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clock_getres.2: Clarify difference between CLOCK_MONOTONIC and CLOCK_MONOTONIC_RAW 

Note interactions of these two clocks with discontinuous
adjustments to the system time and NTP/adjtime(2).

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2012-04-25 13:02:36 +12:00
parent 5f04b9486b
commit 63f0f3d9b8
1 changed files with 11 additions and 4 deletions
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15
man2/clock_getres.2
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@ -29,7 +29,7 @@
.\"
.\" FIXME: Linux 2.6.39 adds CLOCK_BOOTTIME
.\"
.TH CLOCK_GETRES 2 2010-02-03 "" "Linux Programmer's Manual"
.TH CLOCK_GETRES 2 2012-04-25 "" "Linux Programmer's Manual"
.SH NAME
clock_getres, clock_gettime, clock_settime \- clock and time functions
.SH SYNOPSIS
@ -128,13 +128,20 @@ Setting this clock requires appropriate privileges.
.B CLOCK_MONOTONIC
Clock that cannot be set and represents monotonic time since
some unspecified starting point.
This clock is not affected by discontinuous jumps in the system time
(e.g., if the system administrator manually changes the clock),
but is affected by the incremental adjustments performed by
.BR adjtime (2)
and NTP.
.TP
.BR CLOCK_MONOTONIC_RAW " (since Linux 2.6.28; Linux-specific)"
.\" Added in commit 2d42244ae71d6c7b0884b5664cf2eda30fb2ae68, John Stultz
Similar to
.BR CLOCK_MONOTONIC ,
but provides access to a raw hardware-based time
that is not subject to NTP adjustments.
that is not subject to NTP adjustments or
the incremental adjustments performed by
.BR adjtime (2).
.TP
.B CLOCK_PROCESS_CPUTIME_ID
High-resolution per-process timer from the CPU.
@ -227,7 +234,7 @@ On Linux, these clocks are not settable
.\" See http://bugzilla.kernel.org/show_bug.cgi?id=11972
.SH "SEE ALSO"
.BR date (1),
.BR adjtimex (2),
.BR adjtime (2),
.BR gettimeofday (2),
.BR settimeofday (2),
.BR time (2),
@ -236,4 +243,4 @@ On Linux, these clocks are not settable
.BR ftime (3),
.BR pthread_getcpuclockid (3),
.BR sysconf (3),
.BR time (7)
time (7)