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[thirdparty/man-pages.git] / man2 / getpriority.2

diff --git a/man2/getpriority.2 b/man2/getpriority.2
index dc12a833715f133c469daa4cc9ef3ba3d9f0c696..1efde47f24f95d034698fc60d2d7a5fec6943615 100644 (file)
--- a/man2/getpriority.2
+++ b/man2/getpriority.2
@@ -1,6 +1,7 @@
 .\" Copyright (c) 1980, 1991 The Regents of the University of California.
 .\" All rights reserved.
 .\"
 .\" Copyright (c) 1980, 1991 The Regents of the University of California.
 .\" All rights reserved.
 .\"

+.\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)

 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
 .\" are met:
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
 .\" are met:


@@ -28,19 +29,20 @@
 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.

+.\" %%%LICENSE_END

 .\"
 .\"     @(#)getpriority.2      6.9 (Berkeley) 3/10/91
 .\"
 .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
 .\" Modified 1996-07-01 by Andries Brouwer <aeb@cwi.nl>
 .\" Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>
 .\"
 .\"     @(#)getpriority.2      6.9 (Berkeley) 3/10/91
 .\"
 .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
 .\" Modified 1996-07-01 by Andries Brouwer <aeb@cwi.nl>
 .\" Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>

-.\" Modified 2001-10-21 by Michael Kerrisk <mtk-manpages@gmx.net>
+.\" Modified 2001-10-21 by Michael Kerrisk <mtk.manpages@gmail.com>

 .\"    Corrected statement under EPERM to clarify privileges required
 .\"    Corrected statement under EPERM to clarify privileges required

-.\" Modified 2002-06-21 by Michael Kerrisk <mtk-manpages@gmx.net>
+.\" Modified 2002-06-21 by Michael Kerrisk <mtk.manpages@gmail.com>

 .\"    Clarified meaning of 0 value for 'who' argument
 .\"    Clarified meaning of 0 value for 'who' argument

-.\" Modified 2004-05-27 by Michael Kerrisk <mtk-manpages@gmx.net>
+.\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>

 .\"
 .\"

-.TH GETPRIORITY 2 2002-06-21 "BSD Man Page" "Linux Programmer's Manual"
+.TH GETPRIORITY 2 2016-12-12 "Linux" "Linux Programmer's Manual"

 .SH NAME
 getpriority, setpriority \- get/set program scheduling priority
 .SH SYNOPSIS
 .SH NAME
 getpriority, setpriority \- get/set program scheduling priority
 .SH SYNOPSIS


@@ -48,9 +50,9 @@ getpriority, setpriority \- get/set program scheduling priority
 .br
 .B #include <sys/resource.h>
 .sp
 .br
 .B #include <sys/resource.h>
 .sp

-.BI "int getpriority(int " which ", int " who );
+.BI "int getpriority(int " which ", id_t " who );

 .br
 .br

-.BI "int setpriority(int " which ", int " who ", int " prio );
+.BI "int setpriority(int " which ", id_t " who ", int " prio );

 .SH DESCRIPTION
 The scheduling priority of the process, process group, or user, as
 indicated by
 .SH DESCRIPTION
 The scheduling priority of the process, process group, or user, as
 indicated by


@@ -58,10 +60,13 @@ indicated by
 and
 .I who
 is obtained with the
 and
 .I who
 is obtained with the

-.B getpriority
+.BR getpriority ()

 call and set with the
 call and set with the

-.B setpriority
+.BR setpriority ()

 call.
 call.

+The process attribute dealt with by these system calls is
+the same attribute (also known as the "nice" value) that is dealt with by
+.BR nice (2).

 
 The value
 .I which
 
 The value
 .I which


@@ -70,9 +75,9 @@ is one of
 .BR PRIO_PGRP ,
 or
 .BR PRIO_USER ,
 .BR PRIO_PGRP ,
 or
 .BR PRIO_USER ,

-and 
+and

 .I who
 .I who

-is interpreted relative to 
+is interpreted relative to

 .I which
 (a process identifier for
 .BR PRIO_PROCESS ,
 .I which
 (a process identifier for
 .BR PRIO_PROCESS ,


@@ -85,31 +90,54 @@ A zero value for
 .I who
 denotes (respectively) the calling process, the process group of the
 calling process, or the real user ID of the calling process.
 .I who
 denotes (respectively) the calling process, the process group of the
 calling process, or the real user ID of the calling process.

-.I Prio
-is a value in the range \-20 to 19 (but see the Notes below).
+
+The
+.I prio
+argument is a value in the range \-20 to 19 (but see NOTES below).
+with \-20 being the highest priority and 19 being the lowest priority.
+Attempts to set a priority outside this range
+are silently clamped to the range.

 The default priority is 0;
 The default priority is 0;

-lower priorities cause more favorable scheduling.
+lower values give a process a higher scheduling priority.

 
 The
 
 The

-.B getpriority
+.BR getpriority ()

 call returns the highest priority (lowest numerical value)
 call returns the highest priority (lowest numerical value)

-enjoyed by any of the specified processes.  The
-.B setpriority
+enjoyed by any of the specified processes.
+The
+.BR setpriority ()

 call sets the priorities of all of the specified processes
 call sets the priorities of all of the specified processes

-to the specified value.  Only the superuser may lower priorities.
-.SH "RETURN VALUE"
-Since
-.B getpriority
+to the specified value.
+
+Traditionally, only a privileged process could lower the nice value
+(i.e., set a higher priority).
+However, since Linux 2.6.12, an unprivileged process can decrease
+the nice value of a target process that has a suitable
+.BR RLIMIT_NICE
+soft limit; see
+.BR getrlimit (2)
+for details.
+.SH RETURN VALUE
+On success,
+.BR getpriority ()
+returns the calling thread's nice value, which may be a negative number.
+On error, it returns \-1 and sets
+.I errno
+to indicate the cause of the error.
+Since a successful call to
+.BR getpriority ()

 can legitimately return the value \-1, it is necessary
 to clear the external variable
 .I errno
 prior to the
 can legitimately return the value \-1, it is necessary
 to clear the external variable
 .I errno
 prior to the

-call, then check it afterwards to determine
-if a \-1 is an error or a legitimate value.
-The
-.B setpriority
-call returns 0 if there is no error, or
-\-1 if there is.
+call, then check it afterward to determine
+if \-1 is an error or a legitimate value.
+
+.BR setpriority ()
+returns 0 on success.
+On error, it returns \-1 and sets
+.I errno
+to indicate the cause of the error.

 .SH ERRORS
 .TP
 .B EINVAL
 .SH ERRORS
 .TP
 .B EINVAL


@@ -121,42 +149,64 @@ or
 .BR PRIO_USER .
 .TP
 .B ESRCH
 .BR PRIO_USER .
 .TP
 .B ESRCH

-No process was located using the 
+No process was located using the

 .I which
 and
 .I who
 values specified.
 .PP
 In addition to the errors indicated above,
 .I which
 and
 .I who
 values specified.
 .PP
 In addition to the errors indicated above,

-.B setpriority
+.BR setpriority ()

 may fail if:
 .TP
 may fail if:
 .TP

+.B EACCES
+The caller attempted to set a lower nice value
+(i.e., a higher process priority), but did not
+have the required privilege (on Linux: did not have the
+.B CAP_SYS_NICE
+capability).
+.TP

 .B EPERM
 A process was located, but its effective user ID did not match
 either the effective or the real user ID of the caller,
 .B EPERM
 A process was located, but its effective user ID did not match
 either the effective or the real user ID of the caller,

-and (on Linux systems) the caller did not have the 
+and was not privileged (on Linux: did not have the

 .B CAP_SYS_NICE
 .B CAP_SYS_NICE

-capability.
-.TP
-.B EACCES
-A non superuser attempted to lower a process priority.
+capability).
+But see NOTES below.
+.SH CONFORMING TO
+POSIX.1-2001, POSIX.1-2008,
+SVr4, 4.4BSD (these interfaces first appeared in 4.2BSD).

 .SH NOTES
 .SH NOTES

-The details on the condition for EPERM depend on the system.
-The above description is what SUSv3 says, and seems to be followed on
-all SYSV-like systems.
-Linux requires the real or effective user ID of the caller to match
+For further details on the nice value, see
+.BR sched (7).
+
+.IR Note :
+the addition of the "autogroup" feature in Linux 2.6.38 means that
+the nice value no longer has its traditional effect in many circumstances.
+For details, see
+.BR sched (7).
+
+A child created by
+.BR fork (2)
+inherits its parent's nice value.
+The nice value is preserved across
+.BR execve (2).
+
+The details on the condition for
+.B EPERM
+depend on the system.
+The above description is what POSIX.1-2001 says, and seems to be followed on
+all System\ V-like systems.
+Linux kernels before 2.6.12 required the real or
+effective user ID of the caller to match

 the real user of the process \fIwho\fP (instead of its effective user ID).
 the real user of the process \fIwho\fP (instead of its effective user ID).

-All BSD-like systems (SunOS 4.1.3, Ultrix 4.2,
-BSD 4.3, FreeBSD 4.3, OpenBSD-2.5, ...) require
+Linux 2.6.12 and later require

 the effective user ID of the caller to match
 the real or effective user ID of the process \fIwho\fP.
 the effective user ID of the caller to match
 the real or effective user ID of the process \fIwho\fP.

-.LP
-The actual priority range varies between kernel versions.
-Linux before 1.3.36 had -infinity..15. Linux since 1.3.43 has -20..19,
-and the system call getpriority returns 40..1 for these values
-(since negative numbers are error codes).
-The library call converts N into 20-N.
-.LP
+All BSD-like systems (SunOS 4.1.3, Ultrix 4.2,
+4.3BSD, FreeBSD 4.3, OpenBSD-2.5, ...) behave in the same
+manner as Linux 2.6.12 and later.
+

 Including
 .I <sys/time.h>
 is not required these days, but increases portability.
 Including
 .I <sys/time.h>
 is not required these days, but increases portability.


@@ -168,10 +218,35 @@ structure with fields of type
 .I struct timeval
 defined in
 .IR <sys/time.h> .)
 .I struct timeval
 defined in
 .IR <sys/time.h> .)

-.SH "CONFORMING TO"
-SVr4, 4.4BSD (these function calls first appeared in 4.2BSD).
-.SH "SEE ALSO"
+.\"
+.SS C library/kernel differences
+Within the kernel, nice values are actually represented
+using the range 40..1
+(since negative numbers are error codes) and these are the values
+employed by the
+.BR setpriority ()
+and
+.BR 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
+.IR "unice\ =\ 20\ \-\ knice" .
+(Thus, the kernel's 40..1 range corresponds to the
+range \-20..19 as seen by user space.)
+.SH BUGS
+According 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.
+.SH SEE ALSO

 .BR nice (1),
 .BR nice (1),

+.BR renice (1),

 .BR fork (2),
 .BR capabilities (7),
 .BR fork (2),
 .BR capabilities (7),

-.BR renice (8)
+.BR sched (7)
+
+.I Documentation/scheduler/sched-nice-design.txt
+in the Linux kernel source tree (since Linux 2.6.23)