doc: improve doc for saved timestamps etc.

Problem reported by Carpe Sébastien (Bug#24559).

1 files changed, 12 insertions, 6 deletions

diff --git a/gzip.1 b/gzip.1
index 05ed6d2..80a4bd3 100644
--- a/gzip.1
+++ b/gzip.1
@@ -183,12 +183,14 @@ or adaptive Huffman coding
 .PP
 Compression is always performed, even if the compressed file is
 slightly larger than the original. The worst case expansion is
-a few bytes for the gzip file header, plus 5 bytes every 32K block,
-or an expansion ratio of 0.015% for large files. Note that the actual
+a few bytes for the gzip file header, plus 5 bytes per 32\ KiB block,
+or an expansion ratio of 0.015% for large files. The actual
 number of used disk blocks almost never increases.
+.PP
 .B gzip
-preserves the mode, ownership and timestamps of files when compressing
-or decompressing.
+normally preserves the mode and modification timestamp
+of a file when compressing or decompressing. If you have appropriate
+privileges, it also preserves the file's owner and group.
 .SH OPTIONS
 .TP
 .B \-a --ascii
@@ -277,8 +279,12 @@ timestamp if present (copy it from the compressed file). This option
 is the default when decompressing.
 .TP
 .B \-N --name
-When compressing, always save the original file name and timestamp; this
-is the default. When decompressing, restore the original file name and
+When compressing, always save the original file name, and save
+the seconds part of the original modification timestamp if the
+original is a regular file and its timestamp is at least 1 (1970-01-01
+00:00:01 UTC) and is less than 2**32 (2106-02-07 06:28:16 UTC,
+assuming leap seconds are not counted); this
+is the default. When decompressing, restore from the saved file name and
 timestamp if present. This option is useful on systems which have
 a limit on file name length or when the timestamp has been lost after
 a file transfer.