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diff --git a/sag-0.6.1-www/sag-0.6.1.html/x1495.html b/sag-0.6.1-www/sag-0.6.1.html/x1495.html new file mode 100644 index 0000000..ef14a84 --- /dev/null +++ b/sag-0.6.1-www/sag-0.6.1.html/x1495.html @@ -0,0 +1,287 @@ +<!DOCTYPE HTML PUBLIC "-//Norman Walsh//DTD DocBook HTML 1.0//EN"> +<HTML +><HEAD +><TITLE +>Using a swap space</TITLE +><META +NAME="GENERATOR" +CONTENT="Modular DocBook HTML Stylesheet"><LINK +REL="HOME" +TITLE="The Linux System Administrators' Guide" +HREF="book1.html"><LINK +REL="UP" +TITLE="Memory Management" +HREF="c1450.html"><LINK +REL="PREVIOUS" +TITLE="Creating a swap space" +HREF="x1466.html"><LINK +REL="NEXT" +TITLE="Sharing swap spaces with other operating systems" +HREF="x1529.html"></HEAD +><BODY +BGCOLOR="#FFFFFF" +TEXT="#000000" +><DIV +CLASS="NAVHEADER" +><TABLE +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TH +COLSPAN="3" +ALIGN="center" +>The Linux System Administrators' Guide</TH +></TR +><TR +><TD +WIDTH="10%" +ALIGN="left" +VALIGN="bottom" +><A +HREF="x1466.html" +>Prev</A +></TD +><TD +WIDTH="80%" +ALIGN="center" +VALIGN="bottom" +>Chapter 5. Memory Management</TD +><TD +WIDTH="10%" +ALIGN="right" +VALIGN="bottom" +><A +HREF="x1529.html" +>Next</A +></TD +></TR +></TABLE +><HR +ALIGN="LEFT" +WIDTH="100%"></DIV +><DIV +CLASS="SECT1" +><H1 +CLASS="SECT1" +><A +NAME="AEN1495" +>Using a swap space</A +></H1 +><P +>An initialized swap space is taken into use with + <B +CLASS="COMMAND" +>swapon</B +>. This command tells the kernel that + the swap space can be used. The path to the swap space is given + as the argument, so to start swapping on a temporary swap file + one might use the following command. + +<PRE +CLASS="SCREEN" +><TT +CLASS="PROMPT" +>$</TT +> <TT +CLASS="USERINPUT" +><B +>swapon /extra-swap</B +></TT +> +<TT +CLASS="PROMPT" +>$</TT +></PRE +> + + Swap spaces can be used automatically by listing them in + the <TT +CLASS="FILENAME" +>/etc/fstab</TT +> file. + +<PRE +CLASS="SCREEN" +>/dev/hda8 none swap sw 0 0 +/swapfile none swap sw 0 0</PRE +> + + The startup scripts will run the command <B +CLASS="COMMAND" +>swapon + -a</B +>, which will start swapping on all the swap + spaces listed in <B +CLASS="COMMAND" +>/etc/fstab</B +>. Therefore, + the <B +CLASS="COMMAND" +>swapon</B +> command is usually used only when + extra swap is needed.</P +><P +>You can monitor the use of swap spaces with + <B +CLASS="COMMAND" +>free</B +>. It will tell the total amount of swap + space used. + +<PRE +CLASS="SCREEN" +><TT +CLASS="PROMPT" +>$</TT +> <TT +CLASS="USERINPUT" +><B +>free</B +></TT +> +<TT +CLASS="COMPUTEROUTPUT" +> total used free shared buffers +Mem: 15152 14896 256 12404 2528 +-/+ buffers: 12368 2784 +Swap: 32452 6684 25768</TT +> +<TT +CLASS="PROMPT" +>$</TT +></PRE +> + + The first line of output (<TT +CLASS="LITERAL" +>Mem:</TT +>) shows the + physical memory. The total column does not show the physical + memory used by the kernel, which is usually about a megabyte. + The used column shows the amount of memory used (the second + line does not count buffers). The free column shows completely + unused memory. The shared column shows the amount of memory + shared by several processes; the more, the merrier. The buffers + column shows the current size of the disk buffer cache.</P +><P +>That last line (<TT +CLASS="LITERAL" +>Swap:</TT +>) shows similar + information for the swap spaces. If this line is all zeroes, + your swap space is not activated.</P +><P +>The same information is available via + <B +CLASS="COMMAND" +>top</B +>, or using the proc filesystem in file + <TT +CLASS="FILENAME" +>/proc/meminfo</TT +>. It is currently difficult + to get information on the use of a specific swap space.</P +><P +>A swap space can be removed from use with + <B +CLASS="COMMAND" +>swapoff</B +>. It is usually not necessary to do it, + except for temporary swap spaces. Any pages in use in the swap + space are swapped in first; if there is not sufficient physical + memory to hold them, they will then be swapped out (to some other + swap space). If there is not enough virtual memory to hold all + of the pages Linux will start to thrash; after a long while it + should recover, but meanwhile the system is unusable. You should + check (e.g., with <B +CLASS="COMMAND" +>free</B +>) that there is enough + free memory before removing a swap space from use.</P +><P +>All the swap spaces that are used automatically + with <B +CLASS="COMMAND" +>swapon -a</B +> can be removed from use + with <B +CLASS="COMMAND" +>swapoff -a</B +>; it looks at the file + <TT +CLASS="FILENAME" +>/etc/fstab</TT +> to find what to remove. + Any manually used swap spaces will remain in use.</P +><P +>Sometimes a lot of swap space can be in use even though + there is a lot of free physical memory. This can happen for + instance if at one point there is need to swap, but later a big + process that occupied much of the physical memory terminates + and frees the memory. The swapped-out data is not automatically + swapped in until it is needed, so the physical memory may remain + free for a long time. There is no need to worry about this, + but it can be comforting to know what is happening. </P +></DIV +><DIV +CLASS="NAVFOOTER" +><HR +ALIGN="LEFT" +WIDTH="100%"><TABLE +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +><A +HREF="x1466.html" +>Prev</A +></TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +><A +HREF="book1.html" +>Home</A +></TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +><A +HREF="x1529.html" +>Next</A +></TD +></TR +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +>Creating a swap space</TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +><A +HREF="c1450.html" +>Up</A +></TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +>Sharing swap spaces with other operating systems</TD +></TR +></TABLE +></DIV +></BODY +></HTML +>
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