Probably, it's not wise to suggest adjtime(3) as the more
portable API. Rather, ntp_adjtime(3) should be used.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Starting with Linux 3.4, the time_state change is now asynchronous
and the call returns the time_state before it has been altered,
rather than after it was altered as the previous code did.
======================================================
Notes from Petr Gajdos
attached program behaves differently on 2.6 and 3.0 kernels:
*******************************************************
2.6.32.59-0.7-default
Insert LS
adjtimex() return code 1: insert leap second (TIME_INS)
Kernel leap second flag: STA_INS
Delete LS
adjtimex() return code 2: delete leap second (TIME_DEL)
Kernel leap second flag: STA_DEL
Insert LS again
adjtimex() return code 1: insert leap second (TIME_INS)
Kernel leap second flag: STA_INS
Delete LS again
adjtimex() return code 2: delete leap second (TIME_DEL)
Kernel leap second flag: STA_DEL
*******************************************************
3.0.101-0.35-default
sbsvt101:~/tmp # ./adjt
Insert LS
adjtimex() return code 0: clock synchronized (TIME_OK)
Kernel leap second flag: STA_INS
Delete LS
adjtimex() return code 1: insert leap second (TIME_INS)
Kernel leap second flag: STA_DEL
Insert LS again
adjtimex() return code 2: delete leap second (TIME_DEL)
Kernel leap second flag: STA_INS
Delete LS again
adjtimex() return code 1: insert leap second (TIME_INS)
Kernel leap second flag: STA_DEL
*******************************************************
The explanation provided by William Preston (in CC):
"""
in both cases you get the actual value of the global kernel variable
time_state.
The code changed between the two kernels in the way it handled this.
In 2.6.32.59 the adjtimex call starts a timer immediately with the
function ntp_start_leap_timer(), which sets the value of time_state
before returning to the user.
This means you will get the value TIME_INS / TIME_DEL back
immediately.
In 3.0.101, the timer has been removed and the value of time_state is
set when the microsecond field overflows. The function
second_overflow() handles this. This means the value of time_state
will not have been set when the syscall adjtimex returns, and so you
will almost certainly get the old state.
Incidentally if you remove the sleep() calls in the code for 3.0.101
you may instead see the state of TIME_OK when switching between
STA_INS / STA_DEL.
All this is completely normal and expected behaviour, since both
return the current state, however I agree it is not intuitive.
I would recommend calling adjtimex without a mode to get the actual
state of the system after waiting a second.
At the same time, William suggests the patch in the attachement.
Petr
=============== adjt.c ================
void adjtm(int);
int main()
{
printf("Insert LS\n");
adjtm(STA_INS);
sleep(2);
printf("\nDelete LS\n");
adjtm(STA_DEL);
sleep(2);
printf("\nInsert LS again\n");
adjtm(STA_INS);
sleep(2);
printf("\nDelete LS again\n");
adjtm(STA_DEL);
printf("\nRestoring initial state\n");
adjtm(0);
}
/*************************************/
/* Modify LS flag and print status */
/*************************************/
void adjtm(int ls)
{
struct timex tx;
int rc;
tx.modes = ADJ_STATUS;
tx.status = ls;
if ((rc = adjtimex(&tx)) == -1) {
perror("adjtimex()");
exit(1);
}
sleep(2);
tx.modes = 0;
rc = adjtimex(&tx);
printf("adjtimex() return code %d: ", rc);
switch (rc) {
case TIME_OK:
printf("clock synchronized (TIME_OK)\n");
break;
case TIME_INS:
printf("insert leap second (TIME_INS)\n");
break;
case TIME_DEL:
printf("delete leap second (TIME_DEL)\n");
break;
case TIME_OOP:
printf("leap second in progress (TIME_OOP)\n");
break;
case TIME_WAIT:
printf("leap second has occurred (TIME_WAIT)\n");
break;
case TIME_BAD:
printf("clock not synchronized (TIME_BAD)\n");
break;
default:
printf("Unknown return code: %i\n", rc);
break;
}
printf("Kernel leap second flag: ");
if (tx.status & STA_INS)
printf("STA_INS\n");
else if (tx.status & STA_DEL)
printf("STA_DEL\n");
else
printf("not set\n");
}
=======================================
Reported-by: Petr Gajdos <pgajdos@suse.cz>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
_POSIX_SOURCE was a POSIX.1-1990 creation that was soon made
obsolete bu _POSIX_C_SOURCE. Retaining mention of it
in the feature test macro requirements section of the
SYNOPSIS doesn't contain important information, and may
mislead readers into actually trying to use this macro.
A few mentions of it a maintained in a some pages where
defining _POSIX_SOURCE inhibits some behavior.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Also remove redundant text covering FTM details that
are already provided in feature_test_macros(7).
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The right way to expose declarations for these Linux-specific
system calls was always _GNU_SOURCE. Mentioning the historical
use of _BSD_SOURCE and _SVID_SOURCE just clouds the issue.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Under the FTM requirements all of these pages document the
requirement for _ISOC99_SOURCE. And feature_test_macros(7) now
documents that "cc -std=c99" produces the same effect as defining
_ISOC99_SOURCE. So, all of these pages don't additionally need
to specify "or 'cc -std=c99'" under the FTM requirements
in the SYNOPSIS. Removing that redundant text also simplifies
the SYNOPSIS a little.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
_XOPEN_SOURCE_EXTENDED is obsolete (it existed in SUSv1, but not
subsequent standards). _XOPEN_SOURCE >= 500 produces the same
effects as (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED). Modifying
the SYNOPSIS of various ages that contain:
_XOPEN_SOURCE\ >=\ 500 ||
_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
to just:
_XOPEN_SOURCE\ >=\ 500
This has the following benefits:
a) Simplifying the SYNOPSIS by removing ancient
historical information.
b) Preventing users from being misled into using
_XOPEN_SOURCE_EXTENDED in new source code.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
It seems that adjtimex() never needed _BSD_SOURCE (and my
earlier commit 5918743bc8 was simply a blunder.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Looking at <features.h> (or feature_test_macros(7)), one can
see that when _XOPEN_SOURCE is defined with the value 700
(or greater), then _POSIX_C_SOURCE is defined with the value
200809L (or greater). Therefore, terms in the man pages such as
_XOPEN_SOURCE\ >=\ 700 || _POSIX_C_SOURCE\ >=\ 200809L
can be simpified to:
_POSIX_C_SOURCE\ >=\ 200809L
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Looking at <features.h> (or feature_test_macros(7)), one can
see that when _XOPEN_SOURCE is defined with the value 600
(or greater), then _POSIX_C_SOURCE is defined with the value
200112L (or greater). Therefore, terms in the man pages such as
_XOPEN_SOURCE\ >=\ 600 || _POSIX_C_SOURCE\ >=\ 200112L
can be simplified to:
_POSIX_C_SOURCE\ >=\ 200112L
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>`
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Looking at <features.h> (or feature_test_macros(7)), one can
see that when _XOPEN_SOURCE is defined with the value 600
(or greater), then _POSIX_C_SOURCE is defined with the value
200112L (or greater). Therefore, terms in the man pages such as
_XOPEN_SOURCE\ >=\ 600 || _POSIX_C_SOURCE\ >=\ 200112L
can be simpified to:
_POSIX_C_SOURCE\ >=\ 200112L
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Update to use _DEFAULT_SOURCE, and also changes brought by
glibc commit 266865c0e7b79d4196e2cc393693463f03c90bd8.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The text has an incorrect description in NOTES, it says
that (2^32/HZ) - 300 is about 429 million. It is correct
only if HZ=10 which does not look common today. So just
removing "(i.e., about 429 million)" is good enough.
----
Signed-off-by: Naoya Kondo <kondo-naoya@jp.fujitsu.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This man page did not make it obvious which functions
should be used for manipulating signals sets, nor where
those functions were documented.
Reported-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Document the MADV_FREE flag added to madvise() in Linux 4.5.
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Exceptionally, the lists on this page are in kernel version order
rather than alphabetical order. But one entry was out of order.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Light reworking of text proposed by Josh Triplett.
Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Light reworking of text proposed by Josh Triplett.
Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Michael Kerrisk