pg_checksystem

#!/usr/bin/perl -wT

# Check various system parameters for PostgreSQL. This needs to be run as root.
#
# (C) 2005-2009 Martin Pitt <mpitt@debian.org>
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.

use strict;

use PgCommon;

# Check write cache setting for given drive.
# Arguments: <device>
# Returns: 0 = disabled, 1 = enabled, -1: could not determine
sub get_device_write_cache {
    open DRV, $_[0] or return -1;
    sub HDIO_GET_WCACHE () {0x30e;}
    my $pval = pack 'l', 0;
    ioctl DRV, &HDIO_GET_WCACHE, $pval or return -1;
    my ($val) = unpack 'l', $pval;
    close DRV;
    return $val;
}


error 'This command needs to be executed as root' if $> != 0;

# collect write cache-enabled drives with databases
my %drive_wcache;
my %seen;
for my $v (get_versions) {
    for my $c (get_version_clusters $v) {
	my $datadir = PgCommon::cluster_data_directory $v, $c;
	my $drv = PgCommon::get_file_device $datadir;
	$drv =~ s/[0-9]+$//;
	unless (exists $seen{$drv}) {
	    $drive_wcache{$drv} = 1 if (get_device_write_cache $drv) > 0;
	    $seen{$drv} = 1;
	}
    }
}
my @unsave_drives = keys %drive_wcache;

if (@unsave_drives) {
    print 'Warning: The following devices contain databases and have write
caching enabled: ', (join ' ', @unsave_drives), '
This could destroy the integrity of your databases in the event of power
failure. Consider disabling the write cache with "hdparm -W 0 <device>".
';
}