NAME

setppri − set process priority

SYNOPSIS

int setppri (pid, pri)
int pid, pri;

DESCRIPTION

setppri sets the priority of the specified process to the indicated priority. 

Setting the process priority to a positive value has little effect since the normal system priority will quickly override whatever positive priority is set.  Setting the process priority to a negative value makes the process into a real-time process. 

Real-time processes are scheduled differently from normal processes.  Real-time processes never have their priority altered by the kernel.  Real-time processes are scheduled before any non real-time process and execute until either they voluntarily relinquish the CPU, another real-time process of higher (smaller numeric) priority becomes ready to run, or the process expires its time slice and another real-time process of the same priority is ready to run. 

The process nice value has no effect on real-time processes and the nice value does not affect real-time process priority values. 

Real-time processes can be quite dangerous, since a real-time process in an infinite loop cannot be interrupted by any other process (other than a real-time process of higher priority). 

setppri may be invoked only by the super-user. 

setppri fails if one or more of the following are true:

­[EINVAL] The pid does not correspond to any current process in the system. 

­[EINVAL] The pri value specified is not between -128 and +127, inclusive. 

SEE ALSO

nice(2)

DIAGNOSTICS

setppri returns zero on successful execution.  Otherwise a value of -1 is returned and errno is set to indicate the error. 

September 02, 1992