pid is zero, the time quantum for the calling process is written
The identified process should be running under the
POSIX systems on which
is available define
On error, -1 is returned, and
is set appropriately.
Problem with copying information to userspace.
The system call is not yet implemented (only on rather old kernels).
The process whose ID is pid could not be found.
POSIX does not specify any mechanism for controlling the size of the
round-robin time quantum.
However, Linux provides a (nonportable) method of doing this.
The quantum can be controlled by adjusting the process's nice value (see
Assigning a negative (i.e., high) nice value results in a longer quantum;
assigning a positive (i.e., low) nice value results in a shorter quantum.
The default quantum is 0.1 seconds;
the degree to which changing the nice value affects the
quantum has varied somewhat across kernel versions.