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<TITLE>Administration Reference</TITLE>
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<META HTTP-EQUIV="updated" CONTENT="Tue, 03 Oct 2000 16:18:29">
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<H1>Administration Reference</H1>
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<HR><P ALIGN="center"> <A HREF="../index.htm"><IMG SRC="../books.gif" BORDER="0" ALT="[Return to Library]"></A> <A HREF="auarf002.htm#ToC"><IMG SRC="../toc.gif" BORDER="0" ALT="[Contents]"></A> <A HREF="auarf163.htm"><IMG SRC="../prev.gif" BORDER="0" ALT="[Previous Topic]"></A> <A HREF="#Bot_Of_Page"><IMG SRC="../bot.gif" BORDER="0" ALT="[Bottom of Topic]"></A> <A HREF="auarf165.htm"><IMG SRC="../next.gif" BORDER="0" ALT="[Next Topic]"></A> <A HREF="auarf284.htm#HDRINDEX"><IMG SRC="../index.gif" BORDER="0" ALT="[Index]"></A> <P>
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<P>
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<H2><A NAME="HDRFS_STOREBEHIND" HREF="auarf002.htm#ToC_178">fs storebehind</A></H2>
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<A NAME="IDX4985"></A>
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<A NAME="IDX4986"></A>
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<P><STRONG>Purpose</STRONG>
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<P>Enables asynchronous writes to the file server
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<P><STRONG>Synopsis</STRONG>
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<PRE><B>fs storebehind</B> [<B>-kbytes</B> <<VAR>asynchrony for specified names</VAR>>]
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[<B>-files</B> <<VAR>specific pathnames</VAR>><SUP>+</SUP>]
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[<B>-allfiles</B> <<VAR>new default (KB)</VAR>>] [<B>-verbose</B>] [<B>-help</B>]
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<B>fs st</B> [<B>-k</B> <<VAR>asynchrony for specified names</VAR>>] [<B>-f</B> <<VAR>specific pathnames</VAR>><SUP>+</SUP>]
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[<B>-a</B> <<VAR>new default (KB)</VAR>>] [<B>-v</B>] [<B>-h</B>]
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</PRE>
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<P><STRONG>Description</STRONG>
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<P>The <B>fs storebehind</B> command enables the Cache Manager to perform
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a delayed asynchronous write to the File Server when an application closes a
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file. By default, the Cache Manager writes all data to the File Server
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immediately and synchronously when an application program closes a
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file--that is, the <B>close</B> system call does not return until the
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Cache Manager has actually transferred the final chunk of the file to the File
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Server. This command specifies the number of kilobytes of a file that
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can still remain to be written to the File Server when the Cache Manager
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returns control to the application. It is useful if users working on
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the machine commonly work with very large files, but also introduces the
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complications discussed in the <B>Cautions</B> section.
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<P>Set either or both of the following in a single command:
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<UL>
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<P><LI>To set a value that applies to all AFS files manipulated by applications
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running on the machine, use the <B>-allfiles</B> argument. This
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value is termed the <I>default store asynchrony</I> for the machine, and
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persists until the machine reboots. If it is not set, the default value
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is zero, indicating that the Cache Manager performs synchronous writes.
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<P>
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<P>As an example, the following setting means that when an application closes
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a file, the Cache Manager can return control to the application as soon as no
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more than 10 kilobytes of the file remain to be written to the File
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Server.
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<PRE> <B>-allfiles 10</B>
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</PRE>
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<P><LI>To set a value that applies to one or more individual files, and overrides
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the value of the <B>-allfiles</B> argument for them, combine the
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<B>-kbytes</B> and <B>-files</B> arguments. The setting
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persists as long as there is an entry for the file in the kernel table that
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the Cache Manager uses to track certain information about files. In
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general, such an entry persists at least until an application closes the file
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or exits, but the Cache Manager is free to recycle the entry if the file is
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inactive and it needs to free up slots in the table. To increase the
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certainty that there is an entry for the file in the table, issue the <B>fs
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storebehind</B> command shortly before closing the file.
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<P>As an example, the following setting means that when an application closes
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either of the files <B>bigfile</B> and <B>biggerfile</B>, the Cache
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Manager can return control to the application as soon as no more than a
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megabyte of the file remains to be written to the File Server.
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<PRE> <B>-kbytes 1024 -files bigfile biggerfile</B>
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</PRE>
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<P>Note that once an explicit value has been set for a file, the only way to
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make it subject to the default store asynchrony once again is to set
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<B>-kbytes</B> to that value. In other words, there is no
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combination of arguments that automatically makes a file subject to the
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default store asynchrony once another value has been set for the file.
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</UL>
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<P>To display the settings that currently apply to individual files or to all
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files, provide the command's arguments in certain combinations as
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specified in the <B>Output</B> section of this reference page.
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<P><STRONG>Cautions</STRONG>
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<P>For the following reasons, use of this command is not recommended in most
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cases.
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<P>In normal circumstances, an asynchronous setting results in the Cache
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Manager returning control to applications earlier than it otherwise does, but
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this is not guaranteed.
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<P>If a delayed write fails, there is no way to notify the application, since
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the <B>close</B> system call has already returned with a code indicating
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success.
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<P>Writing asynchronously increases the possibility that the user will not
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notice if a write operation makes the volume that houses the file exceed its
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quota. As always, the portion of the file that exceeds the
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volume's quota is lost, which prompts a message such as the
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following:
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<PRE> No space left on device
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</PRE>
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<P>To avoid losing data, it is advisable to verify that the volume housing the
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file has space available for the amount of data anticipated to be
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written.
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<P><STRONG>Options</STRONG>
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<DL>
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<P><DT><B>-kbytes
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</B><DD>Specifies the number of kilobytes of data from each file named by the
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<B>-files</B> argument that can remain to be written to the file server
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when the Cache Manager returns control to an application program that closed
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the file. The <B>-files</B> argument is required along with this
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argument. Provide an integer from the range <B>0</B> (which
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reinstates the Cache Manager's default behavior or writing synchronously)
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to the maximum AFS file size.
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<P><DT><B>-files
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</B><DD>Names each file to which the value set with the <B>-kbytes</B>
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argument applies. The setting persists as long as there is an entry for
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the file in the kernel table that the Cache Manager uses to track certain
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information about files. Because closing a file generally erases the
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entry, when reopening a file the only way to guarantee that the setting still
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applies is to reissue the command. If this argument is provided without
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the <B>-kbytes</B> argument, the command reports the current setting for
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the specified files, and the default store asynchrony.
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<P><DT><B>-allfiles
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</B><DD>Sets the default store asynchrony for the local machine, which is the
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number of kilobytes of data that can remain to be written to the file server
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when the Cache Manager returns control to the application program that closed
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a file. The value applies to all AFS files manipulated by applications
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running on the machine, except those for which settings have been made with
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the <B>-kbytes</B> and <B>-files</B> arguments. Provide an
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integer from the range <B>0</B> (which indicates the default of
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synchronous writes) to the maximum AFS file size.
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<P><DT><B>-verbose
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</B><DD>Produces output confirming the settings made with the accompanying
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<B>-kbytes</B> and <B>-files</B> arguments, the <B>-allfiles</B>
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argument, or all three. If provided by itself, reports the current
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default store asynchrony.
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<P><DT><B>-help
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</B><DD>Prints the online help for this command. All other valid options
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are ignored.
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</DL>
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<P><STRONG>Output</STRONG>
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<P>If none of the command's options are included, or if only the
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<B>-verbose</B> flag is included, the following message reports the
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default store asynchrony (the setting that applies to all files manipulated by
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applications running on the local machine and for which not more specific
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asynchrony is set).
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<PRE> Default store asynchrony is <VAR>x</VAR> kbytes.
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</PRE>
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<P>A value of <TT>0</TT> (zero) indicates synchronous writes and is the
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default if no one has included the <B>-allfiles</B> argument on this
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command since the machine last rebooted.
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<P>If the <B>-files</B> argument is provided without the
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<B>-kbytes</B> argument, the output reports the value that applies to each
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specified file along with the default store asynchrony. If a particular
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value has previously been set for a file, the following message reports
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it:
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<PRE> Will store up to <VAR>y</VAR> kbytes of <VAR>file</VAR> asynchronously.
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Default store asynchrony is <VAR>x</VAR> kbytes.
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</PRE>
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<P>If the default store asynchrony applies to a file because no explicit
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<B>-kbytes</B> value has been set for it, the message is instead as
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follows:
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<PRE> Will store <VAR>file</VAR> according to default.
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Default store asynchrony is <VAR>x</VAR> kbytes.
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</PRE>
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<P>If the <B>-verbose</B> flag is combined with arguments that set values
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(<B>-files</B> and <B>-kbytes</B>, or <B>-allfiles</B>, or all
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three), there is a message that confirms immediately that the setting has
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taken effect. When included without other arguments or flags, the
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<B>-verbose</B> flag reports the default store asynchrony only.
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<P><STRONG>Examples</STRONG>
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<P>The following command enables the Cache Manager to return control to the
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application program that closed the file <B>test.data</B> when 100
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kilobytes still remain to be written to the File Server. The
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<B>-verbose</B> flag produces output that confirms the new setting, and
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that the default store asynchrony is zero.
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<PRE> % <B>fs storebehind -kbytes 100 -files test.data -verbose</B>
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Will store up to 100 kbytes of test.data asynchronously.
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Default store asynchrony is 0 kbytes.
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</PRE>
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<P><STRONG>Privilege Required</STRONG>
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<P>To include the <B>-allfiles</B> argument, the issuer must be logged in
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as the local superuser <B>root</B>.
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<P>To include the <B>-kbytes</B> and <B>-files</B> arguments, the
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issuer must either be logged in as the local superuser <B>root</B> or have
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the <B>w</B> (<B>write</B>) permission on the ACL of each file's
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directory.
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<P>To view the current settings (by including no arguments, the
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<B>-file</B> argument alone, or the <B>-verbose</B> argument alone),
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no privilege is required.
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<P><STRONG>Related Information</STRONG>
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<P><A HREF="auarf058.htm#HDRAFSD">afsd</A>
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<P>
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<HR><P ALIGN="center"> <A HREF="../index.htm"><IMG SRC="../books.gif" BORDER="0" ALT="[Return to Library]"></A> <A HREF="auarf002.htm#ToC"><IMG SRC="../toc.gif" BORDER="0" ALT="[Contents]"></A> <A HREF="auarf163.htm"><IMG SRC="../prev.gif" BORDER="0" ALT="[Previous Topic]"></A> <A HREF="#Top_Of_Page"><IMG SRC="../top.gif" BORDER="0" ALT="[Top of Topic]"></A> <A HREF="auarf165.htm"><IMG SRC="../next.gif" BORDER="0" ALT="[Next Topic]"></A> <A HREF="auarf284.htm#HDRINDEX"><IMG SRC="../index.gif" BORDER="0" ALT="[Index]"></A> <P>
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