man2/swapon.2

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   3 .\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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  26 .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
  27 .\" Modified 1995-07-22 by Michael Chastain <mec@duracef.shout.net>
  28 .\" Modified 1995-07-23 by aeb
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  32 .\" Modified 2004-10-10 by aeb
  33 .\" 2004-12-14 mtk, Anand Kumria: added new errors
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  35 .TH SWAPON 2 2004-10-10 "Linux 2.6.7" "Linux Programmer's Manual"
  36 .SH NAME
  37 swapon, swapoff \- start/stop swapping to file/device
  38 .SH SYNOPSIS
  39 .B #include <unistd.h>
  40 .br
  41 .B #include <asm/page.h>     /* to find PAGE_SIZE */
  42 .br
  43 .B #include <sys/swap.h>
  44 .sp
  45 .BI "int swapon(const char *" path ", int " swapflags );
  46 .br
  47 .BI "int swapoff(const char *" path );
  48 .SH DESCRIPTION
  49 .BR swapon ()
  50 sets the swap area to the file or block device specified by
  51 .IR path .
  52 .BR swapoff ()
  53 stops swapping to the file or block device specified by
  54 .IR path .
  55 .PP
  56 .BR swapon ()
  57 takes a
  58 .I swapflags
  59 argument.
  60 If
  61 .I swapflags
  62 has the
  63 .I SWAP_FLAG_PREFER
  64 bit turned on, the new swap area will have a higher priority than default.
  65 The priority is encoded within
  66 .I swapflags
  67 as:
  68 .br
  69 .sp
  70 .I "    (prio << SWAP_FLAG_PRIO_SHIFT) & SWAP_FLAG_PRIO_MASK"
  71 .br
  72 .PP
  73 These functions may only be used by a privileged process (one having the
  74 .B CAP_SYS_ADMIN
  75 capability).
  76 .SH PRIORITY
  77 Each swap area has a priority, either high or low.
  78 The default priority is low.
  79 Within the low-priority areas,
  80 newer areas are even lower priority than older areas.
  81 .PP
  82 All priorities set with
  83 .I swapflags
  84 are high-priority, higher than default.
  85 They may have any non-negative value chosen by the caller.
  86 Higher numbers mean higher priority.
  87 .PP
  88 Swap pages are allocated from areas in priority order,
  89 highest priority first.
  90 For areas with different priorities,
  91 a higher-priority area is exhausted before using a lower-priority area.
  92 If two or more areas have the same priority,
  93 and it is the highest priority available,
  94 pages are allocated on a round-robin basis between them.
  95 .PP
  96 As of Linux 1.3.6, the kernel usually follows these rules,
  97 but there are exceptions.
  98 .SH "RETURN VALUE"
  99 On success, zero is returned.
 100 On error, \-1 is returned, and
 101 .I errno
 102 is set appropriately.
 103 .SH ERRORS
 104 .TP
 105 .B EBUSY
 106 (for
 107 .BR swapon ())
 108 The specified
 109 .I path
 110 is already being used as a swap area.
 111 .TP
 112 .B EINVAL
 113 The file
 114 .I path
 115 exists, but refers neither to a regular file nor to a block device;
 116 or, for
 117 .BR swapon (),
 118 the indicated path does not contain a valid swap signature;
 119 or, for
 120 .BR swapoff (),
 121 .I path
 122 is not currently a swap area.
 123 .TP
 124 .B ENFILE
 125 The system limit on the total number of open files has been reached.
 126 .TP
 127 .B ENOENT
 128 The file
 129 .I path
 130 does not exist.
 131 .TP
 132 .B ENOMEM
 133 The system has insufficient memory to start swapping.
 134 .TP
 135 .B EPERM
 136 The caller does not have the
 137 .B CAP_SYS_ADMIN
 138 capability, or all
 139 .B MAX_SWAPFILES
 140 (earlier 8; 32 since Linux 2.4.10) are in use.
 141 .SH "CONFORMING TO"
 142 These functions are Linux specific and should not be used in programs
 143 intended to be portable.
 144 The second
 145 .I swapflags
 146 argument was introduced in Linux 1.3.2.
 147 .SH NOTES
 148 The partition or path must be prepared with
 149 .BR mkswap (8).
 150 .SH "SEE ALSO"
 151 .BR mkswap (8),
 152 .BR swapoff (8),
 153 .BR swapon (8)