schedutils/ionice.1

   1 .TH ionice "1" "August 2005" ionice
   2 .SH NAME
   3 ionice \- get/set program io scheduling class and priority
   4 .SH SYNOPSIS
   5 .BI "ionice [[\-c " class "] [\-n " classdata " ] [\-t]] \-p " PID " [" PID " ...]"
   6
   7 .BI "ionice [\-c " class "] [\-n " classdata " ] [\-t] COMMAND [ARG ...]"
   8
   9 .SH DESCRIPTION
  10 This program sets or gets the io scheduling class and priority for a program.
  11 If no arguments or just \fI-p\fR is given, \fIionice\fR will query the current
  12 io scheduling class and priority for that process.
  13
  14 As of this writing, a process can be in one of four scheduling classes:
  15
  16 .IP "\fBIdle\fP"
  17 A program running with idle io priority will only get disk time when no other
  18 program has asked for disk io for a defined grace period. The impact of idle
  19 io processes on normal system activity should be zero. This scheduling
  20 class does not take a priority argument. Presently, this scheduling class
  21 is permitted for an ordinary user (since kernel 2.6.25).
  22
  23 .IP "\fBBest effort\fP"
  24 This is the effective scheduling class for any process that hasn't asked for
  25 a specific io priority.
  26 This class takes a priority argument from \fI0-7\fR, with lower
  27 number being higher priority. Programs running at the same best effort
  28 priority are served in a round-robin fashion.
  29
  30 .IP "\fBReal time\fP"
  31 The RT scheduling class is given first access to the disk, regardless of
  32 what else is going on in the system. Thus the RT class needs to be used with
  33 some care, as it can starve other processes. As with the best effort class,
  34 8 priority levels are defined denoting how big a time slice a given process
  35 will receive on each scheduling window. This scheduling class is not
  36 permitted for an ordinary (i.e., non-root) user.
  37
  38 .IP "\fBNone\fP"
  39 A process that that hasn't asked for a specific io priority will formally be
  40 in this class. The io scheduler will treat a process that is in this class as
  41 if it were in the best effort class. The priority within the best effort
  42 class will be dynamically derived from the cpu nice level of the process:
  43 io_priority = (cpu_nice + 20) / 5
  44
  45
  46 .SH OPTIONS
  47 .IP "\fB-c \fIclass\fP"
  48 The scheduling class. \fI1\fR for real time, \fI2\fR for best-effort, \fI3\fR for idle.
  49 .IP "\fB-n \fIclassdata\fP"
  50 The scheduling class data. This defines the class data, if the class
  51 accepts an argument. For real time and best-effort, \fI0-7\fR is valid
  52 data.
  53 .IP "\fB-p \fIpid\fP"
  54 Pass in process PID(s) to view or change already running processes. If this argument
  55 is not given, \fBionice\fP will run the listed program with the given
  56 parameters.
  57 .IP "\fB-t\fP"
  58 Ignore failure to set requested priority. If COMMAND or PID(s) is specified, run it
  59 even in case it was not possible to set desired scheduling priority, what
  60 can happen due to insufficient privilegies or old kernel version.
  61
  62 .SH EXAMPLES
  63 .LP
  64 .TP 7
  65 # \fBionice\fP -c 3 -p 89
  66 .TP 7
  67 Sets process with PID 89 as an idle io process.
  68 .TP 7
  69 # \fBionice\fP -c 2 -n 0 bash
  70 .TP 7
  71 Runs 'bash' as a best-effort program with highest priority.
  72 .TP 7
  73 # \fBionice\fP -p 89 91
  74 .TP 7
  75 Prints the class and priority of the processes with PID 89 and 91.
  76
  77 .SH NOTES
  78 Linux supports io scheduling priorities and classes since 2.6.13 with the CFQ
  79 io scheduler.
  80
  81 .SH AUTHORS
  82 Jens Axboe <axboe@suse.de>
  83
  84 .SH AVAILABILITY
  85 The ionice command is part of the util-linux-ng package and is available from
  86 ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.