:man source: util-linux {release-version}
:page-layout: base
:command: flock
+:copyright: ©
== NAME
== COPYRIGHT
-Copyright © 2003-2006 H. Peter Anvin. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//TRANSLATORS: Keep {copyright} untranslated.
+Copyright {copyright} 2003-2006 H. Peter Anvin. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
== SEE ALSO
This epoch value is used whenever *hwclock* reads or sets the Hardware Clock on an Alpha machine. For ISA machines the kernel uses the fixed Hardware Clock epoch of 1900.
*--predict*::
-Predict what the Hardware Clock will read in the future based upon the time given by the *--date* option and the information in _{ADJTIME_PATH}_. This is useful, for example, to account for drift when setting a Hardware Clock wakeup (aka alarm). See *rtcwake*(8).
+Predict what the Hardware Clock will read in the future based upon the time given by the *--date* option and the information in _{ADJTIME_PATH}_. This is useful, for example, to account for drift when setting a Hardware Clock wakeup (aka alarm). See *rtcwake*(8).
+
Do not use this function if the Hardware Clock is being modified by anything other than the current operating system's *hwclock* command, such as '11 minute mode' or from dual-booting another OS.
*-r*, *--show*; *--get*::
-Read the Hardware Clock and print its time to standard output in the *ISO 8601* format. The time shown is always in local time, even if you keep your Hardware Clock in UTC. See the *--localtime* option.
+Read the Hardware Clock and print its time to standard output in the *ISO 8601* format. The time shown is always in local time, even if you keep your Hardware Clock in UTC. See the *--localtime* option.
+
Showing the Hardware Clock time is the default when no function is specified.
+
+
The System Clock must be kept in the UTC timescale for date-time applications to work correctly in conjunction with the timezone configured for the system. If the Hardware Clock is kept in local time then the time read from it must be shifted to the UTC timescale before using it to set the System Clock. The *--hctosys* function does this based upon the information in the _{ADJTIME_PATH}_ file or the command line arguments *--localtime* and *--utc*. Note: no daylight saving adjustment is made. See the discussion below, under *LOCAL vs UTC*.
+
-The kernel also keeps a timezone value, the *--hctosys* function sets it to the timezone configured for the system. The system timezone is configured by the TZ environment variable or the _/etc/localtime_ file, as *tzset*(3) would interpret them. The obsolete _tz_dsttime_ field of the kernel's timezone value is set to zero. (For details on what this field used to mean, see *settimeofday*(2).)
+The kernel also keeps a timezone value, the *--hctosys* function sets it to the timezone configured for the system. The system timezone is configured by the TZ environment variable or the _/etc/localtime_ file, as *tzset*(3) would interpret them. The obsolete _tz_dsttime_ field of the kernel's timezone value is set to zero. (For details on what this field used to mean, see *settimeofday*(2).)
+
When used in a startup script, making the *--hctosys* function the first caller of *settimeofday*(2) from boot, it will set the NTP '11 minute mode' timescale via the _persistent_clock_is_local_ kernel variable. If the Hardware Clock's timescale configuration is changed then a reboot is required to inform the kernel. See the discussion below, under *Automatic Hardware Clock Synchronization by the Kernel*.
+
The first two are only available on the first call of *settimeofday*(2) after boot. Consequently this option only makes sense when used in a startup script. If the Hardware Clocks timescale configuration is changed then a reboot would be required to inform the kernel.
*-w*, *--systohc*::
-Set the Hardware Clock from the System Clock, and update the timestamps in _{ADJTIME_PATH}_. With the *--update-drift* option also (re)calculate the drift factor. Try it without the option if *--systohc* fails. See *--update-drift* below.
+Set the Hardware Clock from the System Clock, and update the timestamps in _{ADJTIME_PATH}_. With the *--update-drift* option also (re)calculate the drift factor. Try it without the option if *--systohc* fails. See *--update-drift* below.
*-V*, *--version*::
Display version information and exit.
*noauto*::
Can only be mounted explicitly (i.e., the *-a* option will not cause the filesystem to be mounted).
-**context=**__context__, **fscontext=**__context__, **defcontext=**__context__, and **rootcontext=**__context__::
+**context=**__context__, **fscontext=**__context__, **defcontext=**__context__, and **rootcontext=**__context__::
The *context=* option is useful when mounting filesystems that do not support extended attributes, such as a floppy or hard disk formatted with VFAT, or systems that are not normally running under SELinux, such as an ext3 or ext4 formatted disk from a non-SELinux workstation. You can also use *context=* on filesystems you do not trust, such as a floppy. It also helps in compatibility with xattr-supporting filesystems on earlier 2.4.<x> kernel versions. Even where xattrs are supported, you can save time not having to label every file by assigning the entire disk one security context.
+
-A commonly used option for removable media is *context="system_u:object_r:removable_t*.
+A commonly used option for removable media is *context="system_u:object_r:removable_t*.
+
Two other options are *fscontext=* and *defcontext=*, both of which are mutually exclusive of the *context=* option. This means you can use fscontext and defcontext with each other, but neither can be used with context.
+
*relatime*::
Update inode access times relative to modify or change time. Access time is only updated if the previous access time was earlier than the current modify or change time. (Similar to *noatime*, but it doesn't break *mutt*(1) or other applications that need to know if a file has been read since the last time it was modified.)
+
-Since Linux 2.6.30, the kernel defaults to the behavior provided by this option (unless *noatime* was specified), and the *strictatime* option is required to obtain traditional semantics. In addition, since Linux 2.6.30, the file's last access time is always updated if it is more than 1 day old.
+Since Linux 2.6.30, the kernel defaults to the behavior provided by this option (unless *noatime* was specified), and the *strictatime* option is required to obtain traditional semantics. In addition, since Linux 2.6.30, the file's last access time is always updated if it is more than 1 day old.
*norelatime*::
Do not use the *relatime* feature. See also the *strictatime* mount option.
*strictatime*::
-Allows to explicitly request full atime updates. This makes it possible for the kernel to default to *relatime* or *noatime* but still allow userspace to override it. For more details about the default system mount options see _/proc/mounts_.
+Allows to explicitly request full atime updates. This makes it possible for the kernel to default to *relatime* or *noatime* but still allow userspace to override it. For more details about the default system mount options see _/proc/mounts_.
*nostrictatime*::
Use the kernel's default behavior for inode access time updates.
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