mirror of https://github.com/mkerrisk/man-pages
218 lines
6.2 KiB
Groff
218 lines
6.2 KiB
Groff
.\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.TH TIMER_SETTIME 2 2021-03-22 Linux "Linux Programmer's Manual"
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.SH NAME
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timer_settime, timer_gettime \- arm/disarm and fetch
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state of POSIX per-process timer
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.SH SYNOPSIS
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.nf
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.B #include <time.h>
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.PP
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.BI "int timer_settime(timer_t " timerid ", int " flags ,
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.BI " const struct itimerspec *restrict " new_value ,
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.BI " struct itimerspec *restrict " old_value );
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.BI "int timer_gettime(timer_t " timerid ", struct itimerspec *" curr_value );
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.fi
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.PP
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Link with \fI\-lrt\fP.
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.PP
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.RS -4
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.RE
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.PP
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.BR timer_settime (),
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.BR timer_gettime ():
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.nf
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_POSIX_C_SOURCE >= 199309L
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.fi
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.SH DESCRIPTION
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.BR timer_settime ()
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arms or disarms the timer identified by
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.IR timerid .
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The
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.I new_value
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argument is pointer to an
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.I itimerspec
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structure that specifies the new initial value and
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the new interval for the timer.
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The
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.I itimerspec
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structure is defined as follows:
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.PP
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.in +4n
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.EX
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struct timespec {
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time_t tv_sec; /* Seconds */
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long tv_nsec; /* Nanoseconds */
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};
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struct itimerspec {
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struct timespec it_interval; /* Timer interval */
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struct timespec it_value; /* Initial expiration */
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};
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.EE
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.in
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.PP
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Each of the substructures of the
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.I itimerspec
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structure is a
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.I timespec
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structure that allows a time value to be specified
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in seconds and nanoseconds.
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These time values are measured according to the clock
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that was specified when the timer was created by
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.BR timer_create (2).
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.PP
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If
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.I new_value\->it_value
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specifies a nonzero value (i.e., either subfield is nonzero), then
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.BR timer_settime ()
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arms (starts) the timer,
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setting it to initially expire at the given time.
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(If the timer was already armed,
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then the previous settings are overwritten.)
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If
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.I new_value\->it_value
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specifies a zero value
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(i.e., both subfields are zero),
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then the timer is disarmed.
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.PP
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The
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.I new_value\->it_interval
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field specifies the period of the timer, in seconds and nanoseconds.
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If this field is nonzero, then each time that an armed timer expires,
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the timer is reloaded from the value specified in
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.IR new_value\->it_interval .
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If
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.I new_value\->it_interval
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specifies a zero value,
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then the timer expires just once, at the time specified by
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.IR it_value .
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.PP
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By default, the initial expiration time specified in
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.I new_value\->it_value
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is interpreted relative to the current time on the timer's
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clock at the time of the call.
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This can be modified by specifying
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.B TIMER_ABSTIME
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in
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.IR flags ,
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in which case
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.I new_value\->it_value
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is interpreted as an absolute value as measured on the timer's clock;
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that is, the timer will expire when the clock value reaches the
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value specified by
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.IR new_value\->it_value .
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If the specified absolute time has already passed,
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then the timer expires immediately,
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and the overrun count (see
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.BR timer_getoverrun (2))
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will be set correctly.
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.\" By experiment: the overrun count is set correctly, for CLOCK_REALTIME.
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.PP
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If the value of the
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.B CLOCK_REALTIME
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clock is adjusted while an absolute timer based on that clock is armed,
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then the expiration of the timer will be appropriately adjusted.
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Adjustments to the
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.B CLOCK_REALTIME
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clock have no effect on relative timers based on that clock.
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.\" Similar remarks might apply with respect to process and thread CPU time
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.\" clocks, but these clocks are not currently (2.6.28) settable on Linux.
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.PP
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If
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.I old_value
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is not NULL, then it points to a buffer
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that is used to return the previous interval of the timer (in
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.IR old_value\->it_interval )
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and the amount of time until the timer
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would previously have next expired (in
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.IR old_value\->it_value ).
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.PP
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.BR timer_gettime ()
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returns the time until next expiration, and the interval,
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for the timer specified by
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.IR timerid ,
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in the buffer pointed to by
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.IR curr_value .
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The time remaining until the next timer expiration is returned in
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.IR curr_value\->it_value ;
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this is always a relative value, regardless of whether the
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.BR TIMER_ABSTIME
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flag was used when arming the timer.
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If the value returned in
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.IR curr_value\->it_value
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is zero, then the timer is currently disarmed.
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The timer interval is returned in
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.IR curr_value\->it_interval .
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If the value returned in
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.IR curr_value\->it_interval
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is zero, then this is a "one-shot" timer.
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.SH RETURN VALUE
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On success,
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.BR timer_settime ()
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and
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.BR timer_gettime ()
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return 0.
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On error, \-1 is returned, and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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These functions may fail with the following errors:
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.TP
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.B EFAULT
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.IR new_value ,
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.IR old_value ,
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or
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.I curr_value
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is not a valid pointer.
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.TP
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.B EINVAL
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.I timerid
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is invalid.
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.\" FIXME . eventually: invalid value in flags
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.PP
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.BR timer_settime ()
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may fail with the following errors:
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.TP
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.B EINVAL
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.I new_value.it_value
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is negative; or
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.I new_value.it_value.tv_nsec
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is negative or greater than 999,999,999.
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.SH VERSIONS
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These system calls are available since Linux 2.6.
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.SH CONFORMING TO
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POSIX.1-2001, POSIX.1-2008.
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.SH EXAMPLES
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See
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.BR timer_create (2).
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.SH SEE ALSO
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.BR timer_create (2),
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.BR timer_getoverrun (2),
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.BR time (7)
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