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Standard C Library (libc.a, libc.so) Berkeley Compatibility Library (libbsd.a)
#include <unistd.h>
Interfaces documented on this reference page conform to industry standards as follows:
nice(): XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information about industry standards and associated tags.
The nice() function adds the value specified in the increment parameter to the nice value of the calling process. The nice value is a nonnegative number; a higher nice value gives the process a lower CPU priority.
When you are using the Standard C Library version of the nice() function, the maximum nice value for a process is 39 (2 * {NZERO} -1) and the minimum is 0 (zero). Requests for values outside these limits result in the nice value being set to the corresponding limit.
[XPG4-UNIX] If execution of the Standard C Library nice() function fails, the system does not alter the specified priority.
Any process can lower its priority (numerically raise its nice value). A process must have superuser privileges to raise its priority (numerically lower its nice value).
[Digital] For backward compatibility, a version of the nice() function is supported that allows nice values in the range of -20 to 20. Requests for values above or below these limits result in the nice value being set to the corresponding limit. To use the backward-compatible version of nice(), compile with the Berkeley Compatibility Library (libbsd.a).
Upon successful completion, the nice() function returns the new nice value minus 20 ({NZERO}). Otherwise, the function returns -1 and sets errno to indicate the error.
The Standard C Library version of nice() sets errno to the specified values for the following conditions: The calling process does not have appropriate privilege.
[Digital] The libbsd.a version of nice() sets errno to the same values as the setpriority() function. For information about possible return values for the setpriority() function, see setpriority(2).
Functions: exec(2), getpriority(2), setpriority(2)
Standards: standards(5) delim off