path: root/doc/nft.txt
diff options
authorAnder Juaristi <>2019-08-29 16:09:02 +0200
committerFlorian Westphal <>2019-09-06 16:25:57 +0200
commitf8f32deda31df597614d9f1f64ffb0c0320f4d54 (patch)
tree7e59bf617b39e30936521f000d9202b816472e04 /doc/nft.txt
parentf521033afc41876173e6430cdd45fc07a1b76654 (diff)
meta: Introduce new conditions 'time', 'day' and 'hour'
These keywords introduce new checks for a timestamp, an absolute date (which is converted to a timestamp), an hour in the day (which is converted to the number of seconds since midnight) and a day of week. When converting an ISO date (eg. 2019-06-06 17:00) to a timestamp, we need to substract it the GMT difference in seconds, that is, the value of the 'tm_gmtoff' field in the tm structure. This is because the kernel doesn't know about time zones. And hence the kernel manages different timestamps than those that are advertised in userspace when running, for instance, date +%s. The same conversion needs to be done when converting hours (e.g 17:00) to seconds since midnight as well. The result needs to be computed modulo 86400 in case GMT offset (difference in seconds from UTC) is negative. We also introduce a new command line option (-t, --seconds) to show the actual timestamps when printing the values, rather than the ISO dates, or the hour. Some usage examples: time < "2019-06-06 17:00" drop; time < "2019-06-06 17:20:20" drop; time < 12341234 drop; day "Saturday" drop; day 6 drop; hour >= 17:00 drop; hour >= "17:00:01" drop; hour >= 63000 drop; We need to convert an ISO date to a timestamp without taking into account the time zone offset, since comparison will be done in kernel space and there is no time zone information there. Overwriting TZ is portable, but will cause problems when parsing a ruleset that has 'time' and 'hour' rules. Parsing an 'hour' type must not do time zone conversion, but that will be automatically done if TZ has been overwritten to UTC. Hence, we use timegm() to parse the 'time' type, even though it's not portable. Overwriting TZ seems to be a much worse solution. Finally, be aware that timestamps are converted to nanoseconds when transferring to the kernel (as comparison is done with nanosecond precision), and back to seconds when retrieving them for printing. We swap left and right values in a range to properly handle cross-day hour ranges (e.g. 23:15-03:22). Signed-off-by: Ander Juaristi <> Reviewed-by: Florian Westphal <>
Diffstat (limited to 'doc/nft.txt')
1 files changed, 5 insertions, 1 deletions
diff --git a/doc/nft.txt b/doc/nft.txt
index 3f1074b8..8a49c2fe 100644
--- a/doc/nft.txt
+++ b/doc/nft.txt
@@ -9,7 +9,7 @@ nft - Administration tool of the nftables framework for packet filtering and cla
-*nft* [ *-nNscaeSupyj* ] [ *-I* 'directory' ] [ *-f* 'filename' | *-i* | 'cmd' ...]
+*nft* [ *-nNscaeSupyjt* ] [ *-I* 'directory' ] [ *-f* 'filename' | *-i* | 'cmd' ...]
*nft* *-h*
*nft* *-v*
@@ -93,6 +93,10 @@ For a full summary of options, run *nft --help*.
Read input from an interactive readline CLI. You can use quit to exit, or use the EOF marker,
normally this is CTRL-D.
+ Show time, day and hour values in numeric format.