1GETPRIORITY(2) Linux Programmer's Manual GETPRIORITY(2)
2
6 getpriority, setpriority - get/set program scheduling priority
7
9 #include <sys/time.h>
10 #include <sys/resource.h>
11 int getpriority(int which, id_t who);
13 int setpriority(int which, id_t who, int prio);
14
16 The scheduling priority of the process, process group, or user, as in‐
17 dicated by which and who is obtained with the getpriority() call and
18 set with the setpriority() call. The process attribute dealt with by
19 these system calls is the same attribute (also known as the "nice"
20 value) that is dealt with by nice(2).
21 The value which is one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, and
23 who is interpreted relative to which (a process identifier for
24 PRIO_PROCESS, process group identifier for PRIO_PGRP, and a user ID for
25 PRIO_USER). A zero value for who denotes (respectively) the calling
26 process, the process group of the calling process, or the real user ID
27 of the calling process.
28 The prio argument is a value in the range -20 to 19 (but see NOTES be‐
30 low). with -20 being the highest priority and 19 being the lowest pri‐
31 ority. Attempts to set a priority outside this range are silently
32 clamped to the range. The default priority is 0; lower values give a
33 process a higher scheduling priority.
34 The getpriority() call returns the highest priority (lowest numerical
36 value) enjoyed by any of the specified processes. The setpriority()
37 call sets the priorities of all of the specified processes to the spec‐
38 ified value.
39 Traditionally, only a privileged process could lower the nice value
41 (i.e., set a higher priority). However, since Linux 2.6.12, an unpriv‐
42 ileged process can decrease the nice value of a target process that has
43 a suitable RLIMIT_NICE soft limit; see getrlimit(2) for details.
44
46 On success, getpriority() returns the calling thread's nice value,
47 which may be a negative number. On error, it returns -1 and sets errno
48 to indicate the cause of the error.
49 Since a successful call to getpriority() can legitimately return the
51 value -1, it is necessary to clear the external variable errno prior to
52 the call, then check errno afterward to determine if -1 is an error or
53 a legitimate value.
54 setpriority() returns 0 on success. On error, it returns -1 and sets
56 errno to indicate the cause of the error.
57
59 EINVAL which was not one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER.
60 ESRCH No process was located using the which and who values specified.
62 In addition to the errors indicated above, setpriority() may fail if:
64 EACCES The caller attempted to set a lower nice value (i.e., a higher
66 process priority), but did not have the required privilege (on
67 Linux: did not have the CAP_SYS_NICE capability).
68 EPERM A process was located, but its effective user ID did not match
70