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Document why 'cp -i </dev/null' is suggested for archive command.

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This commit is contained in:
Bruce Momjian 2010-03-31 23:35:19 +00:00
parent f185fc3c5e
commit cba3498596
1 changed files with 7 additions and 6 deletions
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13
doc/src/sgml/backup.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.144 2010/02/22 17:15:10 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.145 2010/03/31 23:35:19 momjian Exp $ -->
<chapter id="backup">
<title>Backup and Restore</title>
@ -604,11 +604,12 @@ cp -i pg_xlog/00000001000000A900000065 /mnt/server/archivedir/00000001000000A900
directory).
It is advisable to test your proposed archive command to ensure that it
indeed does not overwrite an existing file, <emphasis>and that it returns
nonzero status in this case</>. We have found that <literal>cp -i</> does
this correctly on some platforms but not others. If the chosen command
does not itself handle this case correctly, you should add a command
to test for existence of the archive file. For example, something
like:
nonzero status in this case</>. On many Unix platforms, <command>cp
-i</> causes copy to prompt before overwriting a file, and
<literal>&lt; /dev/null</> causes the prompt (and overwriting) to
fail. If your platform does not support this behavior, you should
add a command to test for the existence of the archive file. For
example, something like:
<programlisting>
archive_command = 'test ! -f .../%f &amp;&amp; cp %p .../%f'
</programlisting>