'
open("/usr/share/zoneinfo/posixrules", O_RDONLY|O_CLOEXEC) = 3
Thu Jan 29 05:54:58 NZST 2015
Signed-off-by: J William Piggott <elseifthen@xxxxxxx>
---
man3/tzset.3 | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/man3/tzset.3 b/man3/tzset.3
index a9b088d..9cb9d32 100644
--- a/man3/tzset.3
+++ b/man3/tzset.3
@@ -200,6 +200,12 @@ The system timezone file.
The system timezone database directory.
.TP
.B /usr/share/zoneinfo/posixrules
+When a TZ string includes a dst timezone without anything following it,
+then this file is used for the start/end rules.
+It is in the
+.BR tzfile "(5) format."
+By default, the zoneinfo Makefile hard links it to the
+.IR America/New_York " tzfile."
.PP
Above are the current standard file locations, but they are
configurable when glibc is compiled.
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