On Jun 12, 2014, at 3:25 PM, Andrei POPESCU wrote: > Just to make it clear what we are talking about: > > - hardware clock: the time of your computer's internal clock, should be > UTC, but local time is also possible > - system time: the system's internal reference, is always UTC, is > usually *not* shown to users (unless you choose UTC as timezone) > - user time: (not sure this is the correct name) basically system time + > timezone > > Please note the timezone can be adjusted system-wide by the admin *and* > individually by each user.
Just to add a little more technical detail (If you don't find it useful, feel free to ignore it): The "hardware clock" is a chip on the motherboard, very similar to the chip in a digital wrist-watch. It can be read by the BIOS at boot time. It (usually) has no idea of anything related to time zones. It just bumps up a counter once per second and satisfies read/write requests from/to that counter when asked by either the BIOS or OS software. The counter is (usually) represented in base 365/24/60/60, not binary. This means that the hardware clock's timezone is maintained purely in software (Usually the OS. Only very occasionally the BIOS.) The "system clock" is set by the OS software from the hardware clock at boot time. The OS reads the hardware clock and adds/subtracts a timezone offset based on information stored in (at least for most modern Debaians) the /etc/adjtime and /etc/timezone files. This adjustment gives it UTC, which is used to set the system clock to UTC at boot-up. The system clock is always kept in UTC, but the library routines that read/write it take notice of the /etc/timezone file and of the TZ environment variable to display it according to the appropriate local timezone offset. This adjusted time, taking account of the user's requested timezone, is what Andrei is calling "User time". I don't know of a better name for it -- it's usually the object of some circumlocution like "What the user sees when she/he types the date(1) command". Hope this helps! Rick -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: https://lists.debian.org/120c1f9d-9466-480e-85aa-a41f71ba3...@pobox.com
