diff options
| -rw-r--r-- | doc/coreutils.texi | 37 |
1 files changed, 33 insertions, 4 deletions
diff --git a/doc/coreutils.texi b/doc/coreutils.texi index 369fad2f9..c26a53d5d 100644 --- a/doc/coreutils.texi +++ b/doc/coreutils.texi @@ -7199,6 +7199,7 @@ a date like @samp{Mar 30@ @ 2002} for non-recent timestamps, and a date-without-year and time like @samp{Mar 30 23:45} for recent timestamps. This format can change depending on the current locale as detailed below. +@cindex clock skew A timestamp is considered to be @dfn{recent} if it is less than six months old, and is not dated in the future. If a timestamp dated today is not listed in recent form, the timestamp is in the future, @@ -10261,11 +10262,39 @@ A @var{file} argument string of @samp{-} is handled specially and causes @command{touch} to change the times of the file associated with standard output. +@cindex clock skew +By default, @command{touch} sets file timestamps to the current time. +Because @command{touch} acts on its operands left to right, the +resulting timestamps of earlier and later operands may disagree. +Also, the determination of what time is ``current'' depends on the +platform. Platforms with network file systems often use different +clocks for the operating system and for file systems; because +@command{touch} typically uses file systems' clocks by default, clock +skew can cause the resulting file timestamps to appear to be in a +program's ``future'' or ``past''. + +@cindex file timestamp resolution +The @command{touch} command sets the file's timestamp to the greatest +representable value that is not greater than the requested time. This +can differ from the requested time for several reasons. First, the +requested time may have a higher resolution than supported. Second, a +file system may use different resolutions for different types of +times. Third, file timestamps may use a different resolution than +operating system timestamps. Fourth, the operating system primitives +used to update timestamps may employ yet a different resolution. For +example, in theory a file system might use 10-microsecond resolution +for access time and 100-nanosecond resolution for modification time, +and the operating system might use nanosecond resolution for the +current time and microsecond resolution for the primitive that +@command{touch} uses to set a file's timestamp to an arbitrary value. + @cindex permissions, for changing file timestamps -If changing both the access and modification times to the current -time, @command{touch} can change the timestamps for files that the user -running it does not own but has write permission for. Otherwise, the -user must own the files. +When setting file timestamps to the current time, @command{touch} can +change the timestamps for files that the user does not own but has +write permission for. Otherwise, the user must own the files. Some +older systems have a further restriction: the user must own the files +unless both the access and modification times are being set to the +current time. Although @command{touch} provides options for changing two of the times---the times of last access and modification---of a file, there is actually |