1GETPRIORITY(3P) POSIX Programmer's Manual GETPRIORITY(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 getpriority, setpriority — get and set the nice value
13
15 #include <sys/resource.h>
16 int getpriority(int which, id_t who);
18 int setpriority(int which, id_t who, int value);
19
21 The getpriority() function shall obtain the nice value of a process,
22 process group, or user. The setpriority() function shall set the nice
23 value of a process, process group, or user to value+{NZERO}.
24 Target processes are specified by the values of the which and who argu‐
26 ments. The which argument may be one of the following values:
27 PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, indicating that the who argument
28 is to be interpreted as a process ID, a process group ID, or an effec‐
29 tive user ID, respectively. A 0 value for the who argument specifies
30 the current process, process group, or user.
31 The nice value set with setpriority() shall be applied to the process.
33 If the process is multi-threaded, the nice value shall affect all sys‐
34 tem scope threads in the process.
35 If more than one process is specified, getpriority() shall return value
37 {NZERO} less than the lowest nice value pertaining to any of the speci‐
38 fied processes, and setpriority() shall set the nice values of all of
39 the specified processes to value+{NZERO}.
40 The default nice value is {NZERO}; lower nice values shall cause more
42 favorable scheduling. While the range of valid nice values is
43 [0,{NZERO}*2-1], implementations may enforce more restrictive limits.
44 If value+{NZERO} is less than the system's lowest supported nice value,
45 setpriority() shall set the nice value to the lowest supported value;
46 if value+{NZERO} is greater than the system's highest supported nice
47 value, setpriority() shall set the nice value to the highest supported
48 value.
49 Only a process with appropriate privileges can lower its nice value.
51 Any processes or threads using SCHED_FIFO or SCHED_RR shall be unaf‐
53 fected by a call to setpriority(). This is not considered an error. A
54 process which subsequently reverts to SCHED_OTHER need not have its
55 priority affected by such a setpriority() call.
56 The effect of changing the nice value may vary depending on the
58 process-scheduling algorithm in effect.
59 Since getpriority() can return the value -1 upon successful completion,
61 it is necessary to set errno to 0 prior to a call to getpriority(). If
62 getpriority() returns the value -1, then errno can be checked to see if
63 an error occurred or if the value is a legitimate nice value.
64
66 Upon successful completion, getpriority() shall return an integer in
67 the range -{NZERO} to {NZERO}-1. Otherwise, -1 shall be returned and
68 errno set to indicate the error.
69 Upon successful completion, setpriority() shall return 0; otherwise, -1
71 shall be returned and errno set to indicate the error.
72
74 The getpriority() and setpriority() functions shall fail if:
75 ESRCH No process could be located using the which and who argument
77 values specified.
78 EINVAL The value of the which argument was not recognized, or the value
80 of the who argument is not a valid process ID, process group ID,
81 or user ID.
82 In addition, setpriority() may fail if:
84 EPERM A process was located, but neither the real nor effective user
86 ID of the executing process match the effective user ID of the
87 process whose nice value is being changed.
88 EACCES A request was made to change the nice value to a lower numeric
90 value and the current process does not have appropriate privi‐
91 leges.
92 The following sections are informative.
94
96 Using getpriority()
97 The following example returns the current scheduling priority for the
98 process ID returned by the call to getpid().
99 #include <sys/resource.h>
102 ...
103 int which = PRIO_PROCESS;
104 id_t pid;
105 int ret;
106 pid = getpid();
108 ret = getpriority(which, pid);
109 Using setpriority()
111 The following example sets the priority for the current process ID to
112 -20.
113 #include <sys/resource.h>
116 ...
117 int which = PRIO_PROCESS;
118 id_t pid;
119 int priority = -20;
120 int ret;
121 pid = getpid();
123 ret = setpriority(which, pid, priority);
124
126 The getpriority() and setpriority() functions work with an offset nice
127 value (nice value -{NZERO}). The nice value is in the range
128 [0,2*{NZERO} -1], while the return value for getpriority() and the
129 third parameter for setpriority() are in the range [-{NZERO},{NZERO}
130 -1].
131
133 None.
134
136 None.
137
139 nice(), sched_get_priority_max(), sched_setscheduler()
140 The Base Definitions volume of POSIX.1‐2017, <sys_resource.h>
142
144 Portions of this text are reprinted and reproduced in electronic form
145 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
146 table Operating System Interface (POSIX), The Open Group Base Specifi‐
147 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
148 Electrical and Electronics Engineers, Inc and The Open Group. In the
149 event of any discrepancy between this version and the original IEEE and
150 The Open Group Standard, the original IEEE and The Open Group Standard
151 is the referee document. The original Standard can be obtained online
152 at http://www.opengroup.org/unix/online.html .
153 Any typographical or formatting errors that appear in this page are
155 most likely to have been introduced during the conversion of the source
156 files to man page format. To report such errors, see https://www.ker‐
157 nel.org/doc/man-pages/reporting_bugs.html .
158IEEE/The Open Group 2017 GETPRIORITY(3P)