Linux Man Page Viewer
The following form allows you to view linux man pages.
getitimer
SYNOPSIS
#include <sys/time.h>
int getitimer(int which, struct itimerval *curr_value);
int setitimer(int which, const struct itimerval *new_value,
struct itimerval *old_value);
DESCRIPTION
The system provides each process with three interval timers, each
decrementing in a distinct time domain. When any timer expires, a sig-
nal is sent to the process, and the timer (potentially) restarts.
ITIMER_REAL decrements in real time, and delivers SIGALRM upon expi-
ration.
ITIMER_VIRTUAL decrements only when the process is executing, and
delivers SIGVTALRM upon expiration.
ITIMER_PROF decrements both when the process executes and when the
system is executing on behalf of the process. Coupled
with ITIMER_VIRTUAL, this timer is usually used to pro-
file the time spent by the application in user and ker-
nel space. SIGPROF is delivered upon expiration.
Timer values are defined by the following structures:
struct itimerval {
struct timeval it_interval; /* next value */
struct timeval it_value; /* current value */
};
struct timeval {
time_t tv_sec; /* seconds */
suseconds_t tv_usec; /* microseconds */
};
The function getitimer() fills the structure pointed to by curr_value
with the current setting for the timer specified by which (one of
ITIMER_REAL, ITIMER_VIRTUAL, or ITIMER_PROF). The element it_value is
set to the amount of time remaining on the timer, or zero if the timer
is disabled. Similarly, it_interval is set to the reset value.
The function setitimer() sets the specified timer to the value in
new_value. If old_value is non-NULL, the old value of the timer is
stored there.
Timers decrement from it_value to zero, generate a signal, and reset to
it_interval. A timer which is set to zero (it_value is zero or the
timer expires and it_interval is zero) stops.
Both tv_sec and tv_usec are significant in determining the duration of
a timer.
ERRORS
EFAULT new_value, old_value, or curr_value is not valid a pointer.
EINVAL which is not one of ITIMER_REAL, ITIMER_VIRTUAL, or ITIMER_PROF;
or (since Linux 2.6.22) one of the tv_usec fields in the struc-
ture pointed to by new_value contains a value outside the range
0 to 999999.
CONFORMING TO
POSIX.1-2001, SVr4, 4.4BSD (this call first appeared in 4.2BSD).
POSIX.1-2008 marks getitimer() and setitimer() obsolete, recommending
the use of the POSIX timers API (timer_gettime(2), timer_settime(2),
etc.) instead.
NOTES
A child created via fork(2) does not inherit its parent's interval
timers. Interval timers are preserved across an execve(2).
POSIX.1 leaves the interaction between setitimer() and the three inter-
faces alarm(2), sleep(3), and usleep(3) unspecified.
The standards are silent on the meaning of the call:
setitimer(which, NULL, &old_value);
Many systems (Solaris, the BSDs, and perhaps others) treat this as
equivalent to:
getitimer(which, &old_value);
In Linux, this is treated as being equivalent to a call in which the
new_value fields are zero; that is, the timer is disabled. Don't use
this Linux misfeature: it is nonportable and unnecessary.
BUGS
The generation and delivery of a signal are distinct, and only one
instance of each of the signals listed above may be pending for a pro-
cess. Under very heavy loading, an ITIMER_REAL timer may expire before
the signal from a previous expiration has been delivered. The second
signal in such an event will be lost.
On Linux kernels before 2.6.16, timer values are represented in
jiffies. If a request is made set a timer with a value whose jiffies
representation exceeds MAX_SEC_IN_JIFFIES (defined in
include/linux/jiffies.h), then the timer is silently truncated to this
ceiling value. On Linux/i386 (where, since Linux 2.6.13, the default
jiffy is 0.004 seconds), this means that the ceiling value for a timer
is approximately 99.42 days. Since Linux 2.6.16, the kernel uses a
different internal representation for times, and this ceiling is
removed.
On certain systems (including i386), Linux kernels before version
Linux 2012-10-01 GETITIMER(2)