|GETPRIORITY(2)||Linux Programmer's Manual||GETPRIORITY(2)|
NAMEgetpriority, setpriority - get/set program scheduling priority
DESCRIPTIONThe scheduling priority of the process, process group, or user, as indicated by which and who is obtained with the getpriority() call and set with the setpriority() call.
RETURN VALUESince getpriority() can legitimately return the value -1, it is necessary to clear the external variable errno prior to the call, then check it afterward to determine if -1 is an error or a legitimate value. The setpriority() call returns 0 if there is no error, or -1 if there is.
- which was not one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER.
- No process was located using the which and who values specified.
In addition to the errors indicated above, setpriority() may fail if:
- The caller attempted to lower a process priority, but did not have the required privilege (on Linux: did not have the CAP_SYS_NICE capability). Since Linux 2.6.12, this error occurs only if the caller attempts to set a process priority outside the range of the RLIMIT_NICE soft resource limit of the target process; see getrlimit(2) for details.
- A process was located, but its effective user ID did not match either the effective or the real user ID of the caller, and was not privileged (on Linux: did not have the CAP_SYS_NICE capability). But see NOTES below.
CONFORMING TOSVr4, 4.4BSD (these function calls first appeared in 4.2BSD), POSIX.1-2001.
NOTESA child created by fork(2) inherits its parent's nice value. The nice value is preserved across execve(2).
The actual priority range varies between kernel versions. Linux before 1.3.36 had -infinity..15. Since kernel 1.3.43, Linux has the range -20..19. Within the kernel, nice values are actually represented using the corresponding range 40..1 (since negative numbers are error codes) and these are the values employed by the setpriority() and getpriority() system calls. The glibc wrapper functions for these system calls handle the translations between the user-land and kernel representations of the nice value according to the formula unice = 20 - knice.
On some systems, the range of nice values is -20..20.
Including <sys/time.h> is not required these days, but increases portability. (Indeed, <sys/resource.h> defines the rusage structure with fields of type struct timeval defined in <sys/time.h>.)
BUGSAccording to POSIX, the nice value is a per-process setting. However, under the current Linux/NPTL implementation of POSIX threads, the nice value is a per-thread attribute: different threads in the same process can have different nice values. Portable applications should avoid relying on the Linux behavior, which may be made standards conformant in the future.
SEE ALSOnice(1), renice(1), fork(2), capabilities(7)
COLOPHONThis page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.