Blog Posts

Linux Server Hacks

I stopped at Borders in downtown Burlington on New Year's Eve day, and found a book called Linux Server Hacks. I loved it immediately, but I wasn't quite willing to shell out $25 for such a slim volume, even if it did have many tidbits I could immediately use.

When I told my co-worker, Rob, about it, it turned out he already had the book, and brought it in to work for me to borrow the next day.

My nose has barely been out of it since. I've done such things as:

  • Create personal firewalls for my home and office machines. I've always used scripts for this, but the hacks for iptables showed the basics of how they work, and I've now got nice robust firewalls that are very simple scripts. To make them even more user-friendly, I borrowed some syntax from the various /etc/init.d scripts so that I can start, stop, and reload the firewall at will.
  • I don't use perl at the command line much, even though I've long known the -e switch; it just seems to cumbersome. However, combine it with the -p and/or -i switch, and you can use perl as a filter on globbed files!
  • I know much more about SSH now, and am using ssh-agent effectively at work now to bounce around servers and transfer groups of files between servers (often by piping tar commands with ssh).
  • A script called movein.sh turned my life around when it came to working on the servers. I now have a .skel directory on my work machine that contains links to oft-used configuration files and directories, as well as to my ~/bin directory; this allows me to then type movein.sh server and have all these files uploaded to the server. I can now use vim, screen, and other programs on any system we have in exactly the manner I expect to.
  • I've started thinking about versioning more, and have plans to put into place a subversion repository to store server configs, database schema, and development projects so we won't make as many mistakes in the future — at least not ones we can't rollback from.
  • I rewrote a shell script in perl that was originally intended for IP takeover, and have been utilizing it to determine if and/or when a server we've reinstalled goes down.
  • A bunch of Apache and MySQL tips are included, including mod_rewrite hacks, how to make your directory indexes show full file names, and more; as well as how to monitor your mysql processes and, if necessary, kill them. I'm also very interested in how to use MySQL as an authentication backend for an FTP daemon — it could give us very fine-grained control of our webserver for editors.

And that's just the tip of the iceberg. All in all, I highly recommend the book — though most likely as a book to check out from the library for a few weeks, digest, put into practice, and return. The hacks are so damn useful, I've found that after using one, I don't need to refer to that one ever again. But that's the point.

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Perl Cookbook, 2nd Edition

Tonight was Papa night, which meant that I got to look after Maeve while Jen worked late doing a group at work. Last week, Maeve and I established that Papa Night would always include going to the bookstore, which means Barnes & Noble in South Burlington.

Last week, Maeve was perfectly content to look at books by herself, and didn't want me interfering, so I decided this week to grab a book for myself to peruse while she was busy. It didn't work as I intended — Maeve saw that I wasn't paying full attention to her, and then demanded my attention — but I was able to look through some of the new items in the second edition of The Perl Cookbook.

Among them were:

  • Setting up both an XML-RPC server and client, using SOAP::Lite

  • Setting up both a SOAP-RPC server and client, using SOAP::Lite and other modules; I could have used this in ROX::Filer to communicate with ROX instead of using the filer's RPC call.

  • Better coverage of DBI (it actually covered it!):

    • When you expect only a single row, this is a nice way to grab it:

      $row = $dbi->selectrow_(array|hash)ref($statement)

    • This is a great way to grab a bunch of columns from a large resultset:

      $results = $dbi->selectall_hashref($sql);
foreach $record (keys(%{$results})) {
    print $results->{$record}{fieldname};
}

    • This one is nice for a large resultset from which you only want one column:

      $results = $dbi->selectcol_arrayref($sql);
foreach $result (@{$results}) {
    print $result;
}

    • If you need to quote values before inserting them, try:

      $quoted = $dbi->quote($unquoted);
$sql = "UPDATE table SET textfield = $quoted";

    • If you need to check for errors, don't check with each DBI call; instead, wrap all of them in an eval statement:

      eval {
    $sth = $dbi->prepare($sql);
    $sth->do;
    while ($row = $sth->fetchrow_hashref) {
        ...
    }
}
if ($@) {
    print $DBI::errstr; 
}

  • Coverage of templating, including Text::Template (very interesting!)

  • Whole new chapters on mod_perl and XML (including DOM!) which I didn't really even get to peruse.

  • autouse pragma: if you use:

    use autouse Module::Name;

    perl will use the module at runtime instead of compiletime; basically, it only uses it if it actually needs it (i.e., if it encounters code that utilizes functionality from that module). It's a good way to keep down on the bloat — I should use this with librox-perl, and possibly with CGI::App.

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