nice.2 (2010 09)

nice(2) nice(2)

NAME

nice - change priority of a process

SYNOPSIS

#include <unistd.h>

int nice(int priority_change);

DESCRIPTION

nice() adds the value of priority_change to the nice value of the calling process. A process’s nice value

is a positive number for which a more positive value results in lower CPU priority.

A maximum nice value of 39 and a minimum nice value of 0 are imposed by the system. Requests for

values above or below these limits result in the nice value being set to the corresponding limit.

If the calling process contains more than one thread or lightweight process (i.e., the process is multi-

threaded) this function shall apply to all threads or lightweight processes in the calling process.

Security Restrictions

Some or all of the actions associated with this system call are subject to compartmental restrictions. See

compartments (5) for more information about compartmentalization on systems that support that feature.

Compartmental restrictions can be overridden if the process possesses the

PRIV_COMMALLOWED

privilege (COMMALLOWED). Processes owned by the superuser may not have this privilege. Processes

owned by any user may have this privilege, depending on system conﬁguration.

Some or all of the actions associated with this system call require the

PRIV_OWNER (OWNER) and/or the

PRIV_LIMIT (LIMIT) privileges. Processes owned by the superuser will have these privileges. Processes

owned by other users may have privilege(s), depending on system conﬁguration. See privileges (5) for

more information about privileged access on systems that support ﬁne-grained privileges.

RETURN VALUE

Upon successful completion,

nice() returns the new nice value minus 20. Otherwise, a value of −1is

returned and

errno is set to indicate the error.

Note that

nice() assumes a user process priority value of 20. If a user having appropriate privileges

has changed the user process priority value to something less than 20, certain values for priority_change

can cause nice() to return −1, which is indistinguishable from an error return.

ERRORS

[EPERM]

nice() fails and does not change the nice value if priority_change is negative or greater

than 40, and the effective user ID of the calling process is not a user having appropriate

privileges.