bsd/man/man2/getpriority.2

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  34 .\"     @(#)getpriority.2       8.1 (Berkeley) 6/4/93
  35 .\"
  36 .Dd June 4, 1993
  37 .Dt GETPRIORITY 2
  38 .Os BSD 4
  39 .Sh NAME
  40 .Nm getpriority ,
  41 .Nm setpriority
  42 .Nd get/set program scheduling priority
  43 .Sh SYNOPSIS
  44 .Fd #include <sys/resource.h>
  45 .Ft int
  46 .Fo getpriority
  47 .Fa "int which"
  48 .Fa "id_t who"
  49 .Fc
  50 .Ft int
  51 .Fo setpriority
  52 .Fa "int which"
  53 .Fa "id_t who"
  54 .Fa "int prio"
  55 .Fc
  56 .Sh DESCRIPTION
  57 The scheduling
  58 priority of the process, process group, or user as indicated by
  59 .Fa which
  60 and
  61 .Fa who
  62 is obtained with the
  63 .Fn getpriority
  64 call and set with the
  65 .Fn setpriority
  66 call.  Additionally, the current thread can be set to background
  67 state.
  68 .Fa Which
  69 is one of
  70 .Dv PRIO_PROCESS ,
  71 .Dv PRIO_PGRP ,
  72 .Dv PRIO_USER ,
  73 or
  74 .Dv PRIO_DARWIN_THREAD ,
  75 and
  76 .Fa who
  77 is interpreted relative to
  78 .Fa which
  79 (a process identifier for
  80 .Dv PRIO_PROCESS ,
  81 process group
  82 identifier for
  83 .Dv PRIO_PGRP ,
  84 and a user ID for
  85 .Dv PRIO_USER ) .
  86 A zero value of
  87 .Fa who
  88 denotes the current process, process group, user, thread (for PRIO_DARWIN_THREAD).
  89 .Fa prio
  90 is a value in the range -20 to 20.  The default priority is 0;
  91 lower priorities cause more favorable scheduling.
  92 For PRIO_DARWIN_THREAD,
  93 .Fa prio
  94 is either 0 (to remove current thread from background status) or PRIO_DARWIN_BG
  95 (to set current thread into background state).
  96 .Pp
  97 The
  98 .Fn getpriority
  99 call returns the highest priority (lowest numerical value)
 100 enjoyed by any of the specified processes or for PRIO_DARWIN_THREAD
 101 returns 0 when current thread is not in background state or 1
 102 when the current thread is in background state.
 103 The
 104 .Fn setpriority
 105 call sets the priorities of all of the specified processes
 106 to the specified value.  When setting a thread into background
 107 state the scheduling priority is set to lowest value, disk and
 108 network IO are throttled.  Network IO will be throttled for any
 109 sockets the thread opens after going into background state.  Any
 110 previously opened sockets are not affected.
 111 Only the super-user may lower priorities, but any thread can set
 112 itself into background state.
 113 .Sh RETURN VALUES
 114 Since
 115 .Fn getpriority
 116 can legitimately return the value -1, it is necessary
 117 to clear the external variable
 118 .Va errno
 119 prior to the
 120 call, then check it afterward to determine
 121 if a -1 is an error or a legitimate value.
 122 The
 123 .Fn setpriority
 124 call returns 0 if there is no error, or
 125 -1 if there is.
 126 .Sh ERRORS
 127 .Fn Getpriority
 128 and
 129 .Fn setpriority
 130 will fail if:
 131 .Bl -tag -width Er
 132 .\" ==========
 133 .It Bq Er EINVAL
 134 .Fa Which
 135 is not one of
 136 .Dv PRIO_PROCESS ,
 137 .Dv PRIO_PGRP ,
 138 .Dv PRIO_USER ,
 139 or
 140 .Dv PRIO_DARWIN_THREAD .
 141 .\" ==========
 142 .It Bq Er EINVAL
 143 .Fa Who
 144 is not a valid process, process group, or user ID.
 145 .\" ==========
 146 .It Bq Er EINVAL
 147 .Fa Who
 148 is not 0 when
 149 .Fa which
 150 is PRIO_DARWIN_THREAD.
 151 .\" ==========
 152 .It Bq Er ESRCH
 153 No process can be located using the
 154 .Fa which
 155 and
 156 .Fa who
 157 values specified.
 158 .El
 159 .Pp
 160 .Bl -tag -width Er
 161 In addition to the errors indicated above,
 162 .Fn setpriority
 163 will fail if:
 164 .\" ==========
 165 .It Bq Er EACCES
 166 A non super-user attempts to lower a process priority.
 167 .\" ==========
 168 .It Bq Er EPERM
 169 A process is located,
 170 but neither its effective nor real user ID
 171 matches the effective user ID of the caller.
 172 .El
 173 .Sh LEGACY SYNOPSIS
 174 .Fd #include <sys/types.h>
 175 .Fd #include <sys/resource.h>
 176 .Pp
 177 The include file
 178 .In sys/types.h
 179 is necessary.
 180 .Pp
 181 .Ft int
 182 .br
 183 .Fo getpriority
 184 .Fa "int which"
 185 .Fa "int who"
 186 .Fc ;
 187 .Pp
 188 .Ft int
 189 .br
 190 .Fo setpriority
 191 .Fa "int which"
 192 .Fa "int who"
 193 .Fa "int value"
 194 .Fc ;
 195 .Pp
 196 The type of
 197 .Fa who
 198 has changed.
 199 .Sh SEE ALSO
 200 .Xr nice 1 ,
 201 .Xr fork 2 ,
 202 .Xr compat 5 ,
 203 .Xr renice 8
 204 .Sh HISTORY
 205 The
 206 .Fn getpriority
 207 function call appeared in
 208 .Bx 4.2 .