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diff --git a/man2/swapon.2 b/man2/swapon.2 new file mode 100644 index 0000000..400f609 --- /dev/null +++ b/man2/swapon.2 @@ -0,0 +1,197 @@ +.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992 +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" Modified by Michael Haardt <michael@moria.de> +.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu> +.\" Modified 1995-07-22 by Michael Chastain <mec@duracef.shout.net> +.\" Modified 1995-07-23 by aeb +.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com> +.\" Modified 1998-09-08 by aeb +.\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" Modified 2004-10-10 by aeb +.\" 2004-12-14 mtk, Anand Kumria: added new errors +.\" 2007-06-22 Ivana Varekova <varekova@redhat.com>, mtk +.\" Update text describing limit on number of swap files. +.\" 2021-01-17 Alex Baranowski <alex@euro-linux.com> +.\" Update information about available swap files decreased by +.\" CONFIG_DEVICE_PRIVATE option. +.\" +.\" FIXME Linux 3.11 added SWAP_FLAG_DISCARD_ONCE and SWAP_FLAG_DISCARD_PAGES +.\" commit dcf6b7ddd7df8965727746f89c59229b23180e5a +.\" Author: Rafael Aquini <aquini@redhat.com> +.\" Date: Wed Jul 3 15:02:46 2013 -0700 +.\" +.TH swapon 2 2023-03-30 "Linux man-pages 6.05.01" +.SH NAME +swapon, swapoff \- start/stop swapping to file/device +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <sys/swap.h> +.PP +.BI "int swapon(const char *" path ", int " swapflags ); +.BI "int swapoff(const char *" path ); +.fi +.SH DESCRIPTION +.BR swapon () +sets the swap area to the file or block device specified by +.IR path . +.BR swapoff () +stops swapping to the file or block device specified by +.IR path . +.PP +If the +.B SWAP_FLAG_PREFER +flag is specified in the +.BR swapon () +.I swapflags +argument, the new swap area will have a higher priority than default. +The priority is encoded within +.I swapflags +as: +.PP +.in +4n +.EX +.I "(prio << SWAP_FLAG_PRIO_SHIFT) & SWAP_FLAG_PRIO_MASK" +.EE +.in +.PP +If the +.B SWAP_FLAG_DISCARD +flag is specified in the +.BR swapon () +.I swapflags +argument, freed swap pages will be discarded before they are reused, +if the swap device supports the discard or trim operation. +(This may improve performance on some Solid State Devices, +but often it does not.) +See also NOTES. +.PP +These functions may be used only by a privileged process (one having the +.B CAP_SYS_ADMIN +capability). +.SS Priority +Each swap area has a priority, either high or low. +The default priority is low. +Within the low-priority areas, +newer areas are even lower priority than older areas. +.PP +All priorities set with +.I swapflags +are high-priority, higher than default. +They may have any nonnegative value chosen by the caller. +Higher numbers mean higher priority. +.PP +Swap pages are allocated from areas in priority order, +highest priority first. +For areas with different priorities, +a higher-priority area is exhausted before using a lower-priority area. +If two or more areas have the same priority, +and it is the highest priority available, +pages are allocated on a round-robin basis between them. +.PP +As of Linux 1.3.6, the kernel usually follows these rules, +but there are exceptions. +.SH RETURN VALUE +On success, zero is returned. +On error, \-1 is returned, and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EBUSY +(for +.BR swapon ()) +The specified +.I path +is already being used as a swap area. +.TP +.B EINVAL +The file +.I path +exists, but refers neither to a regular file nor to a block device; +.TP +.B EINVAL +.RB ( swapon ()) +The indicated path does not contain a valid swap signature or +resides on an in-memory filesystem such as +.BR tmpfs (5). +.TP +.BR EINVAL " (since Linux 3.4)" +.RB ( swapon ()) +An invalid flag value was specified in +.IR swapflags . +.TP +.B EINVAL +.RB ( swapoff ()) +.I path +is not currently a swap area. +.TP +.B ENFILE +The system-wide limit on the total number of open files has been reached. +.TP +.B ENOENT +The file +.I path +does not exist. +.TP +.B ENOMEM +The system has insufficient memory to start swapping. +.TP +.B EPERM +The caller does not have the +.B CAP_SYS_ADMIN +capability. +Alternatively, the maximum number of swap files are already in use; +see NOTES below. +.SH STANDARDS +Linux. +.SH HISTORY +The +.I swapflags +argument was introduced in Linux 1.3.2. +.SH NOTES +The partition or path must be prepared with +.BR mkswap (8). +.PP +There is an upper limit on the number of swap files that may be used, +defined by the kernel constant +.BR MAX_SWAPFILES . +Before Linux 2.4.10, +.B MAX_SWAPFILES +has the value 8; +since Linux 2.4.10, it has the value 32. +Since Linux 2.6.18, the limit is decreased by 2 (thus: 30) +if the kernel is built with the +.B CONFIG_MIGRATION +option +(which reserves two swap table entries for the page migration features of +.BR mbind (2) +and +.BR migrate_pages (2)). +Since Linux 2.6.32, the limit is further decreased by 1 +if the kernel is built with the +.B CONFIG_MEMORY_FAILURE +option. +Since Linux 5.14, the limit is further decreased by 4 +if the kernel is built with the +.B CONFIG_DEVICE_PRIVATE +option. +.PP +Discard of swap pages was introduced in Linux 2.6.29, +then made conditional +on the +.B SWAP_FLAG_DISCARD +flag in Linux 2.6.36, +.\" To be precise: 2.6.35.5 +which still discards the +entire swap area when +.BR swapon () +is called, even if that flag bit is not set. +.SH SEE ALSO +.BR mkswap (8), +.BR swapoff (8), +.BR swapon (8) |