schedutils/ionice.1

   1 .TH IONICE 1 "July 2011" "util-linux" "User Commands"
   2 .SH NAME
   3 ionice \- set or get process I/O scheduling class and priority
   4 .SH SYNOPSIS
   5 .B ionice
   6 .RB [ \-c
   7 .IR class ]
   8 .RB [ \-n
   9 .IR level ]
  10 .RB [ \-t ]
  11 .B \-p
  12 .IR PID ...
  13 .br
  14 .B ionice
  15 .RB [ \-c
  16 .IR class ]
  17 .RB [ \-n
  18 .IR level ]
  19 .RB [ \-t ]
  20 .B \-P
  21 .IR PGID ...
  22 .br
  23 .B ionice
  24 .RB [ \-c
  25 .IR class ]
  26 .RB [ \-n
  27 .IR level ]
  28 .RB [ \-t ]
  29 .B \-u
  30 .IR UID ...
  31 .br
  32 .B ionice
  33 .RB [ \-c
  34 .IR class ]
  35 .RB [ \-n
  36 .IR level ]
  37 .RB [ \-t ]
  38 .IR "command " [ argument ...]
  39 .SH DESCRIPTION
  40 This program sets or gets the I/O scheduling class and priority for a program.
  41 If no arguments or just \fB\-p\fR is given, \fBionice\fR will query the current
  42 I/O scheduling class and priority for that process.
  43
  44 When \fIcommand\fR is given,
  45 .B ionice
  46 will run this command with the given arguments.
  47 If no \fIclass\fR is specified, then
  48 .I command
  49 will be executed with the "best-effort" scheduling class.  The default
  50 priority level is 4.
  51
  52 As of this writing, a process can be in one of three scheduling classes:
  53 .IP "\fBIdle\fP"
  54 A program running with idle I/O priority will only get disk time when no other
  55 program has asked for disk I/O for a defined grace period.  The impact of an
  56 idle I/O process on normal system activity should be zero.  This scheduling
  57 class does not take a priority argument.  Presently, this scheduling class
  58 is permitted for an ordinary user (since kernel 2.6.25).
  59 .IP "\fBBest-effort\fP"
  60 This is the effective scheduling class for any process that has not asked for
  61 a specific I/O priority.
  62 This class takes a priority argument from \fI0-7\fR, with a lower
  63 number being higher priority.  Programs running at the same best-effort
  64 priority are served in a round-robin fashion.
  65
  66 Note that before kernel 2.6.26 a process that has not asked for an I/O priority
  67 formally uses "\fBnone\fP" as scheduling class, but the I/O scheduler will treat
  68 such processes as if it were in the best-effort class.  The priority within the
  69 best-effort class will be dynamically derived from the CPU nice level of the
  70 process: io_priority = (cpu_nice + 20) / 5.
  71
  72 For kernels after 2.6.26 with the CFQ I/O scheduler, a process that has not asked
  73 for an I/O priority inherits its CPU scheduling class.  The I/O priority is derived
  74 from the CPU nice level of the process (same as before kernel 2.6.26).
  75
  76 .IP "\fBRealtime\fP"
  77 The RT scheduling class is given first access to the disk, regardless of
  78 what else is going on in the system.  Thus the RT class needs to be used with
  79 some care, as it can starve other processes.  As with the best-effort class,
  80 8 priority levels are defined denoting how big a time slice a given process
  81 will receive on each scheduling window.  This scheduling class is not
  82 permitted for an ordinary (i.e., non-root) user.
  83 .SH OPTIONS
  84 .TP
  85 .BR \-c , " \-\-class " \fIclass\fR
  86 Specify the name or number of the scheduling class to use; \fI0\fR for none,
  87 \fI1\fR for realtime, \fI2\fR for best-effort, \fI3\fR for idle.
  88 .TP
  89 .BR \-n , " \-\-classdata " \fIlevel\fR
  90 Specify the scheduling class data.  This only has an effect if the class
  91 accepts an argument.  For realtime and best-effort, \fI0-7\fR are valid data
  92 (priority levels), and \fI0\fR represents the highest priority level.
  93 .TP
  94 .BR \-p , " \-\-pid " \fIPID\fR...
  95 Specify the process IDs of running processes for which to get or set the
  96 scheduling parameters.
  97 .TP
  98 .BR \-P , " \-\-pgid " \fIPGID\fR...
  99 Specify the process group IDs of running processes for which to get or set the
 100 scheduling parameters.
 101 .TP
 102 .BR \-t , " \-\-ignore"
 103 Ignore failure to set the requested priority.  If \fIcommand\fR was specified,
 104 run it even in case it was not possible to set the desired scheduling priority,
 105 which can happen due to insufficient privileges or an old kernel version.
 106 .TP
 107 .BR \-h , " \-\-help"
 108 Display help text and exit.
 109 .TP
 110 .BR \-u , " \-\-uid " \fIUID\fR...
 111 Specify the user IDs of running processes for which to get or set the
 112 scheduling parameters.
 113 .TP
 114 .BR \-V , " \-\-version"
 115 Display version information and exit.
 116 .SH EXAMPLES
 117 .LP
 118 .TP 7
 119 # \fBionice\fP -c 3 -p 89
 120 .TP 7
 121 Sets process with PID 89 as an idle I/O process.
 122 .TP 7
 123 # \fBionice\fP -c 2 -n 0 bash
 124 .TP 7
 125 Runs 'bash' as a best-effort program with highest priority.
 126 .TP 7
 127 # \fBionice\fP -p 89 91
 128 .TP 7
 129 Prints the class and priority of the processes with PID 89 and 91.
 130 .SH NOTES
 131 Linux supports I/O scheduling priorities and classes since 2.6.13 with the CFQ
 132 I/O scheduler.
 133 .SH AUTHORS
 134 .nf
 135 Jens Axboe <jens@axboe.dk>
 136 Karel Zak <kzak@redhat.com>
 137 .fi
 138 .SH SEE ALSO
 139 .BR ioprio_set (2)
 140 .SH AVAILABILITY
 141 The ionice command is part of the util-linux package and is available from
 142 https://www.kernel.org/pub/linux/utils/util-linux/.